There are a few approaches to culling the routing table. You can do it either statically or dynamically, according to your needs. 1. Filtering based on upstream communities Slimming down the Internet routing table https://www.redpill-linpro.com/sysadvent/2016/12/09/slimming-routing-table.h... 2. Filtering based on region BGP filter for North American routes http://gregsowell.com/?p=5505 Substitute prefixes for applicable region(s). Each region is about 200k prefixes. For more granularity use a geolocation service to select prefixes and/or ASNs. 3. Using flow information to install only top routes SDN Internet Router – Part 2 https://labs.spotify.com/2016/01/27/sdn-internet-router-part-2/ https://blog.ipspace.net/2015/01/sdn-router-spotify-on-software-gone-wild.ht... 4. Aggregate the routing table According to the weekly routing table report you can aggregate announcements to about half the number of prefixes. You need to roll your own software to preprocess the BGP feed. There are some tools out there, but I couldn't find a blog post about it with a quick search. If you have one, please share! Jared On 05/15/19 13:43 +0200, Baldur Norddahl wrote:
Hello
This morning we apparently had a problem with our routers not handling the full table. So I am looking into culling the least useful prefixes from our tables. I can hardly be the first one to take on that kind of project, and I am wondering if there is a ready made prefix list or similar?
Or maybe we have a list of worst offenders? I am looking for ASN that announces a lot of unnecessary /24 prefixes and which happens to be far away from us? I would filter those to something like /20 and then just have a default route to catch all.
Thanks,
Baldur
Hi, I did this tool a few years ago to download and built ASN filter lists by region automatically: https://github.com/ipcjk/asnbuilder/releases The tricky part was to build regular expressions for devices, that don't understand number ranges. For some of our routers we (un)select ASNs manually by reading and comparing CIDR-reports to current Sflow traffic: E.g. https://github.com/ipcjk/asnbuilder/blob/master/customASN.txt will become https://github.com/ipcjk/asnbuilder/blob/master/saveTheFIB.txt Jörg On 17 May 2019, at 10:59, Jared Brown wrote:
There are a few approaches to culling the routing table. You can do it either statically or dynamically, according to your needs.
1. Filtering based on upstream communities
Slimming down the Internet routing table https://www.redpill-linpro.com/sysadvent/2016/12/09/slimming-routing-table.h...
2. Filtering based on region
BGP filter for North American routes http://gregsowell.com/?p=5505
Substitute prefixes for applicable region(s). Each region is about 200k prefixes. For more granularity use a geolocation service to select prefixes and/or ASNs.
3. Using flow information to install only top routes
SDN Internet Router – Part 2 https://labs.spotify.com/2016/01/27/sdn-internet-router-part-2/ https://blog.ipspace.net/2015/01/sdn-router-spotify-on-software-gone-wild.ht...
4. Aggregate the routing table
According to the weekly routing table report you can aggregate announcements to about half the number of prefixes. You need to roll your own software to preprocess the BGP feed. There are some tools out there, but I couldn't find a blog post about it with a quick search. If you have one, please share!
Jared
participants (2)
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Jared Brown -
Jörg Kost