Problem with Loop in MPLS

Unanswered Question
Apr 21st, 2008

Dear Mister


I have the next problem . I have a lot of routers with MPLS , bgp and Router Reflectors .


Every site have redundancy , by two PEs and two distribution Switches .


In the case when I using redistribution between EIGRP and BGP , I am filtering the routers from the PE at side with filters in Route Rflectors . I am using "EIGRP SOO" for updates from EIGRP passing to BGP .


The loop is appearing when the routes are coming from another AS BGP . In this case , the loops is formed because the route is advertised to another routers ,is redistributed from BGP to EIGRP and this route is returned to BGP .


The only way to stop this routes is by distribute-list in EIGRP , but this solution is not scalable .


How can I made these ???


Is possible to mark the routes advertised from another AS , publish to anothers PEs and stop this adertising withou using distribute-list in the distribution routers ?


Regards

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ebreniz Fri, 04/25/2008 - 11:43

"show ip cef exact-route" shows you which of the two paths is selected for a given source,destination pair. If you try other

source,destination pairs, you should see the other tunnel as well.

Please send me the following:

- show version

- show run

- sh ip route

- sh ip eigrp topo

- traceroute

- topology diagram


mheusing Thu, 05/01/2008 - 00:24

Hi Rodrigo,


As you already mentioned, one way is to use distribution lists specifying prefixes during redistribution, which presents some operational challenges. Another option being more flexibel is the use of tags. Basically you mark external routes during redistribution with a unique tag and filter routes with those tags when redistributing again.


A generic example:

R11

route-map R11Tag permit 10

set tag 11

!

route-map BlockR12Tag deny 10

match tag 12

!

route-map BlockR12Tag permit 20

set metric 1 1 1 1 1



router eigrp 65000

network 172.16.0.0

redistribute bgp 65000 route-map R11Tag



router bgp 65000

redistribute eigrp 65000 route-map BlockR12Tag


R12

route-map R12Tag permit 10

set tag 12

!

route-map BlockR11Tag deny 10

match tag 11

!

route-map BlockR11Tag permit 20

set metric 1 1 1 1 1



router eigrp 65000

network 172.16.0.0

redistribute bgp 65000 route-map R12Tag



router bgp 65000

redistribute eigrp 65000 route-map BlockR11Tag


Your metric statements may be different and the tag numbers will vary, but the idea is to have prefix indepentent filtering.


Hope this helps! Please use the rating system.


Regards, Martin

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