Re: RMI binding to SAME port but DIFFERENT IP address on SAME host
From: Randolf Richardson (rr_at_8x.ca)
Date: 08/16/04
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Date: Mon, 16 Aug 2004 00:41:53 GMT
"Esmond Pitt <esmond.pitt@notatall.bigpond.com>" wrote in comp.lang.java:
[sNip]
>> I'm not sure if that is what you meant to imply, but there is no
>> "protocol number" field in a TCP/IP header.
>>
>> see http://mindprod.com/jgloss/tcpip.html
>>
>> The host computer simply knows which protocol it is hosting on each
>> port.
>>
>> You can't have two different protocols hosted on the same port, e.g.
>> HTTP and FTP.
[sNip]
> There is a protocol number field in an IP packet header, and I was
> talking about IP at the time. Obviously in the case of TCP the protocol
> number is the TCP protocol number, 6. BTW the statement that 'the host
> computer simply knows which protocol it is hosting on each port' needs
> further work. At the TCP level the host neither knows nor cares about
> the protocol; at the IP level you *can* have several protocols on the
> same port, e.g. ICMP, UDP, TCP.
An official list of all the protocols can be found here:
PROTOCOL NUMBERS
http://www.iana.org/assignments/protocol-numbers
Of those protocols, TCP and UDP tend to be the most interesting to
most people (probably with ICMP coming in at third place) since they are so
commonly used. Here's a list of all the port numbers used for TCP and UDP:
PORT NUMBERS
http://www.iana.org/assignments/port-numbers
Unfortunately it gets very confusing to describe these things because
the terminology is re-used. It might be easier to ask about an "IP
protocol" (e.g., TCP, UDP, ICMP, etc.), or a "TCP/IP protocol" (e.g., HTTP,
SMTP, POP3, FTP, etc.) or "UDP/IP protocol" (e.g., DNS) instead.
It's important to note that many of the protocols that are transacted
over TCP/IP and UDP/IP are sometimes supported (and recommended to be
supported) on both IP protocols. For example, you'll find that it's
possible to successfully run a DNS query over TCP/IP port 53 as well as the
usual UDP/IP port 53 on many DNS servers around the internet.
I hope this information will help to clear up some of the confusion.
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