Wizard-level questions

[Barry Margolin]

In article <120840 at uunet.UU.NET> rbj at uunet.UU.NET (Root Boy Jim) writes:
>All the network really guarantees you is the identity of the IP address,
>and port number.
...
>Actually, only the network part of the info is truly reliable.

Actually, none of it is *truly* reliable.  The sending host can put
anything in its source address field of the packet.  However, if a host on
a different network says that it's a host on your network it won't be able
to receive any replies, because you'll send your replies to the real host.
For TCP-based protocols this is generally good enough, because they require
an initial two-way handshake before they do anything (it's possible to put
data in the initial SYN packet, but I know of no protocols that make use of
this).  However, UDP-based protocols often work without requiring responses
(e.g. an NFS DeleteFile operation will be obeyed and then the response will
be attempted).

--
Barry Margolin, Thinking Machines Corp.

barmar at think.com
{uunet,harvard}!think!barmar