OSPF Route Map Question.

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Jun 22nd, 2007
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Hi Folks,


(diagram attached)


I have a question regarding route maps + route re-distribution from ospf into BGP.


Our network has 3 routers + currently runs ospf between them, we have upgraded our WAN links on router2 + router3-backup link to a new MPLS solution running BGP.


The current number of ospf routes on our network is 600+


The maximum number of allowed routes on the new MPLS service is 500, if we simply re-distribute ospf into BGP we will exceed our maximum allowed routing table.


Router1 is connected to the older ATM solution, which will still be in place, and certain subnets should go down this link and not sent into the MPLS links.


All other WAN traffic should go down the new MPLS links.


I think we need to implement some ospf route maps on router1 so that ony the allowed subnets will be sent onto router2 and then onto the MPLS network.


My question is where should the route maps be placed on the network to filter the traffic between the older ATM link + the new MPLS service.


Im not sure if this is the way to go, and any comments / feedback would be much appreciated.


If you need any further information, please dont hesitate.


thanks.



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rais Fri, 06/22/2007 - 04:55
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Apparently, OSPF is being redistributed to BGP on Router2 and 3. This is where route-maps can be added to redistribute only the selected routes.


However, the 500 route limit should be what you can send to your MPLS provider. You can use 'network' statement under BGP to control that limit + you can summarize your routes as they are sent to the SP.


Thanks.

bvsnarayana03 Fri, 06/22/2007 - 05:00
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If u hv hub locations connecting to MPLS cloud, then u may chk aggregating the n/w at hubs prior to sending them to ISP.


Aggregation of routes is the best method for you.

sundar.palaniappan Fri, 06/22/2007 - 14:10
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If router2 & router 3 need not have to learn those networks that you would want to route via the router1's ATM link then you can filter the OSPF routes on router2 & router 3 from being installed in the routing table using distribute list. This way only the OSPF routes in the routing table on router 2 & 3 would be redistributed into BGP.


HTH


Sundar

sdoremus33 Sun, 06/24/2007 - 06:54
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I agree you can aggregate @ the dist level of your network that points to your ISP

Pavel Bykov Sun, 06/24/2007 - 08:04
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I'd try to aggregate routes going to MPLS as much as possible.


You can do it using "network" and "aggregate-address" statements under BGP.


All filters should definitely be done on BGP/OSPF interface. As was mentioned, use distribute-lists when redistributing into BGP.


http://www.cisco.com/en/US/customer/products/sw/iosswrel/ps1835/products_command_reference_chapter09186a00800ca79d.html#wp1017390


Also, quick description is here: http://www.ciscotaccc.com/kaidara-advisor/iprout/showcase?case=K13368004

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