It's for testing purposes. There are lots of testing situations when you
want an interface to act like it's up even if it's not sending any packets.
This isn't a case where we can do our normal thing of treating people who
ask questions like they are dumb butts. Sorry, long day.
Check this out!
charlotte#config t
Enter configuration commands, one per line. End with CNTL/Z.
charlotte(config)#int s0
charlotte(config-if)#no keep
charlotte(config-if)#loopback
charlotte(config-if)#end
charlotte#
%SYS-5-CONFIG_I: Configured from console by console
charlotte#
charlotte#
charlotte#show int s0
Serial0 is up, line protocol is up
Hardware is MCI Serial
Internet address is 192.168.40.2 255.255.255.0
MTU 1500 bytes, BW 1544 Kbit, DLY 20000 usec, rely 255/255, load 1/255
Encapsulation FRAME-RELAY, loopback set, keepalive not set
Broadcast queue 0/64, broadcasts sent/dropped 0/0, interface broadcasts 29
Last input 0:00:06, output 0:00:05, output hang never
Last clearing of "show interface" counters never
Output queue 0/40, 0 drops; input queue 0/75, 0 drops
5 minute input rate 0 bits/sec, 0 packets/sec
5 minute output rate 0 bits/sec, 0 packets/sec
69 packets input, 3077 bytes, 0 no buffer
Received 2 broadcasts, 0 runts, 0 giants
3 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored, 3 abort
74 packets output, 3708 bytes, 0 underruns
0 output errors, 0 collisions, 6 interface resets, 0 restarts
0 output buffer failures, 0 output buffers swapped out
9 carrier transitions
Of course, I doubt that my lab of MGS routers resembles anything in the
real world! ;-)
Priscilla
At 06:32 PM 11/29/01, Stefan Dozier wrote:
>Now that's a really good question!
>
>Stefan
>
>
>-----Original Message-----
>From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]]On Behalf Of
>John Neiberger
>Sent: Thursday, November 29, 2001 4:45 PM
>To: [EMAIL PROTECTED]
>Subject: Re: serial up/up w/o cable [7:27604]
>
>
>A cable-less serial interface? It's called a loopback interface. ;-)
>Which makes me wonder why the original poster was attempting this in the
>first place.
>
>Is there some functionality that he/she desires to get from a serial
>interface that is up/up without a cable that he/she couldn't get from a
>loopback interface?
>
> >>> "MADMAN" 11/29/01 12:39:00 PM >>>
>To be honest I have never tried such a thing but I thought it made
>sense that if I enabled loopback the interface should come up. I now
>tried reenabling keepalives and the interface is still up but it shows
>itself to be in the looped state:
>
>C7507MIX#sh int ser 4/1/3
>Serial4/1/3 is up, line protocol is up (looped)
>
> Which makes sense as it's seeing it's own keepalive packets come back
>via the loop.
>
> I can't do this on a 2500 either but I can't tell you why, any Cisco
>hardware engineers out there??
>
> oh well it's pretty much acedemic anyway, cableless serial
>interfaces
>are about as useful as a three legged horse.
>
> Dave
>
>Stefan Dozier wrote:
> >
> > Dave....
> >
> > If there's no cable installed in Serial4/1/3, obviously I (atleast)
> > need to broaden my level of research on why you do can accomplish
> > that feat on 7500 series routers but not on 2500 series routers!
> >
> > It's just not happening here!
> >
> > But hey....that's not a problem, don't mind expanding my horizons
>and
> > if and when I find an answer, I 'll post some feedback here.
> >
> > Thanks for the info Dave....
> >
> > Priscilla....my apologies!
> >
> > Off I go....to CCO!
> >
> > Stefan
> >
> > -----Original Message-----
> > From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]]On Behalf
>Of
> > MADMAN
> > Sent: Thursday, November 29, 2001 11:13 AM
> > To: [EMAIL PROTECTED]
> > Subject: Re: serial up/up w/o cable [7:27604]
> >
> > Tell you what, I got it to work just fine:
> >
> > interface Serial4/1/3
> > no ip address
> > no ip directed-broadcast
> > ip route-cache distributed
> > loopback
> > no keepalive
> > no cdp enable
> >
> > C7507MIX#sh int ser 4/1/3
> > Serial4/1/3 is up, line protocol is up
> > Hardware is cyBus Serial
> > MTU 1500 bytes, BW 1544 Kbit, DLY 20000 usec, rely 255/255, load
>1/255
> > Encapsulation HDLC, crc 16, loopback set
> > Keepalive not set
> > Last input never, output never, output hang never
> > Last clearing of "show interface" counters never
> > Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops:
>0
> > Queueing strategy: weighted fair
> > Output queue: 0/1000/64/0 (size/max total/threshold/drops)
> > Conversations 0/0/256 (active/max active/max total)
> > Reserved Conversations 0/0 (allocated/max allocated)
> > 5 minute input rate 0 bits/sec, 0 packets/sec
> > 5 minute output rate 0 bits/sec, 0 packets/sec
> > 0 packets input, 0 bytes, 0 no buffer
> > Received 0 broadcasts, 0 runts, 0 giants, 0 throttles
> > 0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored, 0 abort
> > 0 packets output, 0 bytes, 0 underruns
> > 0 output errors, 0 collisions, 2 interface resets
> > 0 output buffer failures, 0 output buffers swapped out
> > 3 carrier transitions
> > RTS up, CTS up, DTR up, DCD up, DSR up
> >
> > Dave
> >
> > Stefan Dozier wrote:
> > >
> > > I don't think it will Priscilla! Even with the encap HDLC,
> > > the DCD (carrier detect) control lead must be high in order
> > > for the interface status to be in an "up" condition. The
> > > only way I know to accomplish that is with a cable inserted
> > > or some type of serial loopback plug, if there's such an
> > > animal.
> > >
> > > And obviously you can't have "line protocol" in an "up" state
> > > if the interface status isn't in an "up" state!
> > >
> > > Stefan
> > >
> > > -----Original Message-----
> > > From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]]On Behalf
>Of
> > > Priscilla Oppenheimer
> > > Sent: Wednesday, November 28, 2001 7:55 PM
> > > To: [EMAIL PROTECTED]
> > > Subject: Re: serial up/up w/o cable [7:27604]
> > >
> > > At 06:52 PM 11/28/01, Tom E wrote:
> > > >How can you get a serial interface to go up/up without a cable
>connected?
> > > I
> > > >have tried loop and no keep.
> > >
> > > What's the encap? I thought this would work if you used HDLC.
> > >
> > > Priscilla
> > --
> > David Madland
> > Sr. Network Engineer
> > CCIE# 2016
> > Qwest Communications Int. Inc.
> > [EMAIL PROTECTED]
> > 612-664-3367
> >
> > "Emotion should reflect reason not guide it"
>--
>David Madland
>Sr. Network Engineer
>CCIE# 2016
>Qwest Communications Int. Inc.
>[EMAIL PROTECTED]
>612-664-3367
>
>"Emotion should reflect reason not guide it"
________________________
Priscilla Oppenheimer
http://www.priscilla.com
Message Posted at:
http://www.groupstudy.com/form/read.php?f=7&i=27755&t=27604
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