BGP Filtering

• BGP filtering can be done on any routers
• Filtering can be done inbound and outbound
• After filtering is applied BGP neighbor must be reset or cleared for the filter to take effect
  • clear ip bgp 20.20.20.20 in/out  preferred
  • clear ip bgp *   (hard reset)
  • clear ip bgp 20.20.20.20 soft in/out

How to filter:

Distribute lists

access-list 1 deny 30.30.30.0 0.0.0.255
access-list 1 permit any any
R2#(config)router bgp 20
R2#(config-router)neighbour 20.20.20.20 distribute-list 1 in

Prefix-lists

ip prefix-list CCNP deny 30.30.30.0/24 le 32
ip prefix-list CCNP permit 0.0.0.0/0 le 32
R2#(config)router bgp 20
R2#(config-router)neighbour 20.20.20.20 prefix-list CCNP in

Filter-lists

ip as-path access-list 1 permit ^10_
ip as-path access-list 1 permit _10$
R2#(config)router bgp 20 
R2#(config-router)neighbour 20.20.20.20 filter-list 1 in

Route-map