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New Member

Big Buffer Failures and no increases to "created" counter

We are currently attempting to tune the buffers on aa 7200 series router. We have an extraordinary amount of Big Buffer failures (200,000 + per hour at times) yet the "created" field has remained at 43 since time immemorial.

I am reasonably certain of where the Big Buffers hits are coming from (Multicast replications on ATM links if that helps in any way). I'm wondering if the lack of "Created" buffers is indicating something? Perhaps the hits are spiking and not giving the router time to create them? Bad Memory? (There is 0 Failures from no Memory, FYI)

Here is a sample "show buffer" output:

Public buffer pools:

Small buffers, 104 bytes (total 148, permanent 148):

129 in free list (44 min, 211 max allowed)

63967265 hits, 1549 misses, 2167 trims, 2167 created

277 failures (0 no memory)

Middle buffers, 600 bytes (total 195, permanent 195):

193 in free list (58 min, 278 max allowed)

189331988 hits, 863 misses, 2200 trims, 2200 created

23 failures (0 no memory)

Big buffers, 1524 bytes (total 295, permanent 295):

291 in free list (88 min, 421 max allowed)

2755807295 hits, 35640817 misses, 43 trims, 43 created

25200193 failures (0 no memory)

VeryBig buffers, 4520 bytes (total 153, permanent 153):

153 in free list (46 min, 219 max allowed)

24907676 hits, 1025664 misses, 606 trims, 606 created

962505 failures (0 no memory)

Large buffers, 5024 bytes (total 18, permanent 18):

18 in free list (5 min, 26 max allowed)

See the 43 in the created field? Sitting there? Mocking me?

Help? =)

  • Other Network Infrastructure Subjects
3 REPLIES

Re: Big Buffer Failures and no increases to "created" counter

Try this link as a starting point:

http://www.cisco.com/warp/public/63/bufferleak_troubleshooting.html

Hope it helps.

Steve

New Member

Re: Big Buffer Failures and no increases to "created" counter

Thanks for that Steve,

I did check that one out and it doesnt quite match my problem unfortunately. Actually, i'm not 100% sure that the static amount created *IS* a problem, but I thought I would ask .

Thanks again.

New Member

Re: Big Buffer Failures and no increases to "created" counter

Hi

I got the same pb as you except that the "created" number that is mocking me is ZERO as the failures keep increasing (and 0 no memory)

I found this in Cisco doc :

"How Buffers Are Handled by the Router

The number of buffers "in free list" is the number of available buffers. When a buffer request comes in, a buffer from the "in free list" is allocated.

If there are no buffers available and fast switching is enabled, there is a buffer failure and the packet is dropped. When the buffer pool manager process detects a buffer failure, it "creates" a new buffer to avoid future failures.

The router does not create a new buffer if the number "in free list" equals the "max allowed" value. If there is not enough memory in the router to create a new buffer, this is recorded as "no memory." If the number "in free list" is greater than the "permanent" number, the router "trims" some excess buffers.

The number of "failures" and "no memory" are the only areas you need to worry about. Failures may occur, but these should stabilize after a while. The router creates or trims buffers as necessary to stabilize the number of failures. If the number of failures continues to increase, then buffer tuning might be necessary.

If you do not have enough memory to create new buffers, look for a buffer leak or a more general memory problem. Buffers are not created in the fast−switching path, so if the router tries to fast−switch a packet and there is no buffer available, the packet is dropped and a failure is reported. The next time the buffer pool manager is run, a new buffer is created."

I am not English native speaker so the last paragraph is still puzzling me. Is a buffer created in fast-switching mode?

I hope it will help you anyway...

And if you have a magic command (except reload) to reset buffers counters, it will be welcome

Brgds

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