Route table growth and hardware to the filter

Jon Lewis jlewis at
Thu Sep 20 23:40:31 UTC 2007

On Thu, 20 Sep 2007, Bora Akyol wrote:

>>> I was playing with a sup2 adding in extra routes to the point that it ran out
>>> of memory. Unfortunately, it didn't just drop routes like I thought it would.
>>> CEF disabled itself as well, which on a busy box would be a disaster.
>>> Is this what people expect will happen in a few months to people using sup2s?
>>> Or am I missing something else?
>> That's not good.  What software version was it running?
> While it is not good, the alternative approach would leave an indeterminate
> routing table in hardware. Would you like the packets to go to randomized
> directions?

No, but someone previously posted that with later software versions, when 
TCAM runs out, packets for those routes that fit in TCAM are hardware 
switched, and only traffic for the remaining routes that didn't fit are 
software switched.  That could potentially go unnoticed for some time, 
while software switching all traffic is likely be impossible on many 
installations.  I kind of doubt the MSFC2 can software switch gigabits/s 
of traffic (or anything close to gigabits/s).

> SUP2 was a great RP with a really long life, but maybe it is time to move on
> to a SUP720 with the large table option and then grab a cold one ;-)

Or start filtering some of the twit networks that totally deagg their 
CIDRs.  I see a game of internet chicken in the near future...only some of 
the players don't realize they're playing.

  Jon Lewis                   |  I route
  Senior Network Engineer     |  therefore you are
  Atlantic Net                |
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