Priscilla Oppenheimer wrote: > > Zsombor Papp wrote: > > > > As a side question, do you think that TCP must run over IP? :) > > I forgot to comment on that very important question! :-) > > I've never seen TCP run over anything other than IP, although > in theory it could.
Has anyone seen TCP run over anything other than IP? I'm curious. > The devil is in the details though. > > Assuming no changes and compatibility with RFC 793, the RFC > that specifies TCP, TCP must run over IPv4. Check out how the > TCP checksum works. It's based partly on a pseudo header, which > includes fields from the IPv4 header. The pseudo header > contains the Source Address, Destination Address, Protocol, and > TCP length. This gives TCP protection against misrouted segments. > > So, you couldn't just plug in some other network layer and > expect TCP to work unchanged. > > So, what are the IPv6 people doing about this? Anyone know? I was hoping somebody else would research it and save me some work :-), but it wasn't too hard to research so that's OK. The RFC for IPv6, (2460) addresses the issue. It says: Any transport or other upper-layer protocol that includes the addresses from the IP header in its checksum computation must be modified for use over IPv6, to include the 128-bit IPv6 addresses instead of 32-bit IPv4 addresses. This includes TCP and UDP. And here's an interesting thing: The IPv6 version of ICMP [ICMPv6] will have a pseudo header now too. The reason for the change is to protect ICMP from misdelivery or corruption of those fields of the IPv6 header on which it depends that aren't covered by the checksum. I think this has to do with the fact that they moved a bunch of stuff from the main header to extension headers. Anyway, the concept that protocols are so modular that you can plug them in anywhere and it will still work is over-simplified. You can plug a serial interface encapsulation under anything on Cisco routers, as discussed ad nauseum, but that doesn't mean you can do it with other protocols. You can't even plug IPv6 in for IPv4 and expect TCP to work without modification! IPv6 should be lots of fun, eh? Doesn't sound as bad as the dire warnings from Howard about the current model of BGP and addressing, route churn and Internet instability, though! And on that cheery note, I will leave you for an ice-cold margarita. It's like 102 degrees in my office. I'm outta here! :-) Priscilla > > By the way, TCP was developed before IP. Most people assume the > opposite. At the time, TCP included most of IP's current > functionality. Then it was wisely decided to break them up so > that routers could do most of IP and end hosts could do TCP. In > general, the divorce went well, but there were some issues that > never got untangled completely. > > Priscilla > > Message Posted at: http://www.groupstudy.com/form/read.php?f=7&i=71576&t=71556 -------------------------------------------------- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
