bgp track sla

Answered Question
Jun 2nd, 2008
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We're moving from one internet connection to two and our isp is going to have us use bgp for our route advertisement. I've looked at some bgp configs, and understand how we can do failover in the event of an ISP failure, but I'm also looking to be prepared for an equipment failure on our side.


I am looking for a way to monitor my border router's access to an inside host on my network, and use that to stop it from advertising the route to the ISP.


I'm hoping to prevent the following from causing an issue:

Normal operation

ISP----BorderRouter-----Internal


Failure

ISP----BorderRouter--X--Internal


Is there a way to do this?


Thanks in advance,

Rick

Correct Answer by guruprasadr about 8 years 10 months ago

Hi RIck, [Pls Rate if HELPS]


BGP will stop advertising the Prefixes if the IGP withdraw's the prefixes.


You can use OSPF to manipulate the IGP Network using COST. If the Primary (Eg: Switch in core) fails, the fail-over will happen for Secondary Switch (Eg: Secondary Switch connected to Sec Router with Sec.. ISP). By avoiding the Cross-Connect between the Primary Router and Secondary Switch the same can be acheived.


In viceversa, if the Primary Restores, the OSPF Routes are synchronised, the COST comes into the Picture and the traffic perfers Priamry Link, since there are Cross-Connect between the Pri Switch & Sec Switch.


Hope I am Informative.


Pls Rate if HELPS


Best Regards,


Guru Prasad R

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guruprasadr Mon, 06/02/2008 - 05:38
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HI Rick ,[Pls Rate if HELPS]


If i am not wrong in understanding your Question, are you looking for a Hardware level Failover ?


Your intention to stop advertising of the HOST that access your Border Router by illegal way ?


Best Regards,


Guru Prasad R

Rick Arps Mon, 06/02/2008 - 05:42
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This would be a config failover setup. I want to be able to stop advertising my routes to my isp from my border router if it detects that it can not get to the interior of my network.

guruprasadr Mon, 06/02/2008 - 05:51
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HI Rick, [Pls Rate if HELPS]


If you are running your company with self owned registered prefixes then manipulating is more easy.


BGP always assumes your IGP (OSPF / EIGRP) works very well in a synchronised manner before injecting into the BGP Protocol. When your IGP routes are failed to inject into BGP and once the re-cheability is failed in the Internet Cloud, the routes are considered as dampened Routes.


Best Regards,


Guru Prasad R

Rick Arps Mon, 06/02/2008 - 06:04
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Prasad,


We've only got 1 class c and it will be on the inside interfaces of our border routers. I wasn't anticipating running eigrp out to these devices. We use eigrp for our 10-net, but not our routable IPs.


So BGP will only advertise what the igp has routes to? If so, I suppose I could use a static with a monitor on it.

Correct Answer
guruprasadr Mon, 06/02/2008 - 06:11
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Hi RIck, [Pls Rate if HELPS]


BGP will stop advertising the Prefixes if the IGP withdraw's the prefixes.


You can use OSPF to manipulate the IGP Network using COST. If the Primary (Eg: Switch in core) fails, the fail-over will happen for Secondary Switch (Eg: Secondary Switch connected to Sec Router with Sec.. ISP). By avoiding the Cross-Connect between the Primary Router and Secondary Switch the same can be acheived.


In viceversa, if the Primary Restores, the OSPF Routes are synchronised, the COST comes into the Picture and the traffic perfers Priamry Link, since there are Cross-Connect between the Pri Switch & Sec Switch.


Hope I am Informative.


Pls Rate if HELPS


Best Regards,


Guru Prasad R

Rick Arps Mon, 06/02/2008 - 06:21
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Thanks Prasad,


I think I've got what I need.

guruprasadr Mon, 06/02/2008 - 06:35
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HI Rick,


Welcome :-)


Regards,


Guru Prasad R

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