BGP routing

[zulqurnain]

Hi Experts

I have a scenario in which I am kind of stuck and wondering if anyone can give me the best advice on how to accomplish it

Basically I have following scenario and what I am trying to achieve is create a high availability in case one physical connection goes down. 

Site 'A' and 'B' connected over a Fiber connection on 6500 series switches on each side (primary link)

Site 'A' and 'B' has secondary connection from different ISP with BGP 

users in site 'A' connects over fiber to users on 'B' and if this link goes down I would want users to connect via secondary connection and only than 

so what would be the best way to accomplish this.

Internally we have EIGRP between both switches and network 

I was thinking of configuring conditional advertisment in BGP to make it work but I get stuck in a thought that I would have to convert the internal routing from EIGRP to iBGP and than make it work

Also I cannot use any other protocol because we have other sites connected to Site A users via this secondary ISP with BGP and I cannot advertise the same subnet on both side 'A' and 'B' 

Thanks in Advance

[zulqurnain]

'"Also I am neither on site A and B doing BGP into EIGRP . on Site B I am using route-map to set EIGRP local-preference 10 and weight 40 when EIGRP is redistributed into BGP and in BGP config it's weight is 40000"

means that I am not redistributing BGP into EIGRP on both site A and B and that on site B I have configure EIGRP local-preference 10 and weight 40 so that it does not take precedence over BGP routes and only preferred when BGP doesn't have that route. also at site B , BGP routes have weight 40000 set so that they will always should win. which obviously isn't happening.

• router receive EIGRP route and inject in BGP before it receives form MPLS
  • Correct
• router receives BGP advertisement form MPLS network but prefer local inject route
  • Correct
• when fibre is disconnect EIGRP route is removed and router put BGP route form MPLS in routing Table
  • Incorrect, when DF disconnects EIGRP route is injected from site B into BGP , normally it doesn't inject because BGP already has those routes because site A is redistributing them through BGP from site A
• when EIGRP route comes back it is not put in routing table because of worst administrative distance
  • I think BGP should take precedence because it has AD of 20 and EIGRP has AD of 90

[e.ciollaro]

Hi,

the problem is that path attribute are useful to choose which prefix will be preferred by BGP but not to prefer BGP over EIGRP.  If you want the EIGRP route to be always preferred you have to change the administrative distance of protocols. Then you have to be sure that EIGRP prefix redistributed in site-A are preferred over prefix redistributed in site-B. These can be done changing local preference or other BGP attribute (consider that ISP could change BGP path attribute; usually the preferred way to control BGP best path is as-prepend).

Also consider that your scenario  is time depending: if A receives EIGRP advertisement before BGP ones, then it install in its routing table EIGRP prefix and when MPLS turn on, redistributes them in MPLS and MPLS network will prefer this prefix because of the better local preference. But if BGP is turned on before EIGRP (as in case of DF failure), then A install BGP prefix in routing table and when EIGRP turn on it will prefer BGP prefix because of its better administrative distance (EIGRP prefix will never be installed in routing table). 

[zulqurnain]

I just tried that but what happened is that it failed over to secondary path but once the fiber (primary path) comes up the routes path doesn't change back. 

[mattp0002]

Build a tunnel (GRE or IPsec depends on your requirements) across the internet between A & B. 

Peer up A & B inside the tunnel in parallel with the fiber peering path using your EIGRP.

Configure EIGRP as required to prefer the fiber path over the internet tunnel path.

Done.