What is the most standard subnet length on internet

Zartash Uzmi zartash at gmail.com
Sun Aug 2 19:04:30 CDT 2009


Since this old thread recently became alive (momentarily), and I read
through the posts, (perhaps, again!) ...

Patrick, I would like to understand why you said that routers handling 10G
traffic in DFZ are not bothered (much) by a few extra prefixes? Isn't this
counter-intuitive? For example, for the worst case packet size of 40 bytes,
a router has only 32ns to completely
process a packet (including lookup!) in order to support 10Gb/s line rates.
The higher rates leave with even smaller time, which makes me think that
it's the "slow running" routers that should not be bothered *much* by a
small increase in the number of prefixes. Or, were you referring to 10G
routers "slow running" by comparing them with 100G routers? I do not except
anyone to have such a long memory, so you may want to skim through the
following :)

Zartash

On Sat, Dec 20, 2008 at 9:37 AM, Patrick W. Gilmore <patrick at ianai.net>wrote:

> On Dec 19, 2008, at 10:48 AM, Joe Greco wrote:
>
>  As for routing table size, no router which can handle 10s of Gbps is
>>> at all bothered by the size of the global table,
>>>
>>
>> ... as long as it isn't something like a Cisco Catalyst 6509 with SUP720
>> and doesn't have a PFC3BXL helping out ...
>>
>> ... or if we conveniently don't classify a Catalyst 65xx as a router
>> because it was primarily intended as a switch, despite how ISP's commonly
>> use them ...
>>
>>  so only edge devices
>>> or stub networks are in danger of needing to filter /24s.  And both of
>>> those can (should?) have something called a "default route", making it
>>> completely irrelevant whether they hear the /24s anyway.
>>>
>>
>> A more accurate statement is probably that "any router that can handle
>> 10s of Gbps is likely to be available in a configuration that is not at
>> all bothered by the current size of the global table, most likely at some
>> substantial additional cost."
>>
>
> Good point!  I should have said "10s of Gbps and tables associated with
> default-free networks".
>
> Or are there lots of people using 6500s without 3BXLs in the DFZ?  I admit
> I have not audited every router in the DFZ, so perhaps someone with factual
> info can help out here.
>
> If not, then we're back to where we started.  The DFZ isn't worried about
> table size this cycle, and the edges can (should?) have default.  I'm sure
> that will change in a couple years, but everything always does.
>
> Oh, and before anyone jumps all over me, I am NOT implying you should
> deaggregate and blow up the table.  Just that 300K prefixes is the DFZ is
> not a reason to start filtering /24s.  Today. :)
>
> --
> TTFN,
> patrick
>
>
>



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