Multiple Weighted BGP Routing

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Jun 25th, 2008
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Hi All,


I have an interesting problem with my current router setup that I wonder if anyone has any suggestions for.


I have two data centres both with their own /25 public IP range that peer with my ISP for BGP. For resilience I have a sub interface on the routers for the other data centre IP range with a higher weighted BGP config so if the router or link goes down the ISP will forward on to the higher weighted route (i.e. the failover DC).


All works fine and under failover conditions however I now have a requirement to be able to route externally to each data centre and of course due to the fact the router has a interface already with that range on it the packets are terminated locally. I guess what I need is for the router to ignore the locally connected backup bgp interface when routing but not quite sure how this can be achieved.


Possible solution is to use event tracking perhaps to keep track of remote IP and no shut the local interface should it go down or similar but seems a little clunky.


Does anyone have any ideas of a way forward/workaround or even document that may offer some kind of solution?


Thanks in advance.


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ruwhite Tue, 07/01/2008 - 04:43
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I think I would try conditional advertisement in this case, although it won't switch over as fast as the two advertisements being advertised all the time.


If you had a shorter prefix, you might be able to advertise a longer pair to cover the same space out either side--IE:


- 10.1.0.0/23, 10.1.2.0/24, & 10.1.3.0/24

- 10.1.2.0/23, 10.1.0.0/24, $ 10.1.1.0/24


Out either side, but since you are running /25's already, this isn't going to be possible, I don't think.


:-)


Russ

purohit_810 Tue, 07/01/2008 - 05:24
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What you need to do, You have to look on BGP multihoming feature. That will give you redudancy as well as use of both lines.


You cna easily fine Multihoming configuration examples on cisco portal.


Let me know if requirement is different.


Thanks,

Dharmesh Purohit

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