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icmp unreachables and secondary ip addresses on MSFC2

when configuring secondary ip addresses to vlan interfaces on an MSFC2 ip unreachables are disabled automatically. when reinstalling the unreachables there is a message like this:

ip secondary address exists, may affect IP HW switching between subnets

within the same vlan - out of sequence packets could occur

can somebody describe me a real network situation when these out of sequence packets could occur ? is the command just entered for protection of the MSFC2 or are there any real threats that have slipped my mind ?

(i do NOT use any ACLs on the interface, there is a document out that describes scenarios with ACL that I completely agree with).

thanks for any input.



Re: icmp unreachables and secondary ip addresses on MSFC2

As an example for a situation, when out of sequence packets can occur, using per-packet load balancing to share the traffic load across available paths to a given destination can cause out-of-sequence packets in a particular data flow. This can result in unsatisfactory data transmission for video and voice streaming.

I guess the issue with MSFC2 ip unreachables has been documented, you could look for bugs related to the same. Removing the secondary seems to be the only option, especially if it will not be an issue to reconfigure. I don't think there is any other way to ensure that out of sequence packets will be seen with the secondary ip's configured.

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