AR359

[pc_evans]

Only Allow Networks that Originate from AS 4 to Enter Router 1


Placing 'ip as-path access-list 1 permit ^111$ on ISP-1 only allows ISP-1 to receive routers from AS111.  


See example from 
https://www.cisco.com/c/en/us/support/do...1227473857


If you would like for Router 1 to receive only the routes originated from AS 4 (and no Internet routes), you can apply an inbound access list on Router 1:

ip as-path access-list 1 permit ^4$
router bgp 1
neighbor 10.4.4.4 remote-as 4
neighbor 10.4.4.4 route-map foo in
route-map foo permit 10
match as-path 1

This ensures only networks originated from AS 4 are allowed into Router 1.