Performance impact of enabling "Logging buffered 5" on a Cisco 26xx router

Posted on 2009-02-08
Last Modified: 2013-12-24

I have a Cisco 26xx router (2 WAN ports & one LAN port).

Currently logging is not enabled, so when doing "show log" nothing was shown.
There's been cases of the router flipping (think HSRP flipping) but we don't know
if it's the Telco's leased line that caused it or the router itself, thus my idea of
enabling logging.

I intend to do the following :
> show memory exec      (to get free memory)
> logging buffered Half_Free_Available Memory 5
         (level 5 messages & below, leaving out informational ones).

We have 2 x 2Mbps links connected between local site & remote site.

Pls give your thoughts whether the performance of the 2 pairs (1 pair at our end
& 2 more pairs at the other end) of Cisco routers would be affected as I'm setting
logs to use half of the available memory.

Not in time to set the logging to log to a syslog server but would doing so (to a
remote syslog) help?

Kindly give ideas what's the optimal value to set for the logging (amt of memory)
as well as the message levels (0-7 : just want to log cases of interfaces timed
out or flipping or router itself causing a HSRP switch).  What to check for CPU
(sh proc cpu?)

Basically we don't want performance to users to be affected due to logging
being enabled on routers
Question by:sunhux
    LVL 23

    Accepted Solution

    Why are you using logging buffers so large?

    I normally use 8K to  100K  buffers.
    The performance impact (if any)  should be minimal.

    I actually recommend logging to a remote server using syslog (setup a Linux or UNIX server to accept the log entries over remote syslog),  and keeping 8K of buffer on the local device.

    This way you can get at a most-recent history by logging in, while having the past week of logs on a Linux server.
    LVL 23

    Assisted Solution

    That is: the performance of enabling logging on a router is normally negligible.

    It can potentially be greater if you pump up the logging level and start enabling debugs,  but logging alone is nil,  and it's a very bad configuration to not have any logging enabled.

    Author Comment


    When I issued "show log" on the pair of Cisco 26xx, it just showed "logging on" and
    a few lines indicating the logging is enabled.  Why is that there's no logs (was expecting
    to see messages like "adjacency down", "line protocol up/down" kind of messages.

    What's the command for me to find out the existing logging settings (buffer size, message
    levels etc)

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