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

Jon Lewis jlewis at
Wed Oct 12 15:51:13 UTC 2022

On Wed, 12 Oct 2022, Andrey Kostin wrote:

> Matthew Petach писал(а) 2022-10-11 20:33:
>>  My point is that it's not a feature of BGP, it's a purely human
>>  convention,
>>  arrived at through the intersection of pain and laziness.
>>  There's nothing inherently "right" or "wrong" about where the line was
>>  drawn, so for networks to decide that /24 is causing too much pain,
>>  and moving the line to /23 is no more "right" or "wong" than drawing
>>  the line at /24.  A network that *counts* on its non-connected sites
>>  being reachable because they're over a mythical /24 limit is no more
>>  right than a customer upset that their /25 announcements aren't being
>>  listened to.
> IMO this line wasn't arbitrary, it was (and it still is) a smallest possible 
> network size allocated by RIRs. So it's just a common sense to receive 
> everything down to /24 to have the complete data about all Internet 
> participants.

Nope.  I first did some work on this topic in early 2008 and remembered 
writing a blog entry about it.

RIPE, at least back in 2008, would allocate as long as /29 from several 
/8s.  I have no idea how many sub-/24 allocations they did or what the 
recipients tried doing with the space.  Even then, despite RIPE saying 
"we'll allocate as long as /29", I set the filter cut-off [arbitrarily] at 
/24 and made sure we had defaults pointing at ISPs that had "fuller" 

And just for the record, despite having been bitten by it more than 
once, I'm very much in the camp of "if you advertise a covering 
aggregate, you're offering to get packets there, regardless of whether or 
not more specifics exist."  You have no business demanding what routes 
someone else's network receives/accepts.  All you can reasonably control 
is what you advertise and what you accept.

  Jon Lewis, MCP :)           |  I route
  StackPath, Sr. Neteng       |  therefore you are
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