actually, an IP header can contain options which can in turn lengthen the field. The presence of these options is indicated in the IHL field ( bits 4 thru 7 in the header ) check out RFC 791 for more detail. ftp://ftp.isi.edu/in-notes/rfc791.txt one use of the IP header options is to record hop addresses as packets travel through a network. there are a number of other options defined. Same for the TCP header. there is an optional options field of 4 bytes. my quick glance through RFC 761 tells me this field never exceeds that 4 byte length, but I am not very familiar with it. ftp://ftp.isi.edu/in-notes/rfc761.txt I bring this up because most of the study materials state ex cathedra that the IP and the TCP headers are 20 bytes. Having browsed the RFC's at one time or another, I vaguely recalled the options, looked it up, and sure enough, there they are. I don't recall much study material covering the options and their uses. Chuck -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]]On Behalf Of xie rootstock Sent: Tuesday, July 24, 2001 8:46 PM To: [EMAIL PROTECTED] Subject: RE: IP header question, Fixed 20 bytes or can be more? [7:13700] IP and TCP header has 20bytes Message Posted at: http://www.groupstudy.com/form/read.php?f=7&i=13710&t=13710 -------------------------------------------------- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
