. 8
( 19)


specified aging time.
Use aging to remove secure MAC addresses on a secure port without manually deleting the exist-
ing secure MAC addresses. Aging time limits can also be increased to ensure past secure MAC ad-
dresses remain even while new MAC addresses are added. Keep in mind the maximum number of
secure addresses per port can be configured. Aging of statically configured secure addresses can be
enabled or disabled on a per-port basis.
Use the switchport port-security aging {static | time time | type {absolute |
inactivity}} command to enable or disable static aging for the secure port or to set the aging
time or type.
A typical port security configuration for a voice port requires two secure MAC addresses. The ad-
dresses are usually learned dynamically. One MAC address is for the IP phone, and the other ad-
dress is for the PC connected to the IP phone. Violations of this policy result in the port being shut
down. The aging timeout for the learned MAC addresses is set to two hours.

6.3.2 Verifying Port Security
When port security is enabled, the administrator should use show commands to verify that the port
learned the MAC address. Additionally, show commands are useful when monitoring and trou-
bleshooting port-security configurations. They can be used to view information such as the maxi-
mum number of MAC addresses that can be associated with a port, the violation count, and the
current violation mode.
Use the show port-security command to view port security settings for the switch, including vi-
olation count, configured interfaces, and security violation actions.
Use the show port-security [interface interface-id] command to view port security settings
for the specified interface, including the maximum allowed number of secure MAC addresses for
the interface, the number of secure MAC addresses on the interface, the number of security viola-
tions that have occurred, and the violation mode.
Use the show port-security [interface interface-id] address command to view all secure
MAC addresses configured on all switch interfaces or on a specified interface with aging informa-
tion for each address.
Network managers need a way of monitoring who is using the network and where they are. For ex-
ample, if port F2/1 is secure on a switch, an SNMP trap is generated when a MAC address entry
for that port disappears from the MAC address table.
The MAC address notification feature sends SNMP traps to the network management station
(NMS) whenever a new MAC address is added to or an old address is deleted from the forwarding
tables. MAC address notifications are generated only for dynamic and secure MAC addresses.
MAC address notification allows the network administrator to monitor MAC addresses that are
learned as well as MAC addresses that age out and are removed from the switch.
172 CCNA Security Course Booklet, Version 1.0

Use the mac address-table notification global configuration command to enable the MAC
address notification feature on a switch.

6.3.3 Configuring BPDU Guard and Root Guard
To mitigate STP manipulation the PortFast, root guard, and BPDU guard STP enhancement com-
mands can be enabled. These features enforce the placement of the root bridge in the network and
enforce the STP domain borders.
The spanning-tree PortFast feature causes an interface configured as a Layer 2 access port to tran-
sition from the blocking to the forwarding state immediately, bypassing the listening and learning
states. PortFast can be used on Layer 2 access ports that connect to a single workstation or server
to allow those devices to connect to the network immediately, instead of waiting for STP to con-
Because the purpose of PortFast is to minimize the time that access ports must wait for STP to
converge, it should be used only on access ports. If PortFast is enabled on a port connecting to an-
other switch, there is a risk of creating a spanning-tree loop.
This command configures PortFast for all non-trunking ports at once.
Switch(config)# spanning-tree portfast default
This command configures Portfast on an interface.
Switch(config-if)# spanning-tree portfast
This command verifies that PortFast has been configured on an interface.
Switch# show running-config interface FastEthernet 0/8
BPDU Guard
The STP BPDU guard feature allows network designers to keep the active network topology pre-
dictable. BPDU guard is used to protect the switched network from the problems caused by receiv-
ing BPDUs on ports that should not be receiving them. The receipt of unexpected BPDUs might
be accidental or part of an unauthorized attempt to add a switch to the network.
If a port that is configured with PortFast receives a BPDU, STP can put the port into the disabled
state by using BPDU guard.
BPDU guard is best deployed toward user-facing ports to prevent rogue switch network extensions
by an attacking host.
Use this command to enable BPDU guard on all ports with PortFast enabled.
Switch(config)# spanning-tree portfast bpduguard default
To display information about the state of spanning tree, use the show spanning-tree summary
command. In this output, BPDU guard is enabled.
Switch# show spanning-tree summary
Root bridge for: VLAN0001, VLAN0004-VLAN1005
VLAN1013-VLAN1499, VLAN2001-VLAN4094
EtherChannel misconfiguration guard is enabled
Extended system ID is enabled
Portfast is enabled by default
PortFast BPDU Guard is enabled
Portfast BPDU Filter is disabled by default
Loopguard is disabled by default
Chapter 6: Securing the Local Area Network 173

UplinkFast is disabled
BackboneFast is disabled
Pathcost method used is long
<output omitted>
Another useful command to verify BPDU guard configuration is the show spanning-tree sum-
mary totals command.

Root Guard
The Cisco switch root guard feature provides a way to enforce the placement of root bridges in the
network. Root guard limits the switch ports out of which the root bridge can be negotiated. If a
root-guard-enabled port receives BPDUs that are superior to those that the current root bridge is
sending, that port is moved to a root-inconsistent state, which is effectively equal to an STP listen-
ing state, and no data traffic is forwarded across that port.
Because an administrator can manually set the bridge priority of a switch to zero, root guard may
seem unnecessary. Setting the priority of a switch to zero does not guarantee that switch will be
elected as the root bridge, because there might be another switch with a priority of zero and a
lower MAC address, and therefore a lower bridge ID.
Root guard is best deployed toward ports that connect to switches that should not be the root
With root guard, if an attacking host sends out spoofed BPDUs in an effort to become the root
bridge, the switch, upon receipt of a BPDU, ignores the BPDU and puts the port in a root-inconsis-
tent state. The port recovers as soon as the offending BPDUs cease.
BPDU guard and root guard are similar, but their impact is different. BPDU guard disables the
port upon BPDU reception if PortFast is enabled on the port. The disablement effectively denies
devices behind such ports from participating in STP. The administrator must manually re-enable
the port that is put into errdisable state or configure an errdisable timeout.
Root guard allows the device to participate in STP as long as the device does not try to become the
root. If root guard blocks the port, subsequent recovery is automatic. Recovery occurs as soon as
the offending device ceases to send superior BPDUs.
This is the command for configuring root guard on an interface.
Switch(config-if)# spanning-tree guard root
To verify root guard, use the show spanning-tree inconsistentports command. Keep in mind
that a switch places a port in a root-inconsistent state if it receives BPDUs on a port that should not
be receiving BPDUs. The port recovers as soon as the offending BPDUs cease.

6.3.4 Configuring Storm Control
LAN storm attacks can be mitigated by using storm control to monitor predefined suppression-
level thresholds. When enabling storm control, both a rising threshold and a falling threshold can
be set.
Storm control uses one of these methods to measure traffic activity:

Bandwidth as a percentage of the total available bandwidth of the port that can be used by the

broadcast, multicast, or unicast traffic.
Traffic rate in packets per second at which broadcast, multicast, or unicast packets are

Traffic rate in bits per second at which broadcast, multicast, or unicast packets are received.

