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

William Herrin bill at
Wed Oct 12 02:02:32 UTC 2022

On Tue, Oct 11, 2022 at 5:32 PM Matthew Petach <mpetach at> wrote:
> 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.

Hi Matthew,

If you defy convention in a manner which causes things that normally
work to break, your implementation is "wrong" for a fairly important
definition of "wrong."

> Let BGP work as it's supposed to work.
> If there's a covering prefix being announced, according to BGP, it's a valid pathway to reach
> all the prefixes contained within it.  If that's not how your network is constructed, don't
> send out your announcements that way.  Only announce prefixes for which you *do* have
> actual reachability.

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

Bill Herrin

For hire.

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