Yep, that i know, but my point was to know how the NAT code knows to which internal host it have to send the ICMP as we dont have port numbers in an ICMP message and only the destination address is not ok as 2 internal station could have connected to the same server. The answer was in fact that in the payload of the ICMP you have the original IP packet + 64bit of the next payload: aka the TCP header and ports --> the information is completed.
JeF On Wed, 31 Oct 2001, Matt Hyne wrote: > At Wednesday, 31/10/2001 09:55 AM (+1100), Jean-Francois Dive wrote: > >Hi all, > > > >i was wandering something with PAT: > >If you have multiple boxes trying to access the same server on the internet, > >going trough the same PAT router, so using the same external ip address: if > >the sender stack does Path MTU discovery (most of the stack does now), and > >if both hit a smaller MTU in the way, how does the NAT code knows where to > >send back the ICMP on the inside of the PAT router .? I believe it does > >work, but how ? > > All PAT/NAT does is translates the private IP address to a public ip+port via a >lookup table using the src and dst ip addresses/port numbers. > > Each session will have a different translation thus each path's MTU is retained. > > >JeF > > > > > >-- > >SLUG - Sydney Linux User Group Mailing List - http://slug.org.au/ > >More Info: http://lists.slug.org.au/listinfo/slug > > -- SLUG - Sydney Linux User Group Mailing List - http://slug.org.au/ More Info: http://lists.slug.org.au/listinfo/slug
