SOURCECODEBD.NET

Live Experience

Two Link to The Same ISP with Backup

TWO LINK TO THE SAME ISP WITH BACKUP
 
Two links to the same ISP
One link primary, the other link backup only
 
• AS109 removes private AS and any customer subprefixes from Internet announcement
 
• Announce /19 aggregate on each link primary link makes standard announcement
  backup link increases metric on outbound, and reduces local-pref on inbound
 
• When one link fails, the announcement of the /19 aggregate via the other link
   ensures continued connectivity
 
 
• RouterA Configuration 
 
router bgp 200 
    network 221.10.0.0 mask 255.255.224.0 
    neighbor 222.222.10.2 remote-as 109 
    neighbor 222.222.10.2 description RouterC 
    neighbor 222.222.10.2 prefix-list aggregate out 
    neighbor 222.222.10.2 prefix-list default in 
 
ip prefix-list aggregate permit 221.10.0.0/19 
ip prefix-list default permit 0.0.0.0/0 
 
 
 
• RouterB Configuration 
 
router bgp 200 
   network 221.10.0.0 mask 255.255.224.0 
   neighbor 222.222.10.6 remote-as 109 
   neighbor 222.222.10.6 description RouterD 
   neighbor 222.222.10.6 prefix-list aggregate out 
   neighbor 222.222.10.6 route-map routerD-out out 
   neighbor 222.222.10.6 prefix-list default in 
   neighbor 222.222.10.6 route-map routerD-in in 
 
!
ip prefix-list aggregate permit 221.10.0.0/19 
ip prefix-list default permit 0.0.0.0/0 
 
route-map routerD-out permit 10 
    match ip address prefix-list aggregate 
    set metric 10 
route-map routerD-out permit 20 
 
route-map routerD-in permit 10 
     set local-preference 90 
!  
 
 
• RouterC Configuration (main link) 
 
router bgp 300 
    neighbor 222.222.10.1 remote-as 65534 
    neighbor 222.222.10.1 default-originate 
    neighbor 222.222.10.1 prefix-list Customer in 
    neighbor 222.222.10.1 prefix-list default out 
 
ip prefix-list Customer permit 221.10.0.0/19 
ip prefix-list default permit 0.0.0.0/0 
 
 
• RouterD Configuration (backup link) 
 
router bgp 300 
    neighbor 222.222.10.5 remote-as 65534 
    neighbor 222.222.10.5 default-originate 
    neighbor 222.222.10.5 prefix-list Customer in 
    neighbor 222.222.10.5 prefix-list default out 
 
 
ip prefix-list Customer permit 221.10.0.0/19 
ip prefix-list default permit 0.0.0.0/0 
 
 
• RouterE Configuration 
 
router bgp 300 
    neighbor 222.222.10.17 remote-as 110 
    neighbor 222.222.10.17 remove-private-AS 
    neighbor 222.222.10.17 prefix-list Customer out 
 
 
ip prefix-list Customer permit 221.10.0.0/19
You are here: Home / BGP / TWO LINK TO THE SAME ISP WITH BACKUP