Eigrp Named Mode

You’re feeling pretty confident in your understanding of Cisco’s Enhanced Interior Gateway Routing Protocol (EIGRP), but then somebody mentions something called EIGRP named mode configuration, or possibly even Named EIGRP, and suddenly you’re all like …..?!?

CCNP candidate is required to have at least a passing knowledge of EIGRP named mode and how it differs from classic EIGRP.

Classic EIGRP, which is also referred to as EIGRP Autonomous System (AS) mode, is how most people think of EIGRP. A simple classic EIGRP configuration begins with he ever-familiar router eigrp autonomous-system command, where autonomous-system is a value between 1 and 65535. You can use the context-sensitive help functionality in IOS to confirm the command syntax as shown below:

R12.4(config)#router eigrp ?
  <1-65535>  Autonomous system number

The output in the previous example is from a router running IOS 12.4. As you can see, this particular version of IOS supports EIGRP configuration only by using EIGRP AS mode. By contrast, the context-sensitive help on a router that supports Named EIGRP configuration provides slightly different output, as shown below:

R15.2(config)#router eigrp ?
  <1-65535>  Autonomous System
  WORD       EIGRP Virtual-Instance Name

The output above is from a router running IOS 15.2. As you can see, this particular IOS version has an additional parameter available for the router eigrp command. The virtual-instance-name parameter lets you identify an EIGRP process by its virtual instance name instead of its AS number. When you refer to the EIGRP process by name, you tell the router to enter Named EIGRP configuration mode. It is important to note that the virtual instance name is case sensitive.

Whether a router supports named mode depends on the version of IOS that is running on the router. Even if the IOS version shows support for Named EIGRP, the implementation may be incomplete or may function only in an experimental capacity. It is generally a good idea to avoid using Named EIGRP unless you’re running a very recent IOS revision with solid Named EIGRP implementation, such as version 15.2 or later.

Let’s continue our classic EIGRP example. Typically, after entering router configuration mode, the first thing you want to do is make sure that the EIGRP automatic summarization behavior is set to whatever you expect it to be. Cisco has been pretty inconsistent with the default behavior of this feature on various platforms over the years. Additionally, it is best practice to manually configure a setting so that the default behavior does not surprise you later. The no auto-summary command disables the automatic route summarization feature, which is typically the desired behavior. Next, use the network ip-address [wildcard-mask] command to specify one or more router interfaces that the EIGRP routing process should use to advertise and receive routing updates. For example, the following commands would disable automatic route summarization and enable EIGRP on an interface with the IP address 1.1.1.1 and the network mask of 255.255.255.0:

R12.4(config-router)#no auto-summary
R12.4(config-router)#network 1.1.1.1 0.0.0.255

You can use the context-sensitive help feature to see additional commands that are available in EIGRP router configuration mode:

R12.4(config-router)#?
Router configuration commands:
  address-family       Enter Address Family command mode
  auto-summary         Enable automatic network number summarization
  bfd                  BFD configuration commands
  default              Set a command to its defaults
  default-information  Control distribution of default information
  default-metric       Set metric of redistributed routes
  distance             Define an administrative distance
  distribute-list      Filter networks in routing updates
  eigrp                EIGRP specific commands
  exit                 Exit from routing protocol configuration mode
  help                 Description of the interactive help system
  maximum-paths        Forward packets over multiple paths
  metric               Modify EIGRP routing metrics and parameters
  neighbor             Specify a neighbor router
  network              Enable routing on an IP network
  no                   Negate a command or set its defaults
  offset-list          Add or subtract offset from RIP metrics
  passive-interface    Suppress routing updates on an interface
  redistribute         Redistribute information from another routing protocol
  timers               Adjust routing timers
  traffic-share        How to compute traffic share over alternate paths
  variance             Control load balancing variance

As you can see, the EIGRP routing process offers quite a few configurable options. However, what if you wanted to adjust the Hello or hold timer intervals, or enable MD5 authentication? There is no commands in router configuration mode that let you achieve those tasks. Of course, if you’re familiar with classic EIGRP configurations, you well know that those options are all available in interface configuration mode. Thus you’ll need to leave router configuration mode and enter interface configuration mode to make those changes. Additionally, none of the interface configuration mode changes will be stored in the EIGRP section of the running configuration; instead, they’ll all be bunched up under the appropriate interface to which each respective command refers. This scattered configuration can make it difficult to view all of the EIGRP configuration parameters in the appropriate context, and that can quickly lead to configuration errors.

Now let’s talk about Named mode..

