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Community Member

route selection OSPF/BGP

we have three locations. location A, location B and location C.Location c is the new extension of location B, its around 100 metres so we are connecting using ethernet.we will be using the resources of location b for location c.there's going to be asa/ips module at location c, behind which 2 cisco router and layer 3 notrel switches.

Location A,B and c are also going to connect thru MPLS.we currently have ospf running internally at A and B as we also have ATM circuits for backup between we run ospf internally and over MPLS the routes are distributed using BGP.

Location C

Router1 location C----Router1 Location B over ethernet

Router2 location C----MPLS could

so we want location C to knw abt networks at loca b and a via both links.but we only want voice and other data thru go thru ethernet link to location B and only the cirtix traffic thru the MPLS clould.if either of the link fails the other shd be able to traffic everything.

we are using nortel switches as its MLT helps using ospf to have faster convergence mainly for voice traffic


Re: route selection OSPF/BGP


You have some interesting requirements ...

In such setups, one would normally choose one link as the primary for all traffic and the other as backup. However, I see that you would like to make this a function of the traffic type. The only option I see that you have is to use policy-based routing with extended ACLs that match on specific ports. Traditional destination-based routing will not help since the same destination could be routed different ways depending on the traffic type.

So can we summarise your requirements as:

- all citrix traffic is to go over the MPLS link

- everything else should go over the ethernet link

- if one link fails, all traffic should go over the other

Now, with such a setup, the general inclination will be for all traffic to use the backdoor link since the OSPF routes learned from the other sites will be preferable to the BGP-learned routes (assuming that you are redistributing all OSPF routes into BGP)...

Because you will be explicitly telling your routers where to go for each type of traffic, the configuration of PBR will greatly depend on your topology.. In fact, it is likely to be an extremely complicated exercise since the 2 links are on different routers.

You have one other option - if your Citrix servers are being used only for Citrix traffic and nothing else, then you can achieve what you want through destination-based routing. In such a case, you could inject a /32 route for the Citrix servers into BGP. Therefore, the routers at each site would have a more specific route to get to the servers and would follow the MPLS link. If that went down, they would have the less specific route learned via OSPF...

Hope that gives you some ideas - pls rate the post if it does.


Community Member

Re: route selection OSPF/BGP

Hi Paresh,

PBR was a thought but i guess it would be complicated as you mentioned since its on 2 routers.

location b to c over ethernet link, and they would in 2 seperate areas.i assume we can have control on the distribution of traffic using ABR's.if we can tag a route for citrix network with a higher cost then the bgp distributed route.but i m not sure how the convergence will work


Re: route selection OSPF/BGP


Yeah, if you can isolate the citrix traffic to particular IP addresses, you can simply use longer-length prefixes to route this traffic over the required links...

However, as you mentioned, you can also control this through your ABRs - convergence will not be an issue in either case...


Community Member

Re: route selection OSPF/BGP

Hi Paresh,

location a conecting location b using ethernet..we would be using different areas..not in same the routes coming into will be external route and we woudl be doing a summarization of the routes. location b connecting to location c and also a on mpls where all ospf routes will be redistributed into bgp and sent across.they too will external route. as i mentioned earlier at location b these are two diff routers running ospf...the router which connects to mpls could is coonected to the isp and from isp's router the routes are redistributed to ospf coming into location b.before they come in we would do the longest match.

anything we are missing


Re: route selection OSPF/BGP


Yeah, I'm pretty sure that will work. Since the prefixes learned via BGP will be longer, they will be used to get to your citrix servers. The routes learned via OSPF will be summarised and so will only be followed for any other destinations.

Just one more thing, when using multiple areas, the routes summarised from one area to another are inter-area routes, not externals...


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