174 CCNA Security Course Booklet, Version 1.0

Traffic rate in packets per second and for small frames. This feature is enabled globally. The

threshold for small frames is configured for each interface.
With each method, the port blocks traffic when the predefined rising threshold is reached. The port
remains blocked until the traffic rate drops below the falling threshold if one is specified, and then
resumes normal forwarding. If the falling threshold is not specified, the switch blocks all traffic
until the traffic rate drops below the rising threshold. The threshold, or suppression level, refers to
the number of packets allowed before action is taken. In general, the higher the suppression level,
the less effective the protection against broadcast storms.
Use the storm-control interface configuration command to enable storm control on an interface
and set the threshold value for each type of traffic. The storm-control suppression level can be con-
figured as a percentage of total bandwidth of the port, as a rate in packets per second at which traf-
fic is received, or as a rate in bits per second at which traffic is received.
When the traffic suppression level is specified as a percentage (up to two decimal places) of the
total bandwidth, the level can be from 0.00 to 100.00. A threshold value of 100 percent means that
no limit is placed on the specified type of traffic (broadcast, multicast or unicast). A value of 0.0
means that all traffic of that type on that port is blocked.
Threshold percentages are approximations because of hardware limitations and the way in which
packets of different sizes are counted. Depending on the packet sizes that make up the incoming
traffic, the actual enforced threshold might differ from the configured level by several percentage
Storm control is supported on physical interfaces. With Cisco IOS Release 12.2(25), storm control
can also be configured on EtherChannels. When configuring storm control on an EtherChannel,
the storm control settings propagate to the EtherChannel physical interfaces.
This is the complete syntax for the storm-control command.
storm-control {{broadcast | multicast | unicast} level {level [level-low] | bps
bps [bps-low] | pps pps [pps-low]}} | {action {shutdown | trap}}
The trap and shutdown options are independent of each other.
If the trap action is configured, the switch will send an SNMP log message when a storm occurs.
If the shutdown action is configured, the port is error-disabled during a storm, and the no shut-
down interface configuration command must be used to bring the interface out of this state.

When a storm occurs and the action is to filter traffic, if the falling suppression level is not speci-
fied, the switch blocks all traffic until the traffic rate drops below the rising suppression level. If
the falling suppression level is specified, the switch blocks traffic until the traffic rate drops below
this level.
Use the show storm-control [interface] command to verify storm control settings. This com-
mand displays storm control suppression levels set on all interfaces, or the specified interface, for
the specified traffic type. If no traffic type is specified, the default is broadcast traffic.

6.3.5 Configuring VLAN Trunk Security
The best way to mitigate VLAN hopping attacks is to ensure that trunking is only enabled on ports
that require trunking. Additionally, be sure to disable DTP (auto trunking) negotiations and manu-
ally enable trunking.
To prevent a VLAN hopping attack that uses double 802.1Q encapsulation, the switch must look
further into the frame to determine whether more than one VLAN tag is attached to it. Unfortu-
nately, most switches have hardware that is optimized to look for one tag and then to switch the
Chapter 6: Securing the Local Area Network 175

frame. The issue of performance versus security requires administrators to balance their require-
ments carefully.
Mitigating VLAN hopping attacks that use double 802.1Q encapsulation requires several modifi-
cations to the VLAN configuration. One of the more important elements is to use a dedicated na-
tive VLAN for all trunk ports. This attack is easy to stop when following the recommended
practice of not using native VLANs for trunk ports anywhere else on the switch. In addition, dis-
able all unused switch ports and place them in an unused VLAN.
To control trunking for ports, several options are available.
For links that are not intended as trunks, use the switchport interface configuration
mode access
command to disable trunking.
There are three steps to create trunk links:
Step 1. Use the switchport interface configuration command to cause the interface
mode trunk
to become a trunk link.
Step 2. Use the switchport interface configuration command to prevent the genera-
tion of DTP frames.
Step 3. Use the switchport trunk native vlan vlan_number interface configuration command
to set the native VLAN on the trunk to an unused VLAN. The default native VLAN is VLAN 1.

6.3.6 Configuring Cisco Switched Port Analyzer
In addition to the mitigation techniques, it is also possible to configure a Layer 2 device to support
traffic analysis. Network traffic passing through ports or VLANs can be analyzed by using
switched port analyzer (SPAN) or remote SPAN (RSPAN). SPAN can send a copy of traffic from
one port to another port on the same switch where a network analyzer or monitoring device is con-
nected. RSPAN can send a copy of traffic to a port on a different switch. SPAN copies (or mirrors)
traffic received, sent, or both on source ports or source VLANs to a destination port for analysis.
SPAN does not affect the switching of network traffic on the source ports or VLANs. The destina-
tion port is dedicated for SPAN use. Except for traffic that is required for the SPAN or RSPAN ses-
sion, destination ports do not receive or forward traffic. Interfaces should usually be monitored in
both directions, while VLANs should be monitored in only one direction.
SPAN is not required for syslog or SNMP. SPAN is used to mirror traffic, while syslog and SNMP
are configured to send data directly to the appropriate server. SPAN does not mitigate attacks, but
it does enable monitoring of malicious activity.
A SPAN session can be configured to monitor source port traffic to a destination port. In this ex-
ample, the existing SPAN configuration for session 1 is deleted, and then bidirectional traffic is
mirrored from source Gigabit Ethernet port 0/1 to destination Gigabit Ethernet port 0/2, retaining
the encapsulation method.
Switch(config)# no monitor session 1
Switch(config)# monitor session 1 source interface gigabitethernet0/1
Switch(config)# monitor session 1 destination interface gigabitethernet0/2 encap-
sulation replicate
Switch(config)# end
Another example illustrates the capture of received and transmitted traffic for VLANs 10 and 20,
Switch(config)# monitor session 1 source vlan 10 rx
Switch(config)# monitor session 1 source vlan 20 tx
Switch(config)# monitor session 1 destination interface FastEthernet 3/4
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To verify SPAN configuration, use the show command.
monitor session session-number

An intrusion detection system (IDS) has the ability to detect misuse, abuse, and unauthorized ac-
cess to networked resources. SPAN can be used to mirror traffic to another port where a probe or
an IDS sensor is connected. When an IDS sensor detects an intruder, the sensor can send out a
TCP reset that tears down the intruder connection within the network, immediately removing the
intruder from the network.
SPAN is commonly deployed when an IDS is added to a network. IDS devices need to read all
packets in one or more VLANs, and SPAN can be used to get the packets to the IDS devices.

6.3.7 Configuring Cisco Remote Switched Port Analyzer
RSPAN has all the features of SPAN, plus support for source ports and destination ports that are
distributed across multiple switches, allowing one to monitor any destination port located on the
RSPAN VLAN. This allows an administrator to monitor the traffic on one switch using a device on
another switch.
RSPAN can be used to forward traffic to reach an IDS that is analyzing traffic for malicious behav-
ior. Source ports for the spanned traffic can be on multiple switches. If the purpose is intrusion de-
tection, the IDS examines the traffic forwarded by all the source devices. If an attacker
compromises the internal network through a perimeter router, a copy of the intruder traffic is for-
warded to the IDS for examination.
As with SPAN, RSPAN is not required for syslog or SNMP and is only used to mirror traffic, not
send data directly to a defined server. RSPAN does not mitigate attacks, but it does enable moni-
toring of malicious activity.
To configure RSPAN, start by configuring the RSPAN VLAN. Here, VLAN 100 is created and
configured as an RSPAN VLAN.
2960-1(config)# vlan 100
2960-1(config-vlan)# remote-span
2960-1(config-vlan)# exit
Next, it is necessary to configure the RSPAN source ports and VLANs. The traffic captured from
the source port is mirrored to a dedicated reflector port, which simply acts like a loopback inter-
face in that it reflects the captured traffic to the RSPAN VLAN. No traffic is actually sent out the
reflector port. It merely provides an internal loopback mechanism for RSPAN source sessions. A
reflector port exists only for an RSPAN source session. In this example, there is only one source
2960-1(config)# monitor session 1 source interface FastEthernet 0/1
2960-1(config)# monitor session 1 destination remote vlan 100 reflector-port
FastEthernet 0/24
2960-1(config)# interface FastEthernet 0/2
2960-1(config-if)# switchport mode trunk
Finally, configure the RSPAN traffic to be forwarded out an interface toward the IDS. In this ex-
ample, the traffic destined for VLAN 100 is forwarded out interface Fast Ethernet 0/2.
2960-2(config)# monitor session 2 source remote vlan 100
2960-2(config)# monitor session 2 destination interface FastEthernet 0/3
2960-2(config)# interface FastEthernet 0/2
2960-2(config-if)# switchport mode trunk
Use the show and show commands to verify RSPAN configuration.
monitor interfaces trunk

