From: John Beckett 

"Geo"  wrote in message
news::
> Then what is this discussing?
> http://www-mice.cs.ucl.ac.uk/multimedia/misc/tcp_ip/8810.mm.www/0098.html

It is what I was saying about a DNS query. Imagine that I send a query for
www.nls.net. Your DNS server could send a 50K byte reply (listing 200
alternate IP addresses and additional info). My DNS server would have to
have a buffer that could hold the entire 50KB message, and it would have to
send it to me, and my client would need a buffer that can hold the 50KB
message.

The fact is that my client doesn't want your reply if it is that big. My
client (probably) will NOT allocate a 64KB buffer to receive a DNS reply.
My DNS server certainly won't want to allocate these buffers for every
idiot who is doing a query at the moment.

Therefore, it is a matter of judgement as to how large a buffer should be
allocated. There is no specification for this. An IP datagram (and a UDP
packet) *could* be up to 64K bytes, but the application may not want to
handle that size. The RFC in your URL is saying that if you are sending a
datagram to a random host, you may assume that 576 bytes will fit in the
host's buffer. Anything more than that is at the discretion of the
receiver.

John

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