SNMP get reply with broadcast storm

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Aug 27th, 2007
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We are running c6513-sup720. IOS version: s72033-advipservicesk9_wan-vz.122-18.SXF9.

If we do a snmp get to the router from a host, the router is doing a broadcast ( with the reply instead of just replying to the host.

Any ideas ?

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Overall Rating: 2 (1 ratings)
jreekers Tue, 08/28/2007 - 14:29
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Hi. I'm suspecting that the address doing the polling is a network or broadcast address (typically used for discovery-type functions). Do you notice the same behavior with Ping?

Here's more info:

the IP/ping behaviour as follows:

As defined in RFC919, a Cisco device will answer to broadcast requests.

RFC919 leaves the option open for a vendor to also recognize the network address as a broadcast address and Cisco implemented it in this way.

Specific to SNMP:

The Cisco SNMP part of IOS is programmed to respond to broadcasts address (which can be used for discovery).

If you do not want this behaviour, you can use the "no ip directed-broadcast" option on an interface to disable the interface from

routing broadcast packages. This will only work if routing is done and not if the address is local. You could implement this feature on your first router/switch.

You can also implement an ACL on broadcasts addresses causing the router/switch to drop the broadcast packages.



reazulhuq Wed, 08/29/2007 - 11:22
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Thanks for the reply. We only see this behaviour during the snmp operation. Right now we have an ACL to block this but that's not an ideal solution.

It almost looks like a image bug but not sure.


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