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Loopback packets on router interfaces connected to switches.

Unanswered Question
Apr 11th, 2003
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I'm viewing loopback packets on some routers interfaces directly connected to switch ports for routing between 802.1Q Vlan's. These packets are discarded by the switches, because the Source and Destination MAC addresses are the same (the mac address of the interface of the router that generates the loopback packet). I tried with severall routers (mainly 2500, 2600 and 3600) with many different IOS and is the same. I even tried a very simple configuration on the router interface with only the IP address (when i do, sh int eth 0/0, i got an answer of "loopback not set") and the loopback continue to go to the switch every 10 seconds.

What are this loopback packets? Is there a way of stopping them?

I think this is not a problem to the network, but even the less i prefer not to get this packets down to my switches.

Thank you very much in advance!!

Best regards,

Carlos Silva


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umedryk Thu, 04/17/2003 - 07:37
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Loopback packets are those which are smurfed (source IPd) from the switch and destined to the switch. so when the switch replies back to the packet, it sees that it is responding back to itself, and drops the packet.Like a clockwork, the loopback packets are sent out methodically every 10 seconds.

snitram Fri, 04/18/2003 - 13:23
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10 seconds - sounds like keepalive. Try to configure no keepalive on the interface.

Best regards, Snitram


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