Cisco Router - ip tcp adjust-mss command
Posted on 2013-12-11
I recently replaced an old Cisco 2621 Router with a new Cisco 2911 Router for one of my customers. It was easy enough, but when I started doing speed tests and downloads I noticed that all tests were running very slow. I would plug my laptop directly into the 50mbps circuit, bypassing the 2911, and all my speed tests and downloads came back good. I was getting 50mbps, which is my circuit speed. As soon as I would plug the router back in speed tests were back down under 1Mbps. Speed and Duplex were fine, there were no interface errors, so I called Cisco TAC. They ended up issuing the command "ip tcp adjust-mss 1360" on the inside interface of the router, and like magic I was able to achieve 50Mbps downloads and speeds through the 2911 router again. Now I know the purpose of the command is to avoid packet fragmentation during the initial TCP handshake, but this is a command I have never used before. I am wondering if this is best practice, and something I should be doing on all projects in the future? Please share any thoughts you may have on this. Thanks.