SPAN and RSPAN are used to mirror traffic for the purpose of protocol analysis or intrusion detec-
tion and prevention. A number of tools and technologies for securing the LAN infrastructure have
Chapter 6: Securing the Local Area Network 177

been explored. IronPort, NAC, and CSA secure the endpoints from various threats, including
buffer overflows, viruses, trojans, and worms. Technologies such as BPDU guard and root guard
work to prevent STP manipulation attacks. Storm control helps to prevent LAN storms. Port secu-
rity ensures that the proper hosts are attaching to switch ports. Layer 2 switching best practices
prevent VLAN attacks. But the modern LAN also includes wireless devices, IP telephony devices,
and storage area networking devices. These devices and the traffic associated with them need to be

6.3.8 Recommended Practices for Layer 2
Layer 2 guidelines are dependent on the particular security policy of an organization.
It is important to manage switches like routers, using secure protocols or out-of-band methods if
policy permits it. Turn off services that are not necessary and ports that are not being used. Imple-
ment various security services, such as port security and STP enhancements, as necessary and as
supported by the hardware. Turn Cisco Discovery Protocol (CDP) off on ports that do not connect
to network devices, with the exception of ports that connect to Cisco IP phones.
By default, VLAN 1 is the management VLAN. Also, by default, all ports are members of VLAN
1 (VLAN1 is the default user VLAN). In addition, VLAN1 is the default native VLAN for all
trunk ports. For this reason, it is strongly recommended that VLAN 1 not be used for anything. All
unused ports should be assigned to an unused VLAN. All trunk ports should be assigned to an un-
used dummy VLAN. The management VLAN should be assigned to an unused VLAN, not coin-
ciding with any user VLAN, the management VLAN, or the native VLAN.

6.4 Wireless, VoIP, and SAN Security
6.4.1 Enterprise Advanced Technology Security
Wireless LAN technology has been a powerful driver for advances in network security. With
greater ease of access via wireless devices comes a greater need for comprehensive wireless secu-
rity solutions.
Similarly, the advent of Voice over IP (VoIP) and all the accompanying devices and technologies
(IP telephony), has motivated several advances in security. Who would want their telephone call
intercepted by a hacker? It is worthwhile to describe the drivers for VoIP implementations, the
components that are required in VoIP networks, and VoIP service issues. The natural progression is
to explore the implications of implementing security measures in IP networks that transport voice.
Storage area networks (SANs) offer a solution to the increasing cost of network and server down-
time. Given that the purpose of network security is to secure data (including voice and video), and
the fact that data now typically resides on a SAN, it is essential that the SAN be secured.
Modern enterprise networks typically employ wireless controllers, access points, and a wireless
management system to deliver comprehensive protection against wireless attacks. The wireless en-
vironment is secured with infrastructure-integrated threat protection, advanced visibility into the
RF environment, and wired network security collaboration.
An infrastructure-integrated approach to comprehensive wireless security reduces costs while
streamlining security operations. Such a solution has a number of benefits:

Proactive threat and intrusion detection capabilities detect wireless attacks and prevent them.

178 CCNA Security Course Booklet, Version 1.0

Comprehensive protection safeguards confidential data and communications.

A single user identity and policy simplifies user management and protects against

unauthorized access.
Collaboration with wired security systems enables a superset of wireless security functionality

and protection.

IP phones, IP Private Branch Exchanges (PBXs), voice gateways, voice mail systems, and the req-
uisite protocols are also common in an enterprise network. These technologies and protocols en-
hance productivity and ultimately save the organization on telephony costs. By using an IP PBX,
organizations can eliminate the legacy PBX and enjoy IP telephony benefits over a converged net-
work. An IP PBX provides call-control functionality and, when used in conjunction with IP phone
sets or a soft phone application, it can provide PBX functionality in a distributed and scalable fash-
ion. Cisco IP telephony solution deployment models fall into one of these categories:

Single-site deployment

Centralized call processing with remote branches

Distributed call processing deployment

Clustering over the IP WAN

Selection of the deployment model depends on the organization™s requirements, such as the size of
the network, features, and availability of the WAN bandwidth.
Enterprise networks also utilize storage area networking. Storage networking is central to the con-
temporary data center architecture, providing a networking platform that helps IT departments
achieve lower total cost of ownership, enhanced resiliency, and greater agility. Storage network so-
lutions provide:

Investment protection - First, second, and third generations can all coexist in existing

customer chassis and new switch configurations.
Virtualization - IT managers can provision their storage infrastructure.

Security - Data is protected when it is at rest and while it is being transported and replicated.

Consolidation - Storage professionals can consolidate resources by taking advantage of

highly scalable, intelligent SAN platforms.
Availability - Instantaneous access to data is available from multiple tiers for disaster


Wireless LANs rely on radio frequency (RF) technology. RF technology has existed since the late
nineteenth century. VoIP technology became commercially available in the 1990s. SAN technol-
ogy did not formally enter the market until the early 2000s. The approach here follows the histori-
cal order.

6.4.2 Wireless Security Considerations
In the early 2000s, the autonomous access point (AP) deployment model was quickly replaced by
the lightweight access point deployment model. Lightweight APs depend on wireless LAN con-
trollers (WLCs) for their configurations. This differs from autonomous APs, which require individ-
ual configuration of each device. The lightweight AP-wireless controller solution has several
benefits that were not previously available, such as rogue AP detection and location.
Chapter 6: Securing the Local Area Network 179

Cisco WLCs are responsible for system-wide wireless LAN functions, such as security policies,
intrusion prevention, RF management, QoS, and mobility. These functions work in conjunction
with APs and the Cisco Wireless Control System (WCS) to support wireless applications. From
voice and data services to location tracking, Cisco WLCs provide the control, scalability, security,
and reliability to build secure, enterprise-scale wireless networks from branch offices to main cam-
Cisco WLCs smoothly integrate into existing enterprise networks. They communicate with light-
weight APs over any Layer 2 or Layer 3 infrastructure using the Lightweight Access Point Proto-
col (LWAPP). These devices support automation of numerous WLAN configuration and
management functions across all enterprise locations.
Because the Cisco WLCs support IEEE 802.11a/b/g and the 802.11n standards, organizations can
deploy the solution that best meets their individual requirements. Organizations can offer robust
coverage with 802.11a/b/g or deliver greater performance with five times the throughput and the
increased reliability of 802.11n.
With pervasive wireless Internet access available, hackers now have expanded opportunities to
covertly connect to remote networks. Whether a skilled hacker or a novice to wireless technology,
opportunities abound for exploiting weaknesses in wireless networks.
The most popular form of wireless hacking is called war driving, where a hacker attempts to gain
access to wireless networks on their laptop while driving around a metropolitan or suburban area.
A neighbor might hack into another neighbor™s wireless network to get free Internet access or to
access confidential information. Airports, fast food restaurants, and coffee shops frequently offer
Internet access, which again gives hackers the opportunity to compromise the data of other users.
A hacker might even try to connect to another computer using ad hoc mode in a public area.
It is never safe to connect to an open wireless network, especially in a public area, unless the con-
nection is followed by an encrypted VPN connection to another network. With respect to the enter-
prise network, remember that most security attacks come from the inside. These attacks can be
intentionally launched by a disgruntled employee, or they might be unintentionally activated by a
computer that is infected by a virus. Many organizations, as part of their security policies, do not
allow employees to install their own APs in the worksite.
Wireless hackers have an array of tools at their disposal, depending on their level of sophistication
and determination:

Network Stumbler software finds wireless networks.

