I asked a question about this last week and didn't get any replies, so I'm giving it another try. I have a 2811 that I am using to forward multicast packets to multiple destination VLANs. On one of these VLANs I am NATing the source IP addresses of the multicast packets. On this interface the checksums for the UDP packets is being corrupted about 10% of the time. About half of the corrupted packets also have the original source address instead of the NATed address. Has anyone ever seen something like this? I'm not used to seeing a router corrupt packets like that - usually the router either works perfectly or not at all. I would appreciate any help the community can provide.