Cisco NX-OS/IOS Layer-3 Virtualization Comparison

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Objective

This tech note outlines the main differences in Layer 3 virtualization 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.


Virtualization Routing and Forwarding Overview

Virtual Routing and Forwarding (VRF) provides an additional layer of network virtualization on top of virtual device contexts (VDCs). VRF provides separate unicast and multicast address space and associated routing protocols that make independent forwarding decisions. All unicast and multicast protocols support VRF.


Important Cisco NX-OS and Cisco IOS Softfware Differences

In Cisco NX-OS:

  • Cisco NX-OS supports 8192 VRF instances per device.
  • Two VRF instances are configured by default. The management port on the supervisor module is assigned to the management VRF, and all I/O module ports are assigned to the default VRF.
  • The default VRF is the default routing context for all show commands.
  • VRF instances can be enabled without any command-line interface (CLI) prerequisites. Cisco IOS Software requires ip cef to be enabled globally before VRF instances can be configured.
  • The CLI for enabling VRF routing for a protocol is consistent for all routing protocols, whereas Cisco IOS Software uses address families for Border Gateway Protocol (BGP), Routing Information Protocol (RIP), and Enhanced Interior Gateway Routing Protocol (EIGRP) and requires unique routing process IDs per VRF for Integrated Intermediate System-to-Intermediate System (ISIS) and Open Shortest Path First (OSPF).
  • In Cisco NX-OS, numerous VRF instances can be assigned to a single routing protocol instance.
  • IP static routes are configured under the specified vrf context. In Cisco IOS Software, all static routes are configured in global configuration mode with the vrf option.
  • A VRF instance can be manually disabled with the shutdown command. Cisco IOS Software does not have the CLI capability to manually disable a VRF instance.


Things You Should Know

The following list provides some additional facts about Cisco NX-OS that should be helpful when configuring and maintaining VRF instances.


  • When you assign a VRF instance to an interface with an IP address previously configured, the interface IP address is automatically removed.
  • Static routes or dynamic routing protocols can be configured for routing in a VRF instance (BGP, EIGRP, ISIS, OSPF, static routes, and RIPv2).
  • IP troubleshooting tools such as ping and traceroute are VRF aware and require the name of a specific VRF instance if testing in the default VRF instance is not desired.
  • Network management–related services such as authentication, authorization and accounting (AAA), Call Home, Domain Name System (DNS), FTP, HTTP, NetFlow Network Time Protocol (NTP), RADIUS, Simple Network Management Protocol (SNMP), SSH, syslog, TACACS+, Telnet, Trivial File Transfer Protocol (TFTP), and XML are VRF aware.


Configuration Comparison

The following sample code shows configuration similarities and differences between the Cisco NX-OS and Cisco IOS Software CLIs. Sample code is provided only to illustrate how to enable VRF routing. The Cisco NX-OS CLI is simpler and more consistent since it allows multiple VRF instances to be assigned to a single routing protocol instance, whereas Cisco IOS Software uses different techniques depending on the routing protocol.


Cisco IOS CLI Cisco NX-OS CLI
Creating a VRF
ip cef

ip vrf vrf-1

vrf context vrf-1
Assigning an Interface to a VRF
interface Ethernet2/1

ip vrf forwarding vrf-1

ip address 192.168.10.1 255.255.255.0

interface Ethernet2/1

vrf member vrf-1

ip address 192.168.10.1/24

Enabling BGP in a VRF
router bgp 10


address-family ipv4 vrf vrf-1

neighbor 192.168.10.2 remote-as 20

neighbor 192.168.10.2 activate

network 192.168.1.1 mask 255.255.255.255

exit-address-family

router bgp 10

vrf vrf-1

address-family ipv4 unicast

network 192.168.1.1/32

neighbor 192.168.10.2 remote-as 20

address-family ipv4 unicast

Enabling EIGRP in a VRF
router eigrp 10


address-family ipv4 vrf vrf-1

network 192.168.10.0

auto-summary

autonomous-system 10

exit-address-family!

interface Ethernet2/1

vrf member vrf-1

ip address 192.168.10.1/24

ip router eigrp 10


router eigrp 10

vrf vrf-1

Enabling ISIS in a VRF
interface Ethernet2/1

ip vrf forwarding vrf-1

ip address 192.168.10.1 255.255.255.0

ip router isis 10


router isis 10

vrf vrf-1

net 49.0001.0000.0001.00

interface Ethernet2/1

vrf member vrf-1

ip address 192.168.10.1/24

ip router isis 10


router isis 10

vrf vrf-1

net 49.0001.0000.0001.00

Enabling OSPF in a VRF
interface Ethernet2/1

ip vrf forwarding vrf-1

ip address 192.168.10.1 255.255.255.0


router ospf 10 vrf vrf-1

network 192.168.10.0 0.0.0.255 area 0

interface Ethernet2/1

vrf member vrf-1

ip address 192.168.10.1/24


ip router ospf 10

router ospf 10

vrf vrf-1

Enabling RIPv2 in a VRF
interface Ethernet2/1

ip vrf forwarding vrf-1

ip address 192.168.10.1 255.255.255.0


router rip

address-family ipv4 vrf vrf-1

network 192.168.10.0

version 2

exit-address-family

interface Ethernet2/1

vrf member vrf-1

ip address 192.168.10.1/24

ip router rip 10


router rip 10

vrf vrf-1

Configuring Static Routes in a VRF
ip route vrf vrf-1 192.168.2.0 255.255.255.0 192.168.10.2 vrf context vrf-1

ip route 192.168.2.0/24 192.168.10.2



Verification Command Comparison

The following table compares some useful show commands for verifying and troubleshooting VRF instances.


Cisco NX-OS VRF Cisco IOS Software VRF Command Description
show vrf show ip vrf Displays a list of all configured VRF instances
show vrf <name> show ip vrf <name> Displays a specific VRF instance
show vrf <name> detail show ip vrf detail <name> Displays details for a specific VRF instance
show vrf <name> interface - Displays the interface assignment for a specific VRF instance
show vrf default - Displays a summary of the default VRF instance
show vrf detail show ip vrf detail Displays details for all VRF instances
show vrf interface show ip vrf interface Displays VRF interface assignments
show vrf management - Displays a summary of the management VRF instance
- - -
show ip route vrf all - Displays routes for all VRF instances
show ip route vrf default - Displays routes for the default VRF instance
show ip route vrf management - Displays routes for the management VRF instance
show ip route vrf <name> show ip route vrf <name> Displays routes for a specific VRF instance
- - -
show ip arp vrf <name> show ip arp vrf <name> Displays Address Resolution Protocol (ARP) entries for a specific VRF instance
- - -
show ip bgp vrf <name> show ip bgp vpnv4 vrf <name> Displays BGP commands for a specific VRF instance
show ip eigrp vrf <name> show ip eigrp vrf <name> Displays EIGRP information for specific VRF instance
show ip isis vrf <name> show isis <#> Displays ISIS commands for a specific VRF instance
show ip ospf vrf <name> show ip ospf <#> Displays OSPF information for a specific VRF instance
show ip rip vrf <name> show ip rip database vrf <name> Displays RIP information for a specific VRF instance
show ip static-route vrf <name> - Displays static routes for a specific VRF instance

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