Kismet software displays wireless networks that do not broadcast their SSIDs.

AirSnort software sniffs and cracks WEP keys.

CoWPAtty cracks WPA-PSK (WPA1).

ASLEAP gathers authentication data.

Wireshark can scan wireless Ethernet data and 802.11 SSIDs.

For the more determined hacker, a spectrum analyzer can be used to identify, classify, and find
sources of Wi-Fi RF signals. Modern spectrum analyzers can identify the specific types of devices
that are causing RF interference and track them to their physical location.

6.4.3 Wireless Security Solutions
The first wireless LANs (WLANs) emerged in 1990. These WLANs were totally open, with no au-
thentication or encryption required. The first security option for WLANs was a service set identi-
180 CCNA Security Course Booklet, Version 1.0

fier (SSID). Later implementations enabled the use of SSIDs without the APs broadcasting the
The IEEE 802.11b standard defined the Wired Equivalent Privacy (WEP) security protocol for en-
crypting data between radio endpoints. For several years, WEP implementations were the only
means for securing WLANs. Weaknesses in WEP led to the development of newer technologies,
based on protocols such as Temporal Key Integrity Protocol (TKIP) and ciphers such as Advanced
Encryption Standard (AES). Wi-Fi Protected Access (WPA) implements TKIP and is more secure
than WEP. WPA2 implements AES and is more secure than WPA. WPA2, an interoperable imple-
mentation of 802.11i, is currently the state of the art in wireless security.
Along the way, authentication was added as an option to securing WLANs and is now a fundamen-
tal component of enterprise wireless policy. The 802.11i architecture specifies 802.1X for authen-
tication, entailing the use of EAP and an authentication server.
When designing and using wireless networks, it is a good idea for the network security profes-
sional to maintain an appropriate level of paranoia. Wireless networks are extremely inviting to
Fortunately, if a few precautions are taken, network administrators can decrease the risk for wire-
less users. The network administrator should keep several security considerations in mind:

Wireless networks using WEP or WPA/TKIP are not very secure and are vulnerable to

hacking attacks.
Wireless networks using WPA2/AES should have a pass phrase of at least 21 characters.

If an IPsec VPN is available, use it on any public wireless LAN.

If wireless access is not needed, disable the wireless radio or wireless NIC.

As a network security professional, deploying a wireless solution should absolutely require
WPA2/AES together with authentication. Authentication should be handled by a centralized au-
thentication server.

6.4.4 VoIP Security Considerations
VoIP is the transmission of voice traffic over IP-based networks. IP was originally designed for
data networking, but its success in data networking has led to its adaptation to voice traffic.
VoIP has become popular largely because of the cost savings over traditional telephone networks.
On traditional telephone networks, most people pay a flat monthly fee for local telephone calls and
a per-minute charge for long-distance calls. VoIP calls are placed using the Internet, with most In-
ternet connections being charged a flat monthly fee. Using the Internet connection for both data
traffic and voice calls allows consumers to reduce their monthly phone bill. For international calls,
the monetary savings can be enormous.
The business advantages that drive implementations of VoIP networks have changed over time.
Starting with simple media convergence, these advantages have evolved to include the conver-
gence of call-switching intelligence and the total user experience. Originally, return on investment
(ROI) calculations centered on toll-bypass and converged-network savings. Although these savings
are still relevant today, advances in voice technologies allow organizations and service providers to
differentiate their product offerings by providing advanced features.
VoIP has a number of business advantages:

Lower telecom call costs are significant. VoIP service providers charge up to 50 percent less

for phone connectivity service.
Chapter 6: Securing the Local Area Network 181

Productivity increases with VoIP phone service can be substantial. Some businesses have

reported productivity increases of up to three hours per week, per employee. Features such as
find me/follow me, remote office, click-to-call, Outlook integration, unified voice mail,
conference calling, and collaboration tools enable productivity increases.
Move, add, and change costs are much lower. VoIP flexibility enables easily moving a phone

between workstations.
Ongoing service and maintenance costs can be lower.

Many VoIP systems require little or no training for users.

Mobile phone charges decrease as employees make calls via their laptop instead of their

mobile phone. These network calls are part of the network charges and cost only the amount
of the Internet connection itself.
Telecommuting phone costs are decreased and there are no major setup fees. Voice

communication takes place over a broadband connection.
VoIP enables unified messaging. Information systems are integrated.

Encryption of voice calls is supported.

Fewer administrative personnel are needed for answering telephones.

A packet voice network, or network that supports voice traffic, has a number of components:

IP phones - Provide IP voice to the desktop.

Gatekeeper - Provides Call Admission Control (CAC), bandwidth control and management,

and address translation.
Gateway - Provides translation between VoIP and non-VoIP networks, such as the PSTN.

Gateways also provide physical access for local analog and digital voice devices, such as
telephones, fax machines, key sets, and PBXs.
Multipoint control unit (MCU) - Provides real-time connectivity for participants in multiple

locations to attend the same videoconference or meeting.
Call agent - Provides call control for IP phones, CAC, bandwidth control and management,

and address translation. Cisco Unified Communications Managers and Cisco Unified
Communications Manager Business Edition both function as the call agents.
Application servers - Provide services such as voice mail and unified messaging, such as

Cisco Unity.
Videoconference station - Provides access for end-user participation in videoconferencing.

The videoconference station contains a video capture device for video input and a microphone
for audio input. The user can view video streams and hear the audio that originates at a remote
user station.
Other components, such as software voice applications, interactive voice response (IVR) systems,
and softphones, provide additional services to meet the needs of enterprise sites.
VoIP depends on a number of specialized protocols, including H.323, Media Gateway Control
Protocol (MGCP), Session Initiation Protocol (SIP), skinny call control protocol (SCCP), and real-
time protocol RTP.
VoIP communication occurs over the traditional data network. That means that securing voice
communication is directly related to securing the data network. There are several threats specific to
VoIP networks.
182 CCNA Security Course Booklet, Version 1.0

Unauthorized access to voice resources
Hackers can tamper with voice systems, user identities, and telephone configurations, and inter-
cept voice-mail messages. If hackers gain access to the voice-mail system, they can change the
voice-mail greeting, which can have a negative impact on the image and reputation of the com-
pany. A hacker who gains access to the PBX or voice gateway can shut down voice ports or change
voice-routing parameters, affecting voice access into and through the network.
Compromising network resources
The goal of a secure network is to ensure that applications, processes, and users can reliably and
securely interoperate using the shared network resources. Because the shared network infrastruc-
ture carries voice and data, security and access to the network infrastructure are critical in securing
voice functions. Because IP voice systems are installed on a data network, they are potential tar-
gets for hackers who previously targeted only PCs, servers, and data applications. Hackers are
aided in their search for vulnerabilities in IP voice systems by the open and well-known standards
and protocols that are used by IP networks.
Eavesdropping involves the unauthorized interception of voice packets or RTP media streams.
Eavesdropping exposes confidential or proprietary information that is obtained by intercepting and
reassembling packets in a voice stream. Hackers use a variety of tools to eavesdrop.
DoS attacks
DoS attacks are defined as the malicious attacking or overloading of call-processing equipment to
deny access to services by legitimate users. Most DoS attacks fall into one of three categories:

