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

William Herrin bill at
Wed Oct 12 15:25:39 UTC 2022

On Wed, Oct 12, 2022 at 7:54 AM Andrey Kostin <ankost at> wrote:
> 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.

Hi Andrey,

Filtering routes longer than /24 route filtering came first and is the
cause here while the RIR minimum assignment is an effect. The RIRs
stay at /24 because it would be implicitly wasteful to assign
addresses in units smaller than can be routed on the public Internet.
Of the things that would have to change to make longer prefixes
routeable on the Internet, the RIR policies are the easiest.

The /24 boundary is simply a holdover from pre-CIDR times when the
smallest routing unit was a "class C." Folks wanted to make sure CIDR
didn't make their routing woes worse, so they filtered and it stuck.

Bill Herrin

For hire.

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