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From: gwilliam@SH.CS.NET (George Williams)
Newsgroups: comp.protocols.tcp-ip
Subject: Re: UDP Checksumming of IP addresses
Message-ID: <9011080248.AA04564@ucbvax.Berkeley.EDU>
Date: 7 Nov 90 18:04:39 GMT
Sender: daemon@ucbvax.BERKELEY.EDU
Organization: The Internet
Lines: 22

I'm sure I've overlooked something, and could use a push..

Why does UDP (when used with checksumming enabled) create a pseudo-he
ader
that contains both the port numbers and the source and destination IP

addresses?  Isn't it already protected from address changes by the da
tagram
checksum?

/John


>Not an expert, but my best-guess-protocol-based response would be for possible fragmentation.
>If I were writing a similar protocol...would take into account the data link level transmission
>medium below IP.
 
>Sounds like the above scheme allows for just that. A datagram is so logically, right. There is
>nothing to say it has to stay physically intact....during transit. What's the real deal wizards out there ?


 George Williams