• To activate ORF, we need exchange ORF capability between BGP peers.
• BGP - ORF feature does not support multicast.
• For the ORF feature. We should use only the prefix-list( distribute-list or access-list are not supported).
• To use the ORF feature, we need to have "address-family" configure.
• ORF only works with e-BGP.

Lab time!

In our topology, we have two routers. one is our router in BGP AS 1 which attached to ISP in BGP AS 2.

Let check out the configuration on our router and verify the BGP relationship:

Here we can verify the BGP relationship:

Now are going to show how many routes our isp has, At this lab, I used six loopbacks with a different subnet mask.

Now I will redistribute the loopbacks to BGP routing table, as a result, as you can see in the picture, we have many routs coming from ISP.

Let's activate ORF 

Step 1:

Create a filter-list to filter our determined subnet.

Imagine we want to filter any 10.10.10.0 subnet start from /28 to /32

 

#ip prefix-list deny-isp seq 10 deny 10.10.10.0/28 le 32

#ip prefix-list deny-isp seq 20 permit 10.10.10.0/0 le 27

 

Step 2:

Configure for ISP neighbor inbound prefix-list on r1 (our router) 

Step 3:

Configure capability of ORF! use send on r1 and configure ORf capability with receive option to ISP router

Step 4:

Verification

In this picture, we can see the routing table! exactly as we expected:

and to check orf capability on R1 and also ISP router check this output

On r1 use this command

# sh ip bgp neighbors ----check the output of address-family

and on ISP use this command to verification:

 #show ip bgp neighbors 1.1.1.1 received prefix-filter