Network resource overload involves overloading a network resource that is required for

proper functioning of a service. The network resource is most often bandwidth. The DoS
attack uses up all available bandwidth, causing authorized users to be unable to access the
required services.
Host resource starvation involves using up critical host resources. When use of these

resources is maximized by the DoS attack, the server can no longer respond to legitimate
service requests.
Out-of-bounds attack involves using illegal packet structure and unexpected data, which can

cause the operating system of the remote system to crash. One example of this type of attack
is using illegal combinations of TCP flags. Most TCP/IP stacks are developed to respond to
appropriate use; they are not developed for anomalies. When the stack receives illegal data, it
might not know how to handle the packet, causing a system crash.
VoIP spam, or SPIT, is unsolicited and unwanted bulk messages broadcast over VoIP to the end
users of an enterprise network. In addition to being annoying, high-volume bulk calls can signifi-
cantly affect the availability and productivity of the endpoints. Because bulk calls are also difficult
to trace, they can be used for fraud, unauthorized use, and privacy violations.
Up to now, VoIP spam is infrequent, but it has the potential to become a major problem. SPIT
could be generated in a similar way to email spam with botnets targeting millions of VoIP users
from compromised machines.
Spam has been a problem for years. Unsolicited commercial and malicious email spam now makes
up the majority of email worldwide. For example, in Europe, according to analysts Radicati, 16
billion spam messages were sent each day in 2006, representing 62 percent of all European email
messages. This figure is expected to increase to 37 billion spam emails a day by 2010. There is
concern that VoIP will suffer the same fate as email.
Chapter 6: Securing the Local Area Network 183

Another concern about SPIT is that email anti-spam methods will not work. The real-time nature
of voice calls makes dealing with SPIT much more challenging than email spam. New methods
have to be invented to address SPIT problems.
Authenticated Transport Layer Security (TLS) stops most SPIT attacks, because endpoints only
accept packets from trusted devices.
Two common types of fraud in VoIP networks are vishing and toll fraud.
Vishing (voice phishing) uses telephony to glean information, such as account details directly from
users. One of the first reported cases of vishing affected PayPal. Victims first received an email
pretending to come from PayPal asking them to verify their credit card details over the phone.
Those who called the number were then asked to enter their credit card number using the keypad.
After the credit card number had been entered, the perpetrators of this fraud were able to steal
money from the account of their victims.
Because of the lower cost of making VoIP calls as compared to standard phone systems, attackers
can call thousands of people for very little cost. Users still trust the telephone more than the web,
but these spamming techniques can undermine user confidence in VoIP.
Toll fraud is the theft of long-distance telephone service by unauthorized access to a PSTN trunk
(an outside line) on a PBX or voice-mail system. Toll fraud is a multibillion-dollar illegal industry,
and all organizations are vulnerable. Theft can also be defined as the use of the telephony system
by both authorized and unauthorized users to access unauthorized numbers, such as premium rate
This fraud is not new and PBXs have always been vulnerable. The difference is that few people
could hack into PBXs, compared to the numbers of people actively breaking into IP systems. To
protect against such fraud, network administrators use features that exist in Cisco Unified Commu-
nications Manager to control phone calls, such as dial plan filters, partitions, or Forced Authoriza-
tion Codes (FACs).
Another growing VoIP security issue concerns SIP. The increasing adoption of SIP for VoIP is ex-
pected to open up a completely new front in the security war. SIP is a relatively new protocol that
offers little inherent security. Some of its characteristics also leave it vulnerable to hackers, such as
using text for encoding and SIP extensions that can create security holes.
Examples of hacks for SIP include registration hijacking, which allows a hacker to intercept in-
coming calls and reroute them; message tampering, which allows a hacker to modify data packets
traveling between SIP addresses; and session tear-down, which allows a hacker to terminate calls
or carry out a VoIP-targeted DoS attack by flooding the system with shutdown requests.

6.4.5 VoIP Security Solutions
Many IP security solutions can be implemented only on Layer 3 devices. Because of protocol ar-
chitecture, Layer 2 offers very little or no inherent security. Understanding and establishing broad-
cast domains is one of the fundamental concepts in designing secure IP networks. Many simple yet
dangerous attacks can be launched if the attacking device resides within the same broadcast do-
main as the target system. For this reason, IP phones, VoIP gateways, and network management
workstations should always be on their own subnet, separate from the rest of the data network and
from each other.
To ensure communications privacy and integrity, voice media streams must be protected from
eavesdropping and tampering. Data-networking technologies such as VLANs can segment voice
traffic from data traffic, preventing access to the voice VLAN from the data VLAN. Using separate
184 CCNA Security Course Booklet, Version 1.0

VLANs for voice and data prevents any attacker or attacking application from snooping or captur-
ing other VLAN traffic as it traverses the physical wire. By making sure that each device connects
to the network using a switched infrastructure, packet-sniffing tools can also be rendered less ef-
fective for capturing user traffic.
Assigning voice traffic to specific VLANs to logically segment voice and data traffic is an indus-
try-wide recommended practice. As much as possible, devices that are identified as voice devices
should be restricted to dedicated voice VLANs. This approach ensures that they can communicate
only with other voice resources. More importantly, voice traffic is kept away from the general data
network, where it could be more easily intercepted or tampered with. Having a voice-specific
VLAN makes it easier to apply VLAN access control lists (VACLs) to protect voice traffic.
By understanding the protocols that are used between devices in the VoIP network, effective ACLs
can be implemented on the voice VLANs. IP phones send only RTP traffic to each other, and they
never have a reason to send TCP or ICMP traffic to each other. IP phones do send a few TCP and
UDP protocols to communicate with servers. Many of the IP phone attacks can be stopped by
using ACLs on the voice VLANs to prevent deviations from these principles.
Firewalls inspect packets and match them against configured rules based on the ports specified. It
is difficult to specify in advance which ports will be used in a voice call because the ports are dy-
namically negotiated during call setup.
Cisco ASA Adaptive Security Appliances inspect voice protocols to ensure that SIP, SCCP, H.323,
and MGCP requests conform to voice standards. Cisco ASA Adaptive Security Appliances can
also provide these capabilities to help protect voice traffic:

Ensure SIP, SCCP, H.323, and MGCP requests conform to standards.

Prevent inappropriate SIP methods from being sent to Cisco Unified Communications

Rate limit SIP requests.

Enforce the policy of calls (whitelist, blacklist, caller/called party, SIP Uniform Resource

Dynamically open ports for Cisco applications.

Enable only “registered phones” to make calls.

Enable inspection of encrypted phone calls.

Cisco IOS firewalls also provide many of these secure features.
VPNs are widely used to provide secure connections to the corporate network. The connections
can originate from a branch office, a small office/home office (SOHO), a telecommuter, or a roam-
ing user. IPsec can be used for authentication and confidentiality services. To facilitate perform-
ance, it is recommended that VPN tunnels terminate inside of a firewall. The firewall is used to
inspect and protect the plaintext protocols.
When deploying VPNs across the Internet or a public network, it is important to consider the ab-
sence of QoS. Where possible, QoS should be addressed with the provider through a service level
agreement (SLA). An SLA is a document that details the expected QoS parameters for packets that
go through the provider network.
Voice communications do not work well (or sometimes at all) with latency. Because secure VPNs
encrypt data, they can create a throughput bottleneck when they process packets through their en-
cryption algorithm. The problem usually gets worse as security increases.
Chapter 6: Securing the Local Area Network 185

VoIP and either DES or 3DES encryptions are fully compatible with each other as long as the VPN
delivers the necessary throughput. Internationally, corporations might face other issues that affect
voice communications. The U.S. Department of Commerce places restrictions on the export of cer-
tain encryption technology. Usually, DES is exportable while 3DES is not. However, regulations
take numerous forms, from total export exclusions that are applied to certain countries, to allowing
3DES export to specific industries and users. Most corporations with VPNs that extend outside the
United States must find out if their VPN provider has exportable products and how export regula-
tions affect networks built with those products.
When securing voice traffic, do not forget to secure the voice application servers. The newer ver-
sions of Cisco Unified Communications Manager disable unnecessary services, disable default
usernames, allow only signed images to be installed, have CSA installed, and support secure man-
agement protocols.
By combining the transport security that is provided by secure LANs, firewalls, and VPNs with the
application and host security features available with the Cisco Unified Communications Manager
and Cisco IP phones, it is possible to have a highly secure IP telephony environment.

