Small Buffer Misses

mzinz

One of our routers is getting a lot of small buffer misses each day. Thousands.

I'm not seeing ANY medium buffer misses, so it looks like when they miss the small buffer, they hit a medium buffer without incident.

Should I increase the size of the small buffer queue to help this out? We have a lot of voice traversing this router, so that likely is the cause of so many small packets. What kind of impact will this cause?

mzinz

Anybody?

It seems like it shouldn't matter if I'm only getting small buffer misses - meaning the medium buffer picked them up, but the sheer amount still worries me.

It would be nice to configure this for the high load of small packets.

chmorin

How many misses are we talking? Can we see a "show buffers" command result?

EDIT:

Also, is the interface dropping packets because of this?

mzinz

chmorin wrote: »

How many misses are we talking? Can we see a "show buffers" command result?

EDIT:

Also, is the interface dropping packets because of this?

The interface is not dropping packets. I reset counters yesterday and it looks like I have had 5 input errors (overrun).

It is averaging between 8000-9000 small buffer misses a day. I was looking a little more closely and there are a few medium misses as well, although not many.

I'm using SolarWinds to monitor this - clear counters does not clear the 'sh buffers' statistics, so this data is over a long period of time:

Buffer elements:
1117 in free list (1119 max allowed)
571817056 hits, 0 misses, 619 created

Public buffer pools:
Small buffers, 104 bytes (total 176, permanent 70, peak 230 @ 7w0d):
150 in free list (20 min, 150 max allowed)
693246243 hits, 5994774 misses, 1594954 trims, 1595060 created
3955520 failures (0 no memory)
Middle buffers, 600 bytes (total 103, permanent 35, peak 167 @ 7w0d):
99 in free list (10 min, 150 max allowed)
1312102454 hits, 72830 misses, 24258 trims, 24326 created
51506 failures (0 no memory)
Big buffers, 1536 bytes (total 50, permanent 50, peak 95 @ 7w0d):
50 in free list (5 min, 150 max allowed)
94309350 hits, 14636 misses, 1843 trims, 1843 created
13435 failures (0 no memory)
VeryBig buffers, 4520 bytes (total 10, permanent 10, peak 16 @ 7w0d):
9 in free list (0 min, 100 max allowed)
1188277 hits, 11691 misses, 161 trims, 161 created
11690 failures (0 no memory)
Large buffers, 5024 bytes (total 1, permanent 0, peak 7 @ 7w0d):
1 in free list (0 min, 10 max allowed)
170 hits, 11520 misses, 4030 trims, 4031 created
11520 failures (0 no memory)
Huge buffers, 18024 bytes (total 1, permanent 0, peak 8 @ 7w0d):
1 in free list (0 min, 4 max allowed)
194030 hits, 11449 misses, 3895 trims, 3896 created
11362 failures (0 no memory)


Edit: The VeryBig/Large/Huge misses are all from a long time ago.

chmorin

You might want to tweak your permanant buffer number. I'm not 100% sure, but you could try referancing this document for more information:
Understanding Buffer Misses and Failures [Cisco Interface Processors] - Cisco Systems

networker050184

What type of router and IOS? What type of link is on the interface?

mzinz

networker050184 wrote: »

What type of router and IOS? What type of link is on the interface?

Cisco 3845. FastEth on one side and GigE on the other side. Buffer misses are global, not interface specific (I think?)

chmorin

mzinz wrote: »

Cisco 3845. FastEth on one side and GigE on the other side. Buffer misses are global, not interface specific (I think?)

You can show the interface and see if it has any buffer problems. That may be what he is referring to.

mikej412

You can tune a piano and your router buffers, but you can't tune a fish.

If you think that additional delay of a buffer miss might add some jitter to your voice traffic during phone call rush hour -- and you've got router memory out the wahzoo -- then tweak your buffers.

But I'd guess the number of buffer misses is trivial compared to the number of packets your pumping through that router.

mzinz

mikej412 wrote: »

You can tune a piano and your router buffers, but you can't tune a fish.

If you think that additional delay of a buffer miss might add some jitter to your voice traffic during phone call rush hour -- and you've got router memory out the wahzoo -- then tweak your buffers.

But I'd guess the number of buffer misses is trivial compared to the number of packets your pumping through that router.

That's what I figured

I will tweak it, thanks everyone.

jason_lunde

mzinz wrote: »

That's what I figured

I will tweak it, thanks everyone.

You could try letting the router adaptively tune the buffers...

buffers tune automatic

if the router supports it...