any dangers of filtering every /24 on full internet table to preserve FIB space ?

Owen DeLong owen at
Sun Oct 16 21:08:46 UTC 2022

This situation isn’t helped by RIR policies that require you to announce the aggregate in region even if the more specifics are scattered around the world. 

The whole territorial exclusivity game played by some RIRs may well cause more harm than good at this point.

Yes, I realize this is a reversal of my previous views on the subject. I’m becoming more aware of more circumstances in which this idea is fraught and causing problems for legitimate users more than for policy forum shoppers and leasing companies. 


> On Oct 16, 2022, at 01:01, Matthew Petach <mpetach at> wrote:
>> On Tue, Oct 11, 2022 at 7:03 PM William Herrin <bill at> wrote:
>> On Tue, Oct 11, 2022 at 5:32 PM Matthew Petach <mpetach at> wrote:
>> [...]
>> All TCP/IP routing is more-specific route first. That is the expected
>> behavior. I honestly don't fathom your view that BGP is or should be
>> different from that norm. If the origin of a covering route has no
>> problem sinking the traffic when the more-specific is offline, I don't
>> see the problem. You shouldn't be taking them offline with route
>> filtering.
> *facepalm*
> Right.  That's the entire point I started off the subthread with.
> The problem lay with an organization that *did* have a problem
> sinking the traffic when the more-specific was not available.
> They had chunked up their allocation into smaller pieces 
> which were distributed to different island locations with no 
> internal network connectivity to the island sites.
> They were announcing a covering prefix for all the more 
> specifics, where the covering less specific announcement 
> had no reachability to the more specifics; so when a network 
> filtered out the more specifics, the traffic fell on the floor, because 
> it was sent to a location that was announcing the supernet that 
> had no reachability to the correct destination. 
> Their assumption that *everyone* would hear the more specifics, 
> and thus the traffic would flow to the right island location was the 
> "failure to understand BGP" that I was commenting on, and noting 
> that while it is entirely correct to decide if you want to filter prefixes 
> of an arbitrary length from entering your network, you may discover 
> in the process that other networks that do not understand BGP and 
> routing in general may complain that you have Broken The Internet(tm)
> by doing so.
> Assuming that your announcement of more specifics will always pull 
> traffic away from a less-specific announcement is overly-optimistic.
> While it may *often* work, you should still be prepared to deal with 
> traffic arriving at your least-specific announcement as well.
> This turned out to be something that not every network on the
> Internet fully grasps, and my original message was warning that 
> filtering on /24s would potentially bring complaints from networks 
> like those.
> It took a roundabout path, but I'm glad we eventually both ended 
> up at the same place.   :)
> Thanks!
> Matt
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <>

More information about the NANOG mailing list