Ethernet Switches & Routers

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Occasional Contributor
Posts: 17
Registered: ‎02-11-2013

BGP Prefix Announcement Issue

Hi everyone,

I'm having a weird issue.  Here is the setup.  We have 2 SX's. 

SX01 --->  ISPA

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SX02 --->  ISPB

I have a /24 from ISPA and another /24 from ISPB.  Both /24's are able to be announced to each of the providers.

iBGP runs between the two SX's and eBGP is being used from each of the SX's to the respective ISP.

So, I have the following on the SX's:

ip route 1.1.1.0/24 null0

ip route 2.2.2.0/24 null0

I also have prefix-lists configured for each of the /24's and configured the bgp neighbors to make use of the prefix-lists. 

My problem is that whenever I add the above null routes to both routers at the same time, I get connectivity issues and complete packetloss.  I've tried changing the administrative distance on these static routes but with no luck.  If I only add these null routes to one of the SX's and remove them from the other, then the prefixes get announced fine to the respective ISP and things work fine.

Any ideas how to fix?  On cisco devices, it's as simple as adding the above commands to both edge routers so not sure why this isn't working at the moment.

Thanks

Occasional Visitor
Posts: 1
Registered: ‎06-12-2012

Re: BGP Prefix Announcement Issue

A couple of options to resolve this (if it hasn't already been resolved):

Add a metric to your null routes (this is the same as what is required on a Cisco device):

ip route 1.1.1.0/24 null0 255

ip route 2.2.2.0/24 null0 255

If you put that in place on both SXes, that should work.

Another option is to simply configure aggregate routes, under BGP:

SX(config-bgp)# aggregate-address 1.1.1.0 255.255.255.0

SX(config-bgp)# aggregate-address 2.2.2.0 255.255.255.0

Either of these options will work, for they are essentially doing the same thing. The lack of the metric is what was gumming up the works for you before, for the router will prefer static routes, unless they are given a higher metric.

I hope that helps you out.

Regards.

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