Path: utzoo!utgpu!water!watmath!clyde!rutgers!topaz.rutgers.edu!ron
From: ron@topaz.rutgers.edu (Ron Natalie)
Newsgroups: comp.unix.wizards
Subject: Re: Why no trailers in network ifconfig?
Keywords: trailers, network, ifconfig, vax, sun, bsd
Message-ID: <18028@topaz.rutgers.edu>
Date: 13 Feb 88 02:01:02 GMT
References: <599@acornrc.UUCP>
Organization: The Office of Mismanagement and Bean Counting
Lines: 25

The reason they are turned off is that they were nonstandard and not
all systems can handle them (this has changed, see later).  They are
a good idea in paged UNIX implemenations which are resigned to do
at least one copy of data anyhow.  They are not a good idea for other
implementations, including most gateways as they do not copy the IP
packet at all.  They expect the IP header to be in the proper place
and just diddle the local net headers and pass it to the output
network driver.

Trailers are now a standard and leaving the trailers flag turned on
in later (standard conforming) systems should be OK.  The system now
checks while ARPing if the remote system wants to do trailers and uses
them when the remote system likes, and avoids them otherwise.

-Ron

USER:  We're having a problem with our gateway.
ME:  Really?  What is it?
USER:  We just put up a Sun and now the gateway is printing Ethernet
  errors.
ME:  Hmm, sounds serious.  What kind of errors?  Interlan transmit
  register errors?
USER:  No, it was something about trailers.
ME:  Oh, was it by any chance "Trailers make me barf!"?
USER:  Oh yes, that's it!