Named EIGRP is Cisco’s attempt to improve the way you configure EIGRP. With Named EIGRP, all of the EIGRP routing process parameters reside in a single, hierarchical section of the running configuration. No longer are EIGRP commands scattered throughout the running configuration. Named EIGRP also provides consistency between the IPv4 and IPv6 EIGRP commands and their parameters. Let’s take a look at a simple Named And classic mode EIGRP configuration:

Named Mode Eigrp Configuration->

router eigrp GNK
 !
 address-family ipv4 unicast autonomous-system 100
  !
  af-interface FastEthernet0/1
   passive-interface
  exit-af-interface
  !
  topology base
   No auto-summary
  exit-af-topology
  network 192.168.14.0 0.0.0.3
  network 192.168.14.4 0.0.0.3

 exit-address-family

Classic Mode Eigrp Configuration --->

router eigrp 10
 passive-interface FastEthernet0/1
  network 192.168.14.0 0.0.0.3
  network 192.168.14.4 0.0.0.3
  no auto-summary

  exit

The first thing you might notice in the output above is that the EIGRP process is assigned a name,GNK in this case. As you will see, Named EIGRP enables you to configure both an IPv4 address family and an IPv6 address family under the same process (using different AS numbers, of course). In our example, an IPv4 address family is defined and associated with AS number 100. Within that address family are contained all of the parameters which affect the operation of the EIGRP for IPv4 process. In our example, we have Disabled automatic route summarization, declared interface Fa0/1 as a passive interface, and enabled EIGRP on interfaces in the 192.168.14.0/30 and 192.168.14.4/30 network range.

At this point, you might be thinking “The classic EIGRP configuration is so much easier , why would I use Named EIGRP at all?” The answer becomes more evident when we add additional configuration parameters. Let’s take authentication for example. The following output shows the Named EIGRP configuration modified to enable MD5 authentication on interface Fa0/2:

router eigrp GNK
 !
 address-family ipv4 unicast autonomous-system 100
  !
  af-interface FastEthernet0/1
   passive-interface
  exit-af-interface
  !
  af-interface FastEthernet0/2
   authentication mode md5
   authentication key-chain ANYKEY
  exit-af-interface
  !
  topology base
   NO auto-summary
  exit-af-topology
  network 192.168.14.0 0.0.0.3
  network 192.168.14.4 0.0.0.3
 exit-address-family

The equivalent classic EIGRP configuration would have the authentication commands clustered in the interface section of the running configuration, as shown in the following example:

!<LOTS OF OTHER CONFIG STUFF>
interface FastEthernet0/2
 ip address 192.168.14.1 255.255.255.252
 ip authentication mode eigrp 100 md5
 ip authentication key-chain eigrp 100 ANYKEY
!
!<LOTS OF OTHER CONFIG STUFF>
!
router eigrp 100
 passive-interface FastEthernet0/1

  network 192.168.14.0 0.0.0.3
  network 192.168.14.4 0.0.0.3
  No Auto-Summary

I’ve done you the favor of snipping out the bits of the running configuration between the relevant interface section and the EIGRP section. You might notice that not only is the classic EIGRP authentication code clustered in a different section from the rest of the EIGRP configuration, the classic mode commands also contain potential mistake-enabling complexity. For example, the inclusion of the AS in the authentication commands is necessary for the router to tie the commands back to the appropriate routing process, but they can also be easily overlooked or misread when parsed by a human. As an EIGRP configuration grows more complex, the hierarchical structure of a Named EIGRP configuration makes the overall configuration easier to grok, even if it might seem more convoluted at first glance when using a simple configuration as an example.

Now that you’ve had a rough comparison between a Named EIGRP configuration and a classic EIGRP configuration, let’s take a look at the basics of EIGRP named configuration mode. As you saw in a previous example, you can issue the router eigrp virtual-name command to enter EIGRP named configuration mode, where virtual-name is the name you want to assign to the routing process. On routers that support EIGRP named mode configurations, you will see the following output when using context-sensitive help:

R15.2(config)#router eigrp ?
  <1-65535>  Autonomous System
  WORD       EIGRP Virtual-Instance Name

Once you have entered EIGRP named configuration mode, you’ll see that the number of options you have available seem significantly fewer than those available in a classic EIGRP configuration. Context-sensitive help shows the following options:

R15.2(config-router)#?
Router configuration commands:
  address-family  Enter Address Family command mode
  default         Set a command to its defaults
  exit            Exit from routing protocol configuration mode
  no              Negate a command or set its defaults
  service-family  Enter Service Family command mode
  shutdown        Shutdown this instance of EIGRP

Because EIGRP named mode uses a hierarchical command structure, the majority of commands that you might be accustomed to using in an EIGRP configuration are grouped into three main sections: address family configuration mode, address family interface configuration mode, and address family topology configuration mode. Let’s start with address family configuration mode.