6.4.6 SAN Security Considerations
A SAN is a specialized network that enables fast, reliable access among servers and external stor-
age resources. In a SAN, a storage device is not the exclusive property of any one server. Rather,
storage devices are shared among all networked servers as peer resources. Just as a LAN can be
used to connect clients to servers, a SAN can be used to connect servers to storage, servers to each
other, and storage to storage.
A SAN does not need to be a physically separate network. It can be a dedicated subnet that carries
only business-critical I/O traffic between servers and storage devices. A SAN, for example, would
not carry general-purpose traffic such as email or other end-user applications. It would be limited
to I/O traffic, such as reading a file from a disk or writing a file to a disk. This network approach
helps avoid the unacceptable compromise and reduced performance that is inherent when a single
network is used for all applications.
Network and server downtime costs companies large sums of money in business and productivity
losses. At the same time, the amount of information to be managed and stored is increasing dra-
matically every year.
SANs offer an answer to the increasing volume of data that must be stored in an enterprise net-
work environment. By implementing a SAN, users can offload storage traffic from the daily net-
work operations and establish a direct connection between storage media and servers.
SANs in enterprise infrastructures are evolving rapidly to meet three primary business require-

Reduce capital and operating expenses.

Increase agility to support changing business priorities, application requirements, and revenue

Improve long-distance replication, backup, and recovery to meet regulatory requirements and

industry best practices.
Cisco provides an enterprise-wide approach to deploying scalable, highly available, and more eas-
ily administered SANs. Cisco solutions for intelligent SANs are an integral part of an enterprise
data center architecture. Cisco SAN solutions provide a preferred means of accessing, managing,
and protecting information resources across a variety of SAN transport technologies. These in-
186 CCNA Security Course Booklet, Version 1.0

clude consolidated Fibre Channel, Fibre Channel over IP (FCIP), Internet Small Computer Sys-
tems Interface (iSCSI), Gigabit Ethernet, or optical network.
All the major SAN transport technologies are based on the SCSI communications model. In many
ways, a SAN can be described as the merging of SCSI and networking. SCSI command protocol is
the de facto standard that is used extensively in high-performance storage applications. The com-
mand part of SCSI can be transported over a Fibre Channel SAN or encapsulated in IP and carried
across IP networks.
There are three major SAN transport technologies:

Fibre Channel - This technology is the primary SAN transport for host-to-SAN connectivity.

Traditionally, SANs have required a separate dedicated infrastructure to interconnect hosts
and storage systems. The primary transport protocol for this interconnection has been Fibre
Channel. Fibre Channel networks provide a serial transport for the SCSI protocol.
iSCSI - Maps SCSI over TCP/IP. This is another host-to-SAN connectivity model that is

typically used in the LAN. An iSCSI leverages an investment in existing IP networks to build
and extend the SANs. This is accomplished by using TCP/IP to transport SCSI commands,
data, and status between hosts or initiators and storage devices or targets, such as storage
subsystems and tape devices.
FCIP - Popular SAN-to-SAN connectivity model that is often used over the WAN or MAN

(metropolitan area network). SAN designers can use the open-standard FCIP protocol to break
the distance barrier of current Fibre Channel solutions and enable interconnection of SAN
islands over extended distances.

In computer storage, a logical unit number (LUN) is a 64-bit address for an individual disk drive
and, by extension, the disk device itself. The term is used in the SCSI protocol as a way to differ-
entiate individual disk drives within a common SCSI target device such as a disk array.
LUN masking is an authorization process that makes a LUN available to some hosts and unavail-
able to other hosts. LUN masking is implemented primarily at the host bus adapter (HBA) level.
LUN masking that is implemented at this level is vulnerable to any attack that compromises the
The security benefits of LUN masking are limited because, with many HBAs, it is possible to
forge source addresses. LUN masking is mainly a way to protect against misbehaving servers cor-
rupting disks belonging to other servers.
For example, Windows servers that are attached to a SAN sometimes corrupt non-Windows vol-
umes by attempting to write Windows volume labels to them. By hiding the LUNs of the non-Win-
dows volumes from the Windows server, this can be prevented because the Windows server does
not even realize the non-Windows volumes exist.
Today, LUNs are normally not individual disk drives but virtual partitions (or volumes) of a Re-
dundant Array of Independent Disks (RAID) set.
A world wide name (WWN) is a 64-bit address that Fibre Channel networks use to uniquely iden-
tify each element in a Fibre Channel network.
Zoning can utilize WWNs to assign security permissions. Zoning can also use name servers in the
switches to either allow or block access to particular WWNs in the fabric.
The use of WWNs for security purposes is inherently insecure, because the WWN of a device is a
user-configurable parameter. Zoning that uses WWNs is susceptible to unauthorized access, be-
cause the zone can be bypassed if an attacker is able to spoof the WWN of an authorized host bus
Chapter 6: Securing the Local Area Network 187

adapter (HBA). An HBA is an I/O adapter that sits between the bus of the host computer and the
Fibre Channel loop and manages the transfer of information between the two channels.
In storage networking, Fibre Channel zoning is the partitioning of a Fibre Channel fabric into
smaller subsets. If a SAN contains several storage devices, one device should not necessarily be al-
lowed to interact with all the other devices in the SAN.
Zoning is sometimes confused with LUN masking, because both processes have the same objec-
tives. The difference is that zoning is implemented on fabric switches while LUN masking is per-
formed on endpoint devices. Zoning is also potentially more secure. Zone members see only other
members of the zone. Devices can be members of more than one zone.
There are some simple rules to keep in mind for zoning operation:

Zone members see only other members of the zone.

Zones can be configured dynamically based on WWN.

Devices can be members of more than one zone.

Switched fabric zoning can take place at the port or device level, based on the physical switch

port, device WWN, or LUN ID.
Fibre Channel fabric zoning has the benefit of securing device access and allowing operating sys-
tem coexistence. Zoning applies only to the switched fabric topology; it does not exist in simpler
Fibre Channel topologies.
A virtual storage area network (VSAN) is a collection of ports from a set of connected Fibre
Channel switches that form a virtual fabric. Ports can be paritioned within a single switch into
multiple VSANs. Additionally, multiple switches can join any number of ports to form a single
VSAN. In this manner, VSANs strongly resemble VLANs. Like VLANs, traffic is tagged as it
crosses inter-switch links with the VSAN ID.
Fabric events are isolated per VSAN. VSANs utilize hardware-based isolation, meaning that traffic
is explicitly tagged across inter-switch links with VSAN membership information. Statistics can
also be gathered on a per-VSAN basis.
VSANs were originally invented by Cisco, but they have now been adopted as an ANSI standard.

6.4.7 SAN Security Solutions
In order to secure SANs, it is necessary to secure the SAN fabric, any attaching hosts, and the ac-
tual disks.
There are six critical areas to consider when securing a SAN:

SAN management - Secure the management services that are used to administer the SAN.

