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Backup link Reduncy in BGP

Current Set up


  • Primary router R1 is connected to MPLS cloud
  • Backup router R2 is connected to MPLS cloud
  • Both primary and backup link have same bandwidth
  • For incoming traffic primary link in R1 is preferred because of best AS-Path
  • Backup link in R2 has as-prepend configured in R2, so it is considered as backup
  • For outgoing, R1 is preferred because of higher local preference configured in R1
  • R2 is preferred as backup because of lower local preference configured in R2
  • R1 is connected to switch S1
  • R2 is connected to switch S2
  • Switch S1 and S2 are interconnected and all the LAN switches connect to S1 or S2

Now, Switch S1 is down and site isolated, because incoming traffic is via R1 and then it goes to S1 which is down and packet dropped. Outgoing is via switch S2 and then to R2.

Could you please confirm how we can manipulate with BGP attribute or any other method to avoid site isolation incase of switch S1 is down and R1 should advertise as worst router or do not advertise so that R2 will be preferred for incoming traffic.

Many thanks in advance for your reply.


Backup link Reduncy in BGP

Hi Shakir,

You have good setup...

Only thing you need to run on router is HSRP or VRRP; which will protect you from any single point of failure of switches...



New Member

Backup link Reduncy in BGP

Your setup is good but very basic in my opinion. You could implement some IOS features to improve redundancy under specific scenarios.

In case you have another Fast/GigaEthernet, you could use them to bound with the already existent interface to make a BVI interfaces. This is a feature that allows you to bring the benefits of spanning-tree to your router. a BVI interface is a virtual interface with two phisycal interfaces bounded to it, so you can connect R1 to S1 and S2. The same goes to R2.

Don't worry, one of the phisycal interfaces will be in blocked state depending on your configuration (root bridge, port priority, etc).

Also, you can implement HSRP (but in this case, the HSRP, and all interface IP configuration will be made on the BVI interfaces) and use a track option to put the active router in standby mode when the line protocol of the WAN connection goes down. Or you can go farther, doing some tricks with Event manager to make the HSRP change when the BGP session goes down.