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BGP failover routing

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Nov 18th, 2011
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I need some help in BGP routing. is it possible to publish the same network in two sites which are connected using MPLS cloud? I have 10 locations, all are connected using MPLS. I have a dedicted link between 2 sites (site A and B), so that if site A MPLS link is down for some reason then the traffic shud come on dedicted link and then take MPLS link of site B.  what would be the impact if i publish the same network that site A is publishing in BGP? FYi, bot the sites has different AS numbers.



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Craig_Baum_2 Fri, 11/18/2011 - 13:56
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Are both sites to the same ISP? or different as they'd advertise your address blocks and so will only advertise the ones they own.

If different ISPs make sure you block non local IP networks to prevent becoming a transit.

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Marwan ALshawi Fri, 11/18/2011 - 15:49
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the questions are valid by the above post

however generally speaking it is for sure doable

however you need to make sure that you put the right BGP polices to influence the path selection in both direction inbound and outbound in both situation where one line is down or both are up

you can use AS prepending to effect the inbound traffic from other sites

if yo are using one AS between A and B then you can use local preference in the inbound direction to effect the outbound traffic from those sites

hope this help

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paul driver Sat, 11/19/2011 - 02:28
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To stop each AS becoming a transit AS:

ip as-path access-list 1 permit ^$

router bgp xxxx

network (isp x.x.x.x) filter-list 1 out

FYI -You could use aspath prending to effect both outbound/inbound traffic but as stated above the preferred way would to go with prepending for inbound traffic and local-preferance for outbound .



avi_krivorot Sat, 11/19/2011 - 11:47
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Although it's possible, you can't guarantee that all traffic will come to site A. Even with AS prepending. I was told that some ISPs may load balance traffic on a per packet basis to different paths. I would recommend you test this for a few weeks before implementing in production.


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