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Serial Is Up, Line Protocol Is Down (looped)


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#1 ado

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Posted 04 April 2007 - 01:45 PM

I have a P2P T1 connection from A to B. At the A location, I got "serial 0 is up, line protocol is down (looped)" at the router.
Could it be possible I am getting this because at the B location the router is not plugged to the smartjack or is it something else??
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#2 Platinim

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Posted 04 April 2007 - 02:49 PM

if u see that the line is up and protocol is down, you are experiencing a clocking (keepalive) or framing problem.Check the keepalives on both ends to make sure that they match, that the clock rate is set, if needed, and that the encapsulation type is the same on both ends.The output would be consider a Data Link Layer problem.

Cheers!!!

Vaib...
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#3 ado

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Posted 04 April 2007 - 02:56 PM

The encapsulation is set to ppp on both ends. At A location, the clock source is set to line and at B location the clock source is set to internal. There is a loop exist in the circuit.
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#4 Platinim

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Posted 04 April 2007