From: Mike Williams (ccie2be@swbell.net)
Date: Sun Jul 20 2003 - 01:00:57 GMT-3
So I'm looking at a config from a router, and I see this command
"logging queue-limit 100". I (being an uber-geek, as most here are)
have the 12.2 Master Command Index open, and I dig around, and I can't
find this command. I found "logging rate-limit" command, but not
queue-limit......
So I hop in a router, and it doesn't show up in the context help, so it
must be a hidden and/or unsupported command, right?
-------------------------------------
Router(config)#logging ?
Hostname or A.B.C.D IP address of the logging host
buffered Set buffered logging parameters
cns-events Set CNS Event logging level
console Set console logging level
count Count every log message and timestamp last
occurance
exception Limit size of exception flush output
facility Facility parameter for syslog messages
history Configure syslog history table
monitor Set terminal line (monitor) logging level
on Enable logging to all supported destinations
rate-limit Set messages per second limit
source-interface Specify interface for source address in logging
transactions
trap Set syslog server logging level
Router(config)#logging queue?
Hostname or A.B.C.D
Router(config)#logging queue-limit ?
<cr>
Router(config)#logging q?
Hostname or A.B.C.D
Router(config)#logging q ?
<cr>
-----------------------------------
I can only assume that this will set the max queue length to 100........
Here's why I bring all this up: We all know that by default all logging
goes to the 9600bps console port. Part of a reason a router "locks up"
if you do certain debugs, etc, is that the CPU gets jammed trying to
serialize all of those logging messages. I could understand the
"logging rate-limit" command reducing the amount of messages and
therefore saving the CPU from getting overloaded, but would changing the
max queue-length of the logging queue make much of a difference (i.e. if
the queue is as max length, then sure the router might drop logging
messages destined for the console port, however, the only reason this
would happen is if there are enough messages being sent to the console
that the queue backs up, and therefore once the queue is at max length,
the console port is still getting jammed, and the router would drop
logging messages until a single spot in the queue opened up, and then
and only then a single logging message would fill that final queue spot
and the queue would then be full again.) My whole point is that it
seems setting the queue max-length wouldn't keep the console port from
getting overrun with logging messages (during a heavy debug or massive
ACL with logging and lots of traffic that matched the ACL).
Any thoughts? I know my previous paragraph wasn't all the coherent, but
I hope my point/question got through........
Thanks!
Mike W.
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