If IP options are used, then the IP header is longer than 20 bytes. The options add a variable-length field to the IP header. They aren't used much. Record route is one such option. Each router puts in the packet its IP address. This can be useful for troubleshooting (especially when trace route is not giving accurate results), but not all routers support it. Also, it only allows 9 routers, as I recall, so can be useless on large networks. The only other IP option I can think of right now is loose and strict source routing whereby the sender specifies which routers the packet must go through. With loose, the sender specifies a subset. With strict, the sender specifies all routers. Source routing may be obsolete. RFC 1812 (requirements for IPv4 routers) would tell you for sure. By the way, this is IP source route not Token Ring source routing (ugh). Priscilla At 11:29 PM 7/24/01, anyong wrote: >Hi Group, > >Can anyone clarify for me? >IP header has a fixed 20 bytes length or can be more than this? > >Thanks > >anyong ________________________ Priscilla Oppenheimer http://www.priscilla.com Message Posted at: http://www.groupstudy.com/form/read.php?f=7&i=13715&t=13715 -------------------------------------------------- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
