Hello,
this is possible for sure. Do you have your own official AS number? If not, then the config gets somewhat more tricky.
In case you have an official AS number the config could look like this:
interface Ethernet0/1
description to ISP1
ip address 1.4.x.x.x.255.252
interface Ethernet0/2
description to ISP2
ip address 2.2.x.x.x.255.252
router bgp 65000
network 1.1.0.0 mask 255.255.0.0
neighbor 1.4.5.1 remote-as 1 ! ISP1
neighbor 1.4.5.1 prefix-list NoTrash in
neighbor 1.4.5.1 filter-list 1 out
neighbor 1.4.5.1 weight 150
neighbor 2.2.2.1 remote-as 2 ! ISP2
neighbor 2.2.2.1 prefix-list NoTrash in
neighbor 2.2.2.1 filter-list 1 out
neighbor 2.2.2.1 weight 100
no auto-summary
ip as-path access-list 1 permit ^$
ip prefix-list NoTrash deny 192.168.0.0/16 le 32
ip prefix-list NoTrash deny 172.16.0.0/12 le 32
ip prefix-list NoTrash deny 10.0.0.0/8 le 32
ip prefix-list NoTrash deny 1.1.0.0/16 le 32
ip prefix-list NoTrash permit 0.0.0.0/0 le 32
ip route 1.1.x.x.255.0.0 Null 0 250
This would not announce only the assigned IP addresses (assumed 1.1.0.0/16) to ISP1 and ISP2, i.e. it prevents that you become transit AS between them. Also all RFC1918 routes are blocked. You could extend this and use the BOGON list for filtering, but this would require more maintainance, because you have to adjust the filters from time to time. For a customer it should be sufficient to block all routes you potentially have internally.
You need to adjust IP addresses, AS numbers and prefix to your environment.
In this example ISP1 is primary and ISP2 is backup (selected through weight). In case you want to have a more flexible selection you should use an incoming route-map to set f.e. Local Preference.
Hope this helps! Please rate all posts.
Regards, Martin
