[comp.unix.ultrix] ifconfig and trailers

schemers@vela.acs.oakland.edu (Roland Schemers III) (10/17/90)

Hello! We are running Ultrix 4.0 on various machines:VAX 6000/310, 
DECsystem 5820, VAXstation 3100's, DECstation 3100's and DECstation 5000's. 
Someone suggested that we should have a -trailers option on our ifconfig 
command in rc.local. He said it ehances network performance.

Here is part of the man page on ifconfig:

          trailers  Enables the use of a trailer link level encapsulation
                    when sending.  This is the default.  If a network
                    interface supports trailers, the system, when possible,
                    encapsulates outgoing messages in a manner that minim-
                    izes the number of memory-to-memory copy operations
                    performed by the receiver.

          -trailers Disables the use of a trailer link level encapsulation.

By intuition it seems you would want trailers. Any comments?

Thanx, Roland
-- 
Roland J. Schemers III                              Systems Programmer 
schemers@vela.acs.oakland.edu (Ultrix)              Oakland University 
schemers@argo.acs.oakland.edu (VMS)                 Rochester, MI 48309-4401
"So what's your pointer?"                            (313)-370-4323

treese@crl.dec.com (Win Treese) (10/17/90)

Disable trailers.

Win Treese						Cambridge Research Lab
treese@crl.dec.com					Digital Equipment Corp.

mathisen@dali.cs.montana.edu (Jaye Mathisen) (10/17/90)

In article <3411@vela.acs.oakland.edu> schemers@vela.acs.oakland.edu (Roland Schemers III) writes:
>Someone suggested that we should have a -trailers option on our ifconfig 
>command in rc.local. He said it ehances network performance.
>
>By intuition it seems you would want trailers. Any comments?



Somewhere, there was a large discussion about how the use of trailers
wasn't supported by all implementations of TCP/IP, and it could cause
all kinds of difficulties.

While I don't remember the specifics, we used to run with trailers here
and problems, that disappeared when we used -trailers.  I would guess
that if all you had were DEC machines running flavors of Ultrix, you
could use trailers and not have a problem, but be wary when you
mix vendors.

pavlov@canisius.UUCP (Greg Pavlov) (10/19/90)

In article <3411@vela.acs.oakland.edu>, schemers@vela.acs.oakland.edu (Roland Schemers III) writes:
> Hello! We are running Ultrix 4.0 on various machines: .........
> Someone suggested that we should have a -trailers option on our ifconfig 
> command in rc.local. He said it ehances network performance.
> 
> Here is part of the man page on ifconfig:
> 
>           trailers  Enables the use of a trailer link level encapsulation
>                     when sending.  This is the default.  ..........

  Your "somebody" was right in suggesting that you disable trailers  (tho I
  doubt that you will see very much difference in network performance: your
  cpus outrun your ethernet cards by a wide margin).  See mail on this issue
  two weeks ago: the trailers option is not all that standard anymore.

  Regarding the man page:  its one of those man pages that should have been
  revised years ago, since (in this case) it was written when systems were
  much, much slower - in all respects.


   greg pavlov, fstrf, amherst, ny
   pavlov@stewart.fstrf.org