Cisco Catalyst - On core ip vrf forwarding

[TCCS TCS]

Hello Experts,

On our Core switch I see below commands in show run configuration. This Core which has  agg1 and agg2 connected.

interface Vlan345

ip vrf forwarding TEST

 ip address 10.99.1.49 255.255.255.252

interface Vlan346
 

ip vrf forwarding TEST

 ip address 10.99.1.50 255.255.255.252

Can you help me understand use of this command? The core on the external side goes to internet via 3750 and then goes to ISP switches.

[konstantinoschiotakis]

Hello,

Just a brief explanation of the VRF:

Virtual Routing and Forwarding (VRF) is an IP technology that allows multiple instances of a routing table to coexist on the same router at the same time. Because the routing instances are independent, the same or overlapping IP addresses can be used without conflict. "VRF" is also used to refer to a routing table instance that can exist in one or multiple instances per each VPN on a Provider Edge (PE) router.

You can find more here: 

http://www.cisco.com/c/en/us/td/docs/net_mgmt/active_network_abstraction/3-7/reference/guide/ANARefGuide37/vrf.html

Basically the commands will put the SVIs 345 and 346 under the VRF TEST. So if you type "show ip vrf br" you will get a list of all the VRFs and the VLANs associated with them. The VLANs under the same VRF will be allowed to talk to each other but communication to the other VRFs is restricted by default (you will have to manually allow the communication).

Hope this helps.

[Julio E. Moisa]

Hi

Please correct me if Im wrong but you want to know about the vrf forwarding command, right?

Well VRF is used to create a separate routing table from the global routing table and their routing processes on a same device.

In order to enable the communication between other devices you have to configure the command ip vrf forwarding <VRF Name> under the interface facing your other devices. But caution it will remove your ip address under that interface, so you must type it again under the interface. 

If you create the vrf TEST you will have 2 routing tables on your devices...... 1 global routing table (you can see that using show ip route) and the routing table associated to vrf TEST (show ip route vrf TEST). They cannot see each other unless you make special configurations.

Regards.