MTU size

chinmay30 · ‎08-06-2008

Hi,

We are having site to site tunnel between to sites. When users from spoke site tried to access any applications to hub site(one perticular site)the response is very slow. We have reduced MTU size on tunnel as it could be MTU related issue. But it didnt work. but when we reduced MTU size of ethernet card of any LAN machine it works. (We have configured 1400 bytes on Tunnel and 1380 on LAN machine) Could any one please explain?

Joseph W. Doherty · ‎08-06-2008

TCP performance is degraded or sometimes broken by a reduction in MTU along the path. Often tunnels reduce MTU. Best performance is maintained when the client initially uses the path's maximum MTU. Reducing the client's MTU is one way to accomplish it, but if your network device supports the "tcp mss-adjust" command, you shouldn't need to adjust the client's MTU for better performance.

Giuseppe Larosa · ‎08-06-2008

Hello Chinmay,

look at the following link that provides explanations of this problem

http://www.cisco.com/en/US/products/ps6120/products_configuration_example09186a008081e621.shtml

Hope to help

Giuseppe