From: Richard Furda (riso@xxxxxxxxx)
Date: Sat Apr 06 2002 - 11:19:00 GMT-3
heh.. Let me put it this way. When cisco is acting as a DCE (thus
providing link speed or clocking if you will) it limits you to the speeds
listed in the "clock rate ?" interface/subinterface command. On some IOS
if you provide 1.5 it will round it off to 2mbps, why? well because.
In order to provide 1.544 you must use some other methods to get the
desired speed. On the IP layer you have a choice between rate-limiting or
shaping. 'clock rate #' is more of a L1/layer2 thing.
Rich
On Sat, 6 Apr 2002, thomas larus wrote:
> Okay. I think we all know this by now. 1) The clock rate comes from the prov
ider, and 2) The bandwidth command is for calculations done by routing protocol
s.
> <p>
> I am sorry to sound testy, but could someone just tell me what clock rate he
or she uses when they want the interface to carry 1.544000 mbps in a lab scenar
io. I understand that in the real world it is all different. I think the an
swer is 2000000, but could someone confirm this?
>
> I would like to resolve this simple-seeming question so I can move on to oth
er, more important questions that I need to resolve, like why does my router ig
nore the fact that I configured BC as 8000 and insist that BC is exactly one-th
ousandth of CIR, or, why is it that in a Solie chapter on FRTS, the router deci
ded that the interval for the serial interface was 125 ms (which makes sense),
but that the interval on the subinterfaces was exactly 12.
>
> I figured that setting my clock rate to 1300000 might have been messing up my
"sh traffic" and "sh frame pvc" figures, and that's why I asked about somethin
g so basic.
>
>
>
>
>
> >>> Richard Furda <riso@furda.net> 04/06/02 15:29 PM >>>
> In real life situations, you have a CSU/DSU providing the clocking
> information and the serial interface on a router (being a DTE) would pick
> it up.
>
> Rich
>
>
> On Sat, 6 Apr 2002, thomas larus wrote:
>
> > I know it's not a legal option. That's my point. That's what my screen ou
tput was there to remind us all of. My question is, what clock rate should I us
e for an interface that I want to be the same as a real-life T1, that is 154400
0.
> >
> > I have a feeling I am worried about something that simply does not matter.
Otherwise, lots of people would have wondeed about this and there would be fif
ty ready, right-on-point answers in five minutes, like the old "no peer neighbo
r-route" answer that we see every few days in answer to questions about ip ospf
demand-circuit.
> >
> >
> >
> > >>> "Narvaez, Pablo" <Pablo.Narvaez@getronics.com> 04/06/02 14:07 PM >>>
> > ummmm If you do a "show controll ser x" do you see that speed as a legal op
tion? ..
> >
> > R7(config-if)#clock rate 1544000
> > Unknown clock rate
> > R7(config-if)#clock rate ?
> > Speed (bits per second)
> > 1200
> > 2400
> > 4800
> > 9600
> > 14400
> > 19200
> > 28800
> > 32000
> > 38400
> > 56000
> > 57600
> > 64000
> > 72000
> > 115200
> > 125000
> > 128000
> > 148000
> > 192000
> > 250000
> > 256000
> > 384000
> > 500000
> > 512000
> > 768000
> > 800000
> > 1000000
> > 1300000
> > 2000000
> > 4000000
> > 8000000
> >
> > <300-8000000> Choose clockrate from list above
> >
> > R7(config-if)#clock rate 2000000
> >
> >
> > cheers,
> >
> > hockito
> >
> >
> >
> >
> >
> >
> > -----Original Message-----
> > From: thomas larus [mailto:tlarus@mwc.edu]
> > Sent: Sabado, 06 de Abril de 2002 12:58 p.m.
> > To: Narvaez, Pablo; ccielab@groupstudy.com
> > Subject: Re: RE: What is relation between clockrate and bandwidth?
> > Common port speed 1544000, but no clock rate like
> >
> >
> > I understand that the bandwidth command is for routing protocol purposes.
> >
> > I am sorry that my question seeme to be about the bandwidth command. My qu
estion is about the relations between clock rate and the real bandwidth on the
interface. I want an interface to be configured to be able to really carry 154
4000 mbps. I should think that to do this I would need to set a clock rate on
the interface of a that speed or a little bit higher, but that clock rate is no
t an option.
> > You said:
> > " For the lab, you may configure the clockrate as you wish as long as both
ends match. Just keep in mind that the bw will be responsable for the routing p
rotocol decisions ..."
> >
> > I just tried to set the clockrate to 1544000,and it would not let me. (We
have all tried to do this at some point, probably.)
> >
> >
> >
> > r2613(config-if)#clock rate ?
> > Speed (bits per second)
> > 1200
> > 2400
> > 4800
> > 9600
> > 14400
> > 19200
> > 28800
> > 32000
> > 38400
> > 56000
> > 57600
> > 64000
> > 72000
> > 115200
> > 125000
> > 128000
> > 148000
> > 192000
> > 250000
> > 256000
> > 384000
> > 500000
> > 512000
> > 768000
> > 800000
> > 1000000
> > 1300000
> > 2000000
> > 4000000
> > 8000000
> >
> > <300-4000000> Choose clockrate from list above
> >
> > r2613(config-if)#clock rate 1544000
> > Unknown clock rate
> >
> >
> > So which clock rate setting should I use in a home lab scenario setting w
here I am trying to emulate a DS-1 of 1544000. Should I use clock rate of 20000
00? What do other folks use? This must be a question lots of you have had, an
d found an adequate, and perhaps obvious answer.
> >
> > Thanks for the excellent point about frame relay multipoint.
> >
> > Thanks in advance.
> >
> > Tom Larus
> >
> >
> > >>> "Naraez, Pablo" <Pablo.Narvaez@getronics.com> 04/06/02 13:29 PM >>>
> > The bandwith command if for routing protocols only, not for layer1 bandwith
/speed nor to indicate the rate of the line clock. You may have a clock rate of
64000 and bandwith of 128k; most of the time you may want to set both at the s
ame rate in order for the routing protocol to work properly and calculate a "re
al" metric for that link,
> >
> > Some other times you may need to change that bw value, like in multipoint
sub-if with EIGRP not to overflow the low speed PVCs whereas you have to keep t
he clockrate according to the provided clock. In a real scenario, most of the t
imes you don't have to deal with clockrates in the interfaces (usually DTEs for
endpoints) since you take the clock from internal line and leave that job to t
he csu/dsu.
> >
> > For the lab, you may configure the clockrate as you wish as long as both en
ds match. Just keep in mind that the bw will be responsable for the routing pro
tocol decisions ...
> >
> > cheers,
> >
> > hockito
> >
> >
> > -----Original Message-----
> > From: thomas larus [mailto:tlarus@mwc.edu]
> > Sent: Sabado, 06 de Abril de 2002 12:02 p.m.
> > To: ccielab@groupstudy.com
> > Subject: What is relation between clockrate and bandwidth? Common port
> > speed 1544000, but no clock rate like
> >
> >
> > On my routers, I do not have the option of choosing a clock rate anywhere n
ear 1544000 (the closest rate is 1300000), yet in countless scenarios (like Sol
ie's) we set the frame relay cir to 1544000. How can we have a port speed of 1
544000 when that is never an option on our routers as a clockspeed.
> >
> > Could someone explain this.
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