Determine difference between 2 BGP feeds

David Andersen dga+ at cs.cmu.edu
Tue Apr 18 21:21:41 UTC 2006


Much of what Bill described below is already present using Nick  
Feamster's bgptools release:  http://nms.lcs.mit.edu/software/bgp/ 
bgptools/

Start with zebra / quagga / etc., which do a great job of dumping  
tables and updates.

Then use bgptools to take the MRT-formatted dumps that Zebra spits  
out and turn them into text, etc.  With the '-q' option, can insert  
the BGP updates or table snapshot directly into a SQL database.

then the libbgpdump.a library gives you lots of cool things on top of  
that.  You'd have to do a little work to get the analysis tool you  
want, but it's pretty easy.  Use the 'buildtree' starting program to  
build the prefix tree from each provider and then compare those two  
trees (see which prefixes are present/not present, see if any parts  
of the IP space are unreachable in in one and unreachable in the  
other, etc.)

It starts as Bill suggested - a read-only BGP peer from the devices,  
which takes about 3 seconds to set up.

   -Dave

On Apr 18, 2006, at 5:01 PM, Bill Nash wrote:

>
>
>
> Were I faced with this reporting equirement on an on-going basis,  
> I'd suggest establishing a read-only BGP peer with both devices and  
> comparing directly. I've got a perl BGP peering daemon that feeds  
> and maintains a mirror of the BGP routing table into SQL, applying  
> updates and withdrawals as they come in. Setting up something  
> similar, and adding some additional metrics to keep entries unique  
> by peer source would facilitate your end goal with simple SQL  
> grouping mechanics.
>
> - billn
>
> On Tue, 18 Apr 2006, Marco d'Itri wrote:
>
>>
>> On Apr 18, Scott Tuc Ellentuch at T-B-O-H <ml at t-b-o-h.net> wrote:
>>
>>> 	Is there a utility that I can use that will pull the
>>> routes off each router (Foundry preferred), and then compare
>>> them as best it can to see why there is such a difference?
>> I have one, but it's cisco-specific:
>>
>> http://www.bofh.it/~md/software/cisco-tools-0.2.tgz (the dumppeers  
>> script)
>>
>> Then you can easily find the missing routes with commands like:
>>
>> awk '{print $1}' < ../routes/1.2.3.4 | sort > ROUTER1
>> awk '{print $1}' < ../routes/1.2.3.5 | sort > ROUTER2
>> comm -23 ROUTER1 ROUTER2 > MISSING2
>>
>> -- 
>> ciao,
>> Marco
>>
>
>

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