Smaller than a /24 for BGP?

Masataka Ohta mohta at
Wed Jan 25 02:57:33 UTC 2023

Jon Lewis wrote:

>> Yeah, but in another couple years we'll breach the 1M mark and
>> everybody will have fresh routers with lots of TCAM for a while. If
>> that were the only issue, it'd be a matter of timing the change well.
> Everybody will need them.  Not all will get (or be able to get) them.

Wrong. For /24, direct look up of 16M entry SRAM is enough.
Updating 64K entries for /8 should not be a problem, though
you may also have 64K entry SRAM for /16.

In addition, for small number of local smaller-than-/24
prefixes, another lookup of radix tree by a smaller SRAM
(with 64K entry, we can subdivide 256 /24 into /32)
should be possible.

But, there is no need for costly and power wasting TCAM.

So far, I ignore IPv6, of course.

						Masataka Ohta

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