You can issue the address-family command to enter address family configuration mode. The syntax for the address-family command is address-family { ipv4 | ipv6 } [multicast | unicast] [ vrf vrf-name ]autonomous-system autonomous-system-number.  Once you’ve entered address family configuration mode, you’ll see a few more of the EIGRP parameters you might have been expecting in EIGRP router configuration mode:

R15.2(config-router-af)#?
Address Family configuration commands:
  af-interface         Enter Address Family interface configuration
  default              Set a command to its defaults
  eigrp                EIGRP Address Family specific commands
  exit-address-family  Exit Address Family configuration mode
  help                 Description of the interactive help system
  maximum-prefix       Maximum number of prefixes acceptable in aggregate
  metric               Modify metrics and parameters for address advertisement
  neighbor             Specify an IPv4 neighbor router
  network              Enable routing on an IP network
  no                   Negate a command or set its defaults
  shutdown             Shutdown address family
  timers               Adjust peering based timers
  topology             Topology configuration mode

The sample router output above is from the IPv4 address family we used as an example earlier in this post. The commands would be almost identical for an IPv6 address family, with the exception of the network command. In an IPv6 address family, EIGRP is enabled automatically for every IPv6 enabled interface. Therefore, the network command is not necessary (although the passive-interface command may suddenly have significantly greater importance =-).

From within address family configuration mode, you can issue the af-interface { default | interface-type interface-number } command to access address family interface configuration mode. This mode enables you to configure interface specific EIGRP parameters, such as route summarization, split-horizon, or a passive interface. The following output shows the available commands in address family interface configuration mode:

R15.2(config-router-af-interface)#?
Address Family Interfaces configuration commands:
  authentication      authentication subcommands
  bandwidth-percent   Set percentage of bandwidth percentage limit
  bfd                 Enable Bidirectional Forwarding Detection
  dampening-change    Percent interface metric must change to cause update
  dampening-interval  Time in seconds to check interface metrics
  default             Set a command to its defaults
  exit-af-interface   Exit from Address Family Interface configuration mode
  hello-interval      Configures hello interval
  hold-time           Configures hold time
  next-hop-self       Configures EIGRP next-hop-self
  no                  Negate a command or set its defaults
  passive-interface   Suppress address updates on an interface
  shutdown            Disable Address-Family on interface
  split-horizon       Perform split horizon
  summary-address     Perform address summarization

Likewise, you can issue the topology { base | topology-name tid number } command from within address family configuration mode to access address family topology configuration mode. This mode enables you to configure topology specific EIGRP parameters such as redistribution, default information origination, load balancing, and metric (K-value) values.  The following output shows the available commands in address family topology configuration mode:

R15.2(config-router-af-topology)#?
Address Family Topology configuration commands:
  auto-summary         Enable automatic network number summarization
  default              Set a command to its defaults
  default-information  Control distribution of default information
  default-metric       Set metric of redistributed routes
  distance             Define an administrative distance
  distribute-list      Filter entries in eigrp updates
  eigrp                EIGRP specific commands
  exit-af-topology     Exit from Address Family Topology configuration mode
  fast-reroute         Configure Fast-Reroute
  maximum-paths        Forward packets over multiple paths
  metric               Modify metrics and parameters for advertisement
  no                   Negate a command or set its defaults
  offset-list          Add or subtract offset from EIGRP metrics
  redistribute         Redistribute IPv4 routes from another routing protocol
  snmp                 Modify snmp parameters
  summary-metric       Specify summary to apply metric/filtering
  timers               Adjust topology specific timers
  traffic-share        How to compute traffic share over alternate paths
  variance             Control load balancing variance

With these three modes , you should be able to configure an EIGRP named mode implementation just as smoothly as you might have once implemented a classic EIGRP configuration. In fact, you might find it even easier to configure than a classic configuration

To make things even easier, Cisco provides a utility, the eigrp upgrade-cli command, which automagically converts classic EIGRP configurations into Named EIGRP configurations with a single command and without an interruption in service. Naturally, this convenient command is not available on all versions of IOS, much like Named EIGRP itself is not available on all versions of IOS[only with ISO Version 15.4 or Higher].