routing design

Unanswered Question
Oct 8th, 2008

2 mpls wan link , getting terminated on 2 different routers. each router connected to a single 6509 siwtch.

so router A---6509 A and router B ---6509 B

6509 A --- 6509 B --HSRP

the routers A and B are going to exchange routes with providers routers running bgp respectively.They have thier own data path

the 6509 are LAN gateways and will do routing.

how to achieve?

preferred routing via 6509

say subnet A to use route path via router A

say subnet B to use route path via router B

also redundancy in case if

6509 A fails

6509 B fails

router A fails or the MPLS link to which it is connected

router B fails or the MPLS link to which it is connected

Which routing protocol to select

can it be OSPF between all 4 devices

or IBGP between all 4 devices and run ospf between 6509

Thanks

I have this problem too.
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Joseph W. Doherty Wed, 10/08/2008 - 16:39

Assuming your EBGP isn't Internet, you might run both OSPF and IBGP on all four routers. All four then would "know" both inside and outside topologies and there would be no need to redistribute between OSPF and BGP.

If possible, would avoid preferred paths. Likely this could be supported via PBR, but often a maintenance headache. You could consider using OER/PfR on routers A and B so that, at least for outbound, best performance path would be chosen and/or dynamically load balance outbound links.

You could also consider using GLBP on LAN 6500s instead of HSRP.

followurself Thu, 10/09/2008 - 02:43

Thanks

No its not internet

i m not sure why to use both protocols on all 4 routers. can u pls ellaborate

cant i achieve LB and failover using routing protocols, is it compulsory to use OEF/PfR

Joseph W. Doherty Thu, 10/09/2008 - 03:23

"cant i achieve LB and failover using routing protocols, is it compulsory to use OEF/PfR"

No and no. (Note your first question was a negative.)

"i m not sure why to use both protocols on all 4 routers. can u pls ellaborate "

You don't have to run both protocols on all 4 routers. You will need to run EBGP on routers A and B, I assume, to peer with external provider routers. There's probably benefit to using OSPF for your internal routing protocol. If you're going to run both protocols, your left with the issue of making internal routes known to the routers A and B and BGP external routes known to 6500s A and B. There are different ways of doing this, usually doing some form of redistribution, or you could even use statics, but if you run both OSPF and BGP on all routers, all 4 routers will dynamically "know" both the inside and outside topologies.

PS:

If you use EBGP internally, one issue that might arrise is Cisco BGP's default of only placing one path in route table. You can adjust this using multipath, but not 100% certain IBGP will then automatically install multiple paths in route table.

Giuseppe Larosa Thu, 10/09/2008 - 06:49

Hello Munaf,

just to add to what Joseph had written:

use OSPF on all four routers

have RA and RB have eBGP sessions and iBGP session between them

Have RA and RB to generate in OSPF a default-route of type O E1 in this way you can satisfy all your requirements

In normal conditions C6509A will exit via RA and C6509B via RB in case of failures the recovery will be managed by OSPF and the iBGP session.

As a plus you could have a route-map to have the O E1 default-route sent out if the eBGP session is active (check the presence of a BGP default-route with a specific BGP next-hop)

router ospf 10

default-information originate route-map check-bgp

access-list 10 permit 0.0.0.0

access-list 20 permit host

route-map check-bgp permit 10

match ip address 10

match ip next-hop 20

set metric-type type-1

set metric 50

Do this on both routers RA and RB with the correct eBGP next-hop in each case we used this for some years in a network

Hope to help

Giuseppe

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