Hello Jared,
We use only snmp V2.
Here is the URL
http://www.cisco.com/en/US/tech/tk648/tk362/technologies_tech_note09186a00800948e6.shtml
Jeff
On Feb 10, 2009, at 2:27 PM, Jared Mauch wrote:
On Tue, Feb 10, 2009 at 02:22:13PM -0500, Jeff Fitzwater wrote:
We are running 12.2.SXI on sup-720-cxl
We use snmp getnext and getbulk to get the ARP table from a router
that
has ~16K entries and it takes about 10min to complete, with ROUTER
CPU at
100%. Our other routers have the same hardware and IOS but have
<10K
entries and work fine.
When you say getnext/getbulk, I presume you mean a snmp v2c bulkwalk?
Or are you using snmp V1?
This is an old problem with CISCO and I thought they might have
finally
fixed it in SXI, but NOT.
The problem is the ARP entries are stored internally in a hashed
format
and SNMP needs them in an ordered format, so for every snmp PDU the
CPU
must get the entire ARP table and crunch it to create the ordered PDU
response. This will take place for as many PDUs as it takes to
retrieve
the entire table. There does appear to be a point (size of ARP
table)
at which it takes very long to retrieve the whole table which seems
to be
around 12K but with a 16K table it takes forever.
In the attached PDF from CISCO they explain the problem and also
state
the if you turn on CEF (has always been on for long time) that it is
much faster since the FIB is already in a lexical order that snmp
likes.
Since CEF is always on, why does it still take so long.
(The list strips the pdf files, you can email them to me to
post on puck, or give a pointer to the pdf on cisco.com)
At this point we basically cannot do any retrieval of the ARP
tables.
Their must be many other groups that have this same problem or I have
really missed something.
I will open up a ticket with CISCO if nobody out there has an answer.
Currently we use an expect script to get the table via CLI which is
much
faster but it doesn't help tools that must use snmp.
Thanks for any help.
Jeff Fitzwater
OIT Network Systems
Princeton University
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Jared Mauch | pgp key available via finger from [email protected]
clue++; | http://puck.nether.net/~jared/ My statements are
only mine.
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