From: Jay Hennigan (jay@xxxxxxxx)
Date: Sat Sep 15 2001 - 13:48:49 GMT-3
On Fri, 14 Sep 2001, Timothy Ouellette wrote:
> i'm familar with those commands you mentioned and also the clock rate
> command/dce or dte ends. What I'm a little unsure of is in the bootcamp
> labs, the diagram says that r7 (the frame switch) should have both it's
> s0 and s1 set as DTE. Well, when I try to use the frame route commands
> i get an error stating I cannot use this with 2 DTE devices.
There's a difference between the physical (cabling) DCE/DTE and the
logical (frame switch configuration) DCE/DTE. A frame-relay switch
has to be logical DCE to route PVCs. See details below.
The only difference between a physical DCE and DTE in terms of configuration
is that the DCE end determines the clock. So to meet the requirements of
the lab above, cable R7 with the DTE ends of the cables on S0 and S1, set
the clock rate on the connected routers, and configure the frame-relay
interface-type DCE on R7's s0 and S1 interfaces.
> So, just
> for giggles, i configured both interfaces as DCE and put both r1 and r2
> on physical serials and it worked. Now I just need to go back and
> change r1 to use a sub-int and that small part of lab should be okay.
> I'm guessing that there was maybe a typo in the lab?
You don't actually "set" the physical interface to be DCE or DTE.
within the plug end of the cable there is a shorting jumper which
the router uses to determine this. Whichever end of the link has
the DCE end of the cable requires the clock rate set.
Usually, aftermarket lab test cables are marked with DCE on one end
and DTE on the other end. If yours aren't marked, you can determine
which end is which by typing "show controller serial 0" and look at
about the second line of output. Note that as with a few other IOS
commands a space is required between "serial" and the number of the
interface. It might be a good idea to look at this and understand
it even if your cables are marked.
The router you're using as a frame-relay switch should not have
sub-interfaces configured. The routers connected to it may or may
not use subinterfaces depending on the lab requirements.
Check your layer 2 with "show frame-relay pvc".
> > on the frame switch, all your frame-relay switched serial interfaces should
> > include "frame-relay interface-type dce". Read the frame relay switch
> > configuration that I sent you very carefully. Although frame relay switch
> > config is not part of the lab, you will need to know how to read one.
This is correct.
What he is referring to here is the logical DTE/DCE distinction with
regard to frame-relay signalling. This is something that you configure
on the interface. The frame-relay switch wants to be logical DCE as
stated above. This is independent of whether the cable end connected
to the frame switch is DTE or DCE.
It is possible to have the frame switch interface set up as logical DCE
and physical DTE, in which case the connected router is physical DCE and
requires a clock rate.
Unless the lab requires otherwise, I usually connect the cables so that
the frame switch is physical DCE. As the frame switch is usually something
that you configure less frequently than the connected routers, it saves
time entering clock rates every time on the connected routers. It sounds
as if one objective of the particular practice lab you're doing is to
show that there is a distinction between physical DCE/DTE and frame-relay
logical DCE/DTE, and it sounds as if you're getting the idea.
Note that if you use CSU/DSU devices or WICs, the router is always DTE
and the clock rate is set in one CSU as internal timing with the other
one set for network timing. It makes no difference which one is internal
and which network.
-- Jay Hennigan - CCIE #7880 - Network Administration - jay@west.net NetLojix Communications, Inc. - http://www.netlojix.com/ WestNet: Connecting you to the planet. 805 884-6323 **Please read:http://www.groupstudy.com/list/posting.html
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