Re: [c-nsp] MTU issue on a GRE tunnel
Hi, mss should be mtu - 20 - 20 (IP and TCP headers). So try using ip tcp adjust-mss 1436. Best regards, Jan On 5. 5. 2010 1:18, ML wrote: I setup a GRE tunnel between two locations served by a Comcast business class cable modem. Config example. The remote end is the same. Tunnel73 ip address yy.yy.yy.yy 255.255.255.252 ip mtu 1476 ip tcp adjust-mss 1460 tunnel source x tunnel destination z tunnel path-mtu-discovery The two tunnel endpoints are ME3400s. I expected that this configuration would reduce the quantity of fragmentations needed by the router but looks like IP Input was up to around 20%. The user experience was bad since most web pages would fail to load. I thought ip tcp adjust-mss would signal help signal the users OSs to act appropriately given the situation. Have I missed something obvious? ___ cisco-nsp mailing list cisco-nsp@puck.nether.net https://puck.nether.net/mailman/listinfo/cisco-nsp archive at http://puck.nether.net/pipermail/cisco-nsp/ signature.asc Description: OpenPGP digital signature ___ cisco-nsp mailing list cisco-nsp@puck.nether.net https://puck.nether.net/mailman/listinfo/cisco-nsp archive at http://puck.nether.net/pipermail/cisco-nsp/
Re: [c-nsp] MTU issue on a GRE tunnel
Config example. The remote end is the same. Tunnel73 ip address yy.yy.yy.yy 255.255.255.252 ip mtu 1476 ip tcp adjust-mss 1460 tunnel source x tunnel destination z tunnel path-mtu-discovery The two tunnel endpoints are ME3400s. I expected that this configuration would reduce the quantity of fragmentations needed by the router but looks like IP Input was up to around 20%. The user experience was bad since most web pages would fail to load. I thought ip tcp adjust-mss would signal help signal the users OSs to act appropriately given the situation. do fragments increase in show ip traffic | in frag? In any case, since you use ip mtu 1476, you should set the TCP MSS at 40 bytes lower (max 1436 in your case) Regards, John ___ cisco-nsp mailing list cisco-nsp@puck.nether.net https://puck.nether.net/mailman/listinfo/cisco-nsp archive at http://puck.nether.net/pipermail/cisco-nsp/
Re: [c-nsp] MTU issue on a GRE tunnel
-Original Message- From: cisco-nsp-boun...@puck.nether.net [mailto:cisco-nsp-boun...@puck.nether.net] On Behalf Of ML The two tunnel endpoints are ME3400s. I believe GRE Tunnels are not supported on ME3400. The packets hit the CPU which is not very fast on that platform. I know 100% for a fact this is the case on 3550s, and AFAIK it applies to all lower-end fix-configuration switches. Ryan Werber ___ cisco-nsp mailing list cisco-nsp@puck.nether.net https://puck.nether.net/mailman/listinfo/cisco-nsp archive at http://puck.nether.net/pipermail/cisco-nsp/
