pontification bloat (was 10GE TOR port buffers (was Re: 10G switch recommendaton))
bicknell at ufp.org
Fri Jan 27 19:56:01 CST 2012
In a message written on Sat, Jan 28, 2012 at 10:31:20AM +0900, Randy Bush wrote:
> when a line card is designed to buffer the b*d of a trans-pac 40g, the
> oddities on an intra-pop link have been observed to spike to multiple
Please turn that buffer down.
It's bad enough to take a 100ms hop across the pacific. It's far
worse when there is +0-100ms of additional buffer. :(
Unless that 40G has like 4x10Gbps TCP flows on it you don't need
b*d of buffer. I bet many of your other problems go away. 10ms
of buffer would be a good number.
> so, do you have wred enabled anywhere? who actually has it enabled?
> (embarrassed to say, but to set an honest example, i do not believe iij
My current employment offers few places where it is appropriate.
However, cribbing from a previous ob where I rolled it out network wide:
random-detect precedence 0 10 40 10
random-detect precedence 1 13 40 10
random-detect precedence 2 16 40 10
random-detect precedence 3 19 40 10
random-detect precedence 4 22 40 10
random-detect precedence 5 25 40 10
random-detect precedence 6 28 40 10
random-detect precedence 7 31 40 10
vbr-nrt 6000 5000 600
service-policy output atm-queueing-out
Those packet thresholds were computed as the best balance for
6-20MMbps PVC's on an ATM interface. Also notice that the hardware
tx-ring-limit had to be reduced in order to make it effective.
There is a hardware buffer that is way too big below the software
wred on the platforms in question (7206XVR's).
Here's one to wrap your head around. You have an ATM OC-3, it has on it
40 PVC's. Each PVC has a WRED config on it allowing up to 40 packets to
be buffered. Some genius in security fires off a network scanning tool
across all 40 sites.
Yes, you now have 40*40, or 1600 packets of buffer on your single
physical port. :( If you work with Frame or ATM, or even dot1q
vlans you have to be careful of buffering per-subinterface. It can
quickly get absurd.
Leo Bicknell - bicknell at ufp.org - CCIE 3440
PGP keys at http://www.ufp.org/~bicknell/
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