Fabric access - Secure access to the fabric. The SAN fabric refers to the hardware that

connects servers to storage devices.
Target access - Secure access to storage devices (targets) and LUNs.

SAN protocols - Secure the protocols that are used in switch-to-switch communication.

IP storage access - Secure FCIP and iSCSI.

Data integrity and secrecy - Encrypt data as it crosses networks as well as when stored on

188 CCNA Security Course Booklet, Version 1.0

There are several types of SAN-management tools available that can manage device-level per-
formance and application-level performance, as well as offer reporting and monitoring of services.
Whatever SAN-management tool is used, ensure that access to the management tool is secure.
When managing a SAN, there are other security concerns to consider:

Disruption of switch processing - A DoS attack can cause excessive load on the CPU,

rendering the CPU unable to react to fabric events.
Compromise of fabric - Changed configurations or lost configurations can result in changes

to the configured services or ports.
Compromise of data integrity and confidentiality - Breaching the actual data compromises

the integrity and confidentiality of stored information.
To ensure application data integrity, LUN integrity, and application performance, it is necessary to
secure both fabric and target access.
If fabric and target access are not secure, this can result in unauthorized access to data. Unautho-
rized access means that integrity and confidentiality have both been breached. Data may also be
corrupted or deleted. If the LUN is compromised either accidentally or intentionally, data can be
lost and availability can be threatened. Finally, application performance and availability can be af-
fected by unnecessary I/O or fabric events because the processor is kept busier than required.
To prevent these types of issues, use VSANs and zoning.
VSANs and zones are complementary technologies that work well together as a security control in
a SAN. The first step in configuring these complimentary protocols is to associate the physical
ports with a VSAN, much like associating switch ports with VLANs, and then logically dividing
the VSANs into zones.
Zoning is the prime mechanism for securing access to SAN targets (disk and tape). There are two
main methods of zoning, hard and soft. Soft zoning restricts the fabric name services, showing a
device only an allowed subset of devices. When a server looks at the content of the fabric, it sees
only the devices that it is allowed to see. However, any server can still attempt to contact other de-
vices on the network based on their addresses.
In contrast, hard zoning restricts communication across a fabric. This zoning is more commonly
used because it is more secure.
To secure data during transmission, a number of techniques are employed. iSCSI leverages many
strategies that are common to IP networking. For example, IP ACLs are analogous to Fibre Chan-
nel zones, VLANs are similar to VSANs, and IEEE 802.1X port security resembles Fibre Channel
port security.
For data transmission security, a number of encryption and authentication protocols are supported:

Diffie-Hellman Challenge Handshake Authentication Protocol (DH-CHAP)

Fibre Channel Authentication Protocol (FCAP)

Fibre Channel Password Authentication Protocol (FCPAP)

Encapsulating Security Payload (ESP)

Fibre Channel Security Protocol (FC-SP)

Chapter 6: Securing the Local Area Network 189

FCIP security leverages many IP security features in Cisco IOS-based routers:

IPsec for security over public carriers

High-speed encryption services in specialized hardware

Firewall filtering

Securing SANs completes the process of securing the LAN: secure the endpoints, the switches, the
wireless environment, the VoIP infrastructure, and the SANs.
In securing the LAN, a number of references to IPsec have been made. IPsec is a means of en-
crypting data between endpoints, such as within a VPN tunnel. To understand how IPsec works, a
basic understanding of cryptography is necessary.
190 CCNA Security Course Booklet, Version 1.0

Chapter Summary
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for this chapter for this chapter

Your Chapter Notes
Chapter 6: Securing the Local Area Network 191
192 CCNA Security Course Booklet, Version 1.0

Cryptographic Systems

Chapter Introduction
A network can be secured through device hardening, AAA access control, firewall features, and
IPS implementations. These combined features protect the infrastructure devices as well as the end
devices within the local network. But how is network traffic protected when traversing the public
Internet? The answer is through cryptographic methods.
Cryptology is the science of making and breaking secret codes. The development and use of codes
is called cryptography, and breaking codes is called cryptanalysis. Cryptography has been used for
centuries to protect secret documents. For example, Julius Caesar used a simple alphabetic cipher
to encrypt messages to his generals in the field. His generals would have knowledge of the cipher
key required to decrypt the messages. Today, modern day cryptographic methods are used in mul-
tiple ways to ensure secure communications.
Secure communication requires a guarantee that the message is not a forgery and does actually
come from whom it states (authentication). It also requires a guarantee that no one intercepted the
message and altered it (integrity). Finally, secure communication ensures that if the message is
captured, it cannot be deciphered (confidentiality).
The principles of cryptology can be used to explain how modern day protocols and algorithms are
used to secure communications. Many modern networks ensure authentication with protocols such
as HMAC. Integrity is ensured by implementing either MD5 or SHA-1. Data confidentiality is en-
sured through symmetric encryption algorithms, including DES, 3DES, and AES, or asymmetric
algorithms, including RSA and the public key infrastructure (PKI). Symmetric encryption algo-
rithms are based on the premise that each communicating party knows the pre-shared key. Asym-
metric encryption algorithms are based on the assumption that the two communicating parties have
not previously shared a secret and must establish a secure method to do so.
In a hands-on lab for the chapter, Exploring Encryption Methods, learners decipher a pre-en-
crypted message using the Vigenere cipher, create and decipher a Vigenere cipher message, and
use steganography to embed a secret message in a graphic. The lab is found in the lab manual on
Academy connection at cisco.netacad.net.

7.1 Cryptographic Services
7.1.1 Securing Communications
The first goal for network administrators is to secure the network infrastructure, including routers,
switches, servers, and hosts. This is accomplished using hardening, AAA access control, ACLs,
firewalls, and monitoring threats using IPS.
The next goal is to secure the data as it travels across various links. This may include internal traf-
fic, but of greater concern is protecting the data that travels outside of the organization to branch
sites, telecommuter sites, and partner sites.
194 CCNA Security Course Booklet, Version 1.0

Secure communications involves a few primary tasks:

Authentication - Guarantees that the message is not a forgery and does actually come from

who it states it comes from.
Integrity - Similar to a checksum function in a frame, guarantees that no one intercepted the

message and altered it.
Confidentiality - Guarantees that if the message is captured, it cannot be deciphered.

Authentication guarantees that a message comes from the source that it claims to come from. Au-
thentication is similar to entering a secure personal information number (PIN) for banking at an
ATM. The PIN should only be known to the user and the financial institution. The PIN is a shared
secret that helps protect against forgeries.
Authentication can be accomplished with cryptographic methods. This is especially important for
applications or protocols, such as email or IP, that do not have built-in mechanisms to prevent
spoofing of the source.
Data nonrepudiation is a similar service that allows the sender of a message to be uniquely identi-
fied. With nonrepudiation services in place, a sender cannot deny having been the source of that
message. It might appear that the authenticity service and the nonrepudiation service are fulfilling
the same function. Although both address the question of the proven identity of the sender, there is
a difference between the two.
The most important part of nonrepudiation is that a device cannot repudiate, or refute, the validity
of a message sent. Nonrepudiation relies on the fact that only the sender has the unique character-
istics or signature for how that message is treated. Not even the receiving device can know how the
sender treated this message to prove authenticity, because the receiver could then pretend to be the
On the other hand, if the major concern is for the receiving device to validate the source and there
is no concern about the receiving device imitating the source, it does not matter that the sender and
receiver both know how to treat a message to provide authenticity. An example of authenticity ver-
sus nonrepudiation is a data exchange between two computers of the same company versus a data
exchange between a customer and an e-commerce website. The two computers within the organi-
zation that exchange data do not have to prove to the other which of them sent a message. The
only thing that must be proven is that whatever was received by one was sent by the other. In this
instance, the two computers can share the same way of transforming their messages.
This practice is not acceptable in business applications, such as when purchasing items online
through a web shop. If the web shop knows how a customer transforms messages to prove authen-
ticity of the source, the web shop could easily fake “authentic” orders. In such a scenario, the
sender must be the only party having the knowledge of how to transform messages. The web shop
can prove to others that the order was, in fact, sent by the customer, and the customer cannot argue
that the order is invalid.
Data integrity ensures that messages are not altered in transit. With data integrity, the receiver can
verify that the received message is identical to the sent message and that no manipulation oc-
European nobility ensured the data integrity of documents by creating a wax seal to close an enve-
lope. The seal was often created using a signet ring. These bore the family crest, initials, a portrait,
Chapter 7: Cryptographic Systems 195

