Newsgroups: comp.dcom.sys.cisco
Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!zaphod.mps.ohio-state.edu!think.com!barmar
From: barmar@think.com (Barry Margolin)
Subject: Re: Extended access list and ports
Message-ID: <1991Mar24.183711.13366@Think.COM>
Sender: news@Think.COM
Organization: Thinking Machines Corporation, Cambridge MA, USA
References: <1991Mar21.150239.25694@sparrms.ists.ca>
Date: Sun, 24 Mar 91 18:37:11 GMT

In article <1991Mar21.150239.25694@sparrms.ists.ca> ddr@sparrms.ists.ca (Dave Rajnauth) writes:
>I have been having problems figuring out port numbers used for 
>a couple of protocols.  Specifically NFS and BIND DNS.  I have
>checked the assined numbers RFC and this has not helped very much.

Most NFS server implementations use UDP port 2049, although the RPC portmapper
may be used to relocate it to another port (but I think many NFS client
implementations don't use the portmapper, so it's unwise to relocate).
This information probably isn't in the Assigned Numbers RFC because NFS
isn't an official protocol and because of the portmapper.

The NFS Mount protocol uses UDP port 715 and TCP port 719.  Again, these
might be relocated using the portmapper.

The port for the Domain protocol is 53.  This should have been in the
Assigned Numbers RFC.  Both UDP and TCP may be used.

>I need to know which ports are used on a client.  That is when a host
>mounts a NFS server's mount point, what does the source and destination
>port fields read in the packet.  What protocols are used (ie TCP or UDP).
>For DNS which ports are used?

Clients may use any source port.  BIND appears to use port 53 as its source
port; I assume this simplifies the code, since it doesn't have to bind to a
new port for each request it sends out, and the server side of it already
has port 53 bound.  I find this behavior annoying, since it means that I
have to allow UDP packets destined for port 53 into our network, even
though the domain server we advertise is on the other side of the port
filter.
--
Barry Margolin, Thinking Machines Corp.

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