Cisco NX-OS/IOS EIGRP Comparison

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Objective

This tech note outlines the main differences in Enhanced Interior Gateway Protocol (EIGRP) support between Cisco® NX-OS Software and Cisco IOS® Software. Sample configurations are included for Cisco NX-OS and Cisco IOS Software for some common features to demonstrate the similarities and differences. Please refer to the NX-OS documentation on Cisco.com for a complete list of supported features.

EIGRP Overview

EIGRP is a Cisco proprietary hybrid distance vector routing protocol used to exchange network reachability information within an autonomous system.

Important Cisco NX-OS and Cisco IOS Software Differences

In Cisco NX-OS:

• EIGRP command-line interface (CLI) configuration and verification commands are not available until you enable the EIGRP feature with the feature eigrp command.
• The EIGRP protocol requires the Enterprise Services license.
• The EIGRP instance can consist of 20 characters. Cisco IOS Software supports numbers 1- 65536.
• Eight equal-cost paths are supported by default; Cisco NX-OS supports up to 16.
• Route auto-summarization is disabled by default.
• Networks and interfaces are added to an EIGRP instance under the interface configuration mode.
• If a router ID is not manually configured, the loopback 0 IP address is always preferred. If loopback 0 does not exist, Cisco NX-OS selects the IP address for the first loopback interface in the configuration. If no loopback interfaces exist, Cisco NX-OS selects the IP address for the first physical interface in the configuration.
• A default route can be generated with the default-information originate command, whereas Cisco IOS Software requires additional CLI commands to achieve similar results.
• When interface authentication is configured, the EIGRP key is encrypted with Data Encryption Standard 3 (3DES) in the configuration. Cisco IOS Software requires the service password command.
• Distribute-lists used to filter routes from routing updates are applied under the interface with the ip distribute-list eigrp command, as opposed to under the EIGRP router instance.
• Maximum prefix thresholds (warning and withdraw) can be configured for redistributed routes using the redistribute maximum-prefix routing process command. Cisco IOS Software does not have the ability to set maximum prefix thresholds for redistributed routes.

Things You Should Know

The following list provides some additional facts about Cisco NX-OS that should be helpful when designing, configuring, and maintaining an EIGRP network.

• Four EIGRP instances can be configured per virtual device context (VDC).
• Numerous Virtual Route Forwarding (VRF) instances can be associated with an EIGRP instance.
• If the feature eigrp command is removed, all relevant EIGRP configuration information is also removed.
• The shutdown command can be used to gracefully disable an EIGRP instance while retaining the configuration. This feature can also be applied per interface with the ip eigrp <instance> shutdown command.
• The show running-config eigrp command displays the current EIGRP configuration.
• An EIGRP instance can be restarted with the restart eigrp <instance> command.
• Graceful restart (RFC 3623) is enabled by default (It needs to be enabled in order to perform an ISSU upgrade.)
• Multiple EIGRP instances can be configured on the same interface.
• Secondary IP addresses are advertised by default and cannot be suppressed per interface.
• EIGRP supports Bidirectional Forwarding Detection (BFD) to reduce network convergence time to less than one second.

Configuration Comparison

The following sample code shows configuration similarities and differences between the Cisco NX-OS and Cisco IOS Software CLIs. There are three significant differences: Cisco NX-OS allows EIGRP to be enabled and disabled globally, and it has a more interface-centric configuration that makes it easier to read. In addition, Cisco NX-OS has the capability to generate a default route, whereas Cisco IOS Software requires additional CLI commands to achieve similar results.

Cisco IOS CLI	Cisco NX-OS CLI
Enabling the EIGRP Feature

Cisco IOS Software does not have the ability to enable or disable EIGRP.	feature eigrp

Configuring an EIGRP Instance and Router ID

router eigrp 10 eigrp router-id 192.168.1.1	router eigrp 10 router-id 192.168.1.1

Associating a Network with an EIGRP Instance

router eigrp 10 network 192.168.10.0	interface Ethernet2/1 ip address 192.168.10.1/24 ip router eigrp 10

Configuring a Passive Interface

router eigrp 10 network 192.168.10.0 passive-interface GigabitEthernet2/1	interface Ethernet2/1 ip address 192.168.10.1/24 ip router eigrp 10 ip passive-interface eigrp 10

Configuring Interface Authentication (MD5)

key chain eigrp-key key 1 key-string cisco123 interface GigabitEthernet2/1 ip address 192.168.10.1 255.255.255.0 ip authentication mode eigrp 10 md5 ip authentication key-chain eigrp 10 eigrp-key	key chain eigrp-key key 1 key-string 7 070c285f4d06485744 interface Ethernet2/1 ip address 192.168.10.1/24 ip router eigrp 10 ip authentication mode eigrp 10 md5 ip authentication key-chain eigrp 10 eigrp-key

Configuring an EIGRP Distribution List to Filter Routes

ip prefix-list eigrp-10-list seq 5 permit 159.142.1.0/24 router eigrp 10 network 192.168.10.0 distribute-list prefix eigrp-10-list out GigabitEthernet2/1	ip prefix-list eigrp-10-list seq 5 permit 159.142.1.0/24 interface Ethernet2/1 ip address 192.168.10.1/24 ip router eigrp 10 ip distribute-list eigrp 10 prefix-list eigrp-10-list out

Configuring Route Summarization

interface GigabitEthernet2/1 ip address 192.168.10.1 255.255.255.0 ip summary-address eigrp 10 159.142.0.0 255.255.0.0 5	interface Ethernet2/1 ip address 192.168.10.1/24 ip router eigrp 10 ip summary-address eigrp 10 159.142.0.0/16

Generating A Default Route (Conditional)

Cisco IOS Software doesn’t have the same CLI to generate a default route, but redistribution or the ip summary address command can be used to achieve similar results.	router eigrp 10 default-information originate

Verification Command Comparison

The following table compares some useful show commands for verifying and troubleshooting an EIGRP network configuration.

Cisco NX-OS EIGRP	Cisco IOS Software EIGRP	Command Description
show ip eigrp	show ip eigrp <#>	Displays all EIGRP information for a specified process
show ip eigrp accounting	-	Displays the number of prefixes that each neighbor advertised
show ip eigrp interfaces	show ip eigrp interfaces	Displays interfaces configured for EIGRP
show ip eigrp interfaces detail	show ip eigrp interfaces detail	Displays detailed interface information
show ip eigrp neighbors	show ip eigrp neighbors	Displays currently connected neighbors
show ip eigrp neighbors detail	show ip eigrp neighbors detail	Displays connected neighbors and associated details
show ip eigrp route	-	Displays EIGRP routes
show ip eigrp route-map statistics redistribute <protocol>	-	Displays statistics for redistributed routes per protocol
show ip eigrp topology	show ip eigrp topology	Displays the EIGRP topology table
show ip eigrp traffic	show ip eigrp traffic	Displays statistics related to EIGRP
show ip eigrp vrf	-	Displays VRF information for a specified VRF instance