or a personal symbol or motto of the owner of the signet ring. An unbroken seal on an envelope
guaranteed the integrity of its contents. It also guaranteed authenticity based on the unique signet
ring impression.
Data confidentiality ensures privacy so that only the receiver can read the message. Encryption is
the process of scrambling data so that it cannot be read by unauthorized parties.
When enabling encryption, readable data is called plaintext, or cleartext, while the encrypted ver-
sion is called ciphertext. The plaintext readable message is converted to ciphertext, which is the
unreadable, disguised message. Decryption reverses the process. A key is required to encrypt and
decrypt a message. The key is the link between the plaintext and ciphertext.
Historically, various encryption algorithms and methods have been used. Julius Caesar is said to
have secured messages by putting two sets of the alphabet side by side and then shifting one of
them by a specific number of places. The number of places in the shift serves as the key. He con-
verted plaintext into ciphertext using this key, and only his generals, who also had the key, knew
how to decipher the messages. This method is now known as the Caesar cipher.
Using a hash function is another way to ensure data confidentiality. A hash function transforms a
string of characters into a usually shorter, fixed-length value or key that represents the original
string. The difference between hashing and encryption is in how the data is stored. With encrypted
text, the data can be decrypted with a key. With the hash function, after the data is entered and con-
verted using the hash function, the plaintext is gone. The hashed data is simply there for compari-
son. For example, when a user enters a password, the password is hashed and then compared to the
stored hashed value. If the user forgets the password, it is impossible to decrypt the stored value,
and the password must be reset.
The purpose of encryption and hashing is to guarantee confidentiality so that only authorized enti-
ties can read the message.

7.1.2 Cryptography
Authentication, integrity, and confidentiality are components of cryptography. Cryptography is
both the practice and the study of hiding information.
Cryptographic services are the foundation for many security implementations and are used to en-
sure the protection of data when that data might be exposed to untrusted parties. Understanding the
basic functions of cryptography and how encryption provides confidentiality and integrity is im-
portant in creating a successful security policy. It is also important to understand the issues that are
involved in managing the encryption key.
The history of cryptography starts in diplomatic circles thousands of years ago. Messengers from a
king™s court took encrypted messages to other courts. Occasionally, other courts not involved in
the communication attempted to steal any message sent to a kingdom that they considered an ad-
versary. Not long after, military commanders started using encryption to secure messages.
Various cipher methods, physical devices, and aids have been used to encrypt and decrypt text:

One of the earliest methods may have been the scytale of ancient Greece, a rod allegedly used

by the Spartans as an aid for a transposition cipher. The sender and receiver had identical rods
(scytale) on which to wrap a transposed messaged.
The Caesar cipher is a simple substitution cipher that was used by Julius Caesar on the

battlefield to quickly encrypt a message that could easily be decrypted by his commanders.
196 CCNA Security Course Booklet, Version 1.0

The method to encrypt could compare two scrolls of letters, moving one scroll over by a
single key number or by turning the inner dial of a cipher wheel by a single key number.
The Vigenere Cipher was invented by Frenchman Blaise de Vigenere in the 16th century using

a polyalphabetic system of encryption. Based on the Caesar cipher, it encrypted plaintext
using a multi-letter key.
Thomas Jefferson, the third president of the United States, invented an encryption system that

was believed to have been used when he served as secretary of state from 1790 to 1793.
Arthur Scherbius invented an electro-mechanical encoding device called the Enigma in 1918

that he had sold to Germany. It served as a template for the machines that all the major
participants in World War II used. It was estimated that if 1,000 cryptanalysts tested four keys
per minute, all day, every day, it would take 1.8 billion years to try them all. Germany knew
their ciphered messages could be intercepted by the allies, but never thought they could be
Also during World War II, Japan was deciphering every code the Americans came up with. A

more elaborate coding system was needed, and the answer came in the form of the Navajo
code talkers. Not only were there no words in the Navajo language for military terms, the
language was unwritten and less than 30 people outside of the Navajo reservations could
speak it, and not one of them was Japanese. By the end of the war, more than 400 Navajo
Indians were working as code talkers.

Each of these encryption methods use a specific algorithm, called a cipher, to encrypt and decrypt
messages. A cipher is a series of well-defined steps that can be followed as a procedure when en-
crypting and decrypting messages.
There are several methods of creating cipher text:




In transposition ciphers, no letters are replaced; they are simply rearranged. An example of this
type of cipher is taking the message FLANK EAST ATTACK AT DAWN and transposing it to
read NWAD TAKCATTA TSAE KNALF. In this example, the key is to reverse the letters.
Another example of a transposition cipher is known as the rail fence cipher. In this transposition,
the words are spelled out as if they were a rail fence, meaning some in front and some in back
across several parallel lines. For example, a rail fence cipher that uses a key of three specifies that
three lines are required when creating the encrypted code. To read the message, read diagonally up
and down, following the rail fence.
Modern encryption algorithms, such as the Data Encryption Standard (DES) and the Triple Data
Encryption Standard (3DES), still use transposition as part of the algorithm.
Substitution ciphers substitute one letter for another. In their simplest form, substitution ciphers re-
tain the letter frequency of the original message.
The Caesar cipher was a simple substitution cipher. Every day there was a different key to use for
adjusting the alphabet. For example, if the key for the day was 3, the letter A was moved three
spaces to the right, resulting in an encoded message that used the letter D in place of the letter A.
Chapter 7: Cryptographic Systems 197

The letter E would be the substitute for the letter B, and so on. If the key for the day was 8, A be-
comes I, B becomes J, and so on.
Because the entire message relied on the same single key shift, the Caesar cipher is referred to as a
monoalphabetic substitution cipher. It is also fairly easy to crack. For this reason, polyalphabetic
ciphers, such as the Vigenere cipher, were invented. The method was originally described by Gio-
van Battista Bellaso in 1553, but the scheme was later misattributed to the French diplomat and
cryptographer, Blaise de Vigenere.
The Vigenere cipher is based on the Caesar cipher, except that it encrypts text by using a different
polyalphabetic key shift for every plaintext letter. The different key shift is identified using a
shared key between sender and receiver. The plaintext message can be encrypted and decrypted
using the Vigenere Cipher Table.
To illustrate how the Vigenere Cipher Table works, suppose that a sender and receiver have a
shared secret key composed of these letters: SECRETKEY. The sender uses this secret key to en-
code the plaintext FLANK EAST ATTACK AT DAWN:

The F (FLANK) is encoded by looking at the intersection of column F and the row starting

with S (SECRETKEY), resulting in the cipher letter X.
The L (FLANK) is encoded by looking at the intersection of column L and the row starting

with E (SECRETKEY), resulting in the cipher letter P.
The A (FLANK) is encoded by looking at the intersection of column A and the row starting

with C (SECRETKEY), resulting in the cipher letter C.
The N (FLANK) is encoded by looking at the intersection of column N and the row starting


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