[c-nsp] 7206-VXR Buffer Issue

[Brian Turnbow]

A traffic burst is most likely the cause.
The router keeps n buffers ready and creates more when needed to handle traffic bursts.
But if the burst is larger then the "ready" buffers + the amount that it can create on the fly to handle the load, you will see errors on the interfaces and "ignored packets". 
You need to tune the buffers on the router so that they are large enough to accomodate your traffic bursts. 
Check out this  
http://www.cisco.com/en/US/products/hw/routers/ps133/products_tech_note09186a00800a7b80.shtml


Brian

-----Original Message-----
From: cisco-nsp-bounces at puck.nether.net [mailto:cisco-nsp-bounces at puck.nether.net] On Behalf Of Mark Tinka
Sent: mercoledì 13 dicembre 2006 8.21
To: cisco-nsp at puck.nether.net
Subject: [c-nsp] 7206-VXR Buffer Issue

Hi all.

We have a 7206-VXR/NPE-300 experiencing 3 to 5 minute periods of 
outage on one port of a PA-2FE-TX/non-ISL port adapter. This 
happens once in every 8 or so hours.

OI (Output Interpreter) suggests the input errors on the interface 
are due shortage of interface buffers. On running 'sh buffers' 
through the OI, it says (this includes all interfaces on the 
router):

WARNING: This router has dropped 274 packet(s) (0.00016%) due to a
         shortage of 'Small buffers'.

WARNING: This router has dropped 1619 packet(s) (0.00245%) due to a
         shortage of 'Middle buffers'.

INFO: If new buffers are not available, the packets are not dropped
      but the next largest buffer size is used. So these buffer
      failures can be ignored.

This NPE-300 is equipped with 256MB DRAM. The affected port on this 
PA has a back-to-back connection to a FreeBSD machine, both running 
at an auto-neg'ed 100/full with no errors for the past several 
months until now. The FreeBSD machine is running in bridged mode to 
another router - what is interesting is during this outage, iBGP 
between the 2 routers through the bridge fails (Hold timer 
expiration), but the OSPF does not.

The router is running IOS 12.3(20) and has 144MB of free RAM.

The affected port on the PA does about 8Mbps of traffic on average. 
There are no errors on the FreeBSD machine that indicate a problem 
with the FE port on there.

All help appreciated.

Cheers,

Mark.