Friday, April 15, 2011

Getting DUP! error when pinging a IP Address which uses trunked port

I have aggregated 2 ports for the external LAN and incoming LAN for my Big-IP F5 Load Balancer. Interestingly when I was pinging the IP which uses the aggregated ports of the switch, I got a

..............
64 bytes from 192.168.1.1: icmp_seq=1 ttl=64 time=12.4.8 ms (DUP!)
64 bytes from 192.168.1.1: icmp_seq=2 ttl=64 time=0.216 ms
64 bytes from 192.168.1.1: icmp_seq=1 ttl=64 time=12.4.8 ms (DUP!)
64 bytes from 192.168.1.1: icmp_seq=2 ttl=64 time=0.196 ms
.............

After a while, the DUP! disappeared. As usual I google around and notice the article which explain the phenenomen. In a nutshell, the (DUP!) is caused by

......it is a side effect of how many switches update their MAC forwarding tables. Initially, the switch does not associate the MAC address in the packet with a particular switch port, and so it may send the
traffic to all ports until its MAC forwarding table is updated.


Since the interfaces attached to the bond may occupy multiple ports on a single switch, when the switch (temporarily) floods the traffic to all ports, the bond device receives multiple copies of the same packet (one per slave device)..........

For more information, see Duplicate ping error with network bonding driver in Linux

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