Multiple default route & mult specific route

Unanswered Question
Sep 8th, 2007

Hi,

How does multiple default and multiple specific route work in MPLS platform. Example for multiple default toure, 2 internet gateways (HK and NY)- Asia sites drain out through HK and Americas sites drain out through NY. I roughly know that it has something to do with different RD on every PE, and using community tag, but it would be helpful if someone can explain a bit more. or if there are other ways to do it that would be helpful as well.

thanks,

san

I have this problem too.
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swaroop.potdar Tue, 09/11/2007 - 11:57

For MPLS VPN's as well the BGP path selection doesnt change. By the virtue of different RD's when similar routes to the same destination are installed in the RIB then the closest IGP next hop is used of them.

So in your case assigning different RD's and leaving it for the PE's to follow the closest IGP next hop would be sufficient. Unless you have some more constraints.

HTH-Cheers,

Swaroop

san-pandey Tue, 09/11/2007 - 23:46

Swaroop, Thanks. While leaving it to IGP to decide maybe sufficient in some case. Any change in IGP (bandwidth upgrade etc) may have an effect on the desired path. so I was looking for a more stable solution.

thanks,

san

swaroop.potdar Wed, 09/12/2007 - 09:12

San,

if you have a concern that your IGP may or may not actually be congruent with the geography then you can tag the deafults from the respective regions and then assign a higher local preferance to the default you want to use as primary at all the PE's in the respective region.

For eg:

Asia : DEF (tag1)

NM : DEF (tag2)

PE:Asia: (tag1) local pref 200

PE:Asia: (tag2) local pref 100

and vice versa in American region.

HTH-Cheers,

Swaroop

san-pandey Fri, 09/14/2007 - 01:20

Hi Swaroop,

If all the regions are using the same AS, does the above still work?

thanks,

san

swaroop.potdar Fri, 09/14/2007 - 11:27

Hi San, I just recollected that you had a similar question in a previous post, and also understand that your question is from a end user persecptive rather than a SP persepctive.

But to choose the default which is closest in a region, also considering the bandwidth incongruency with geography, you will have to request help from the SP using the same method described above, (with community tags and assigning right local pref) for achieve the same.

If you were the SP then it would still work the same way in that case the manipulation would be done by you rather than the SP(since you would be the SP)

HTH-Cheers,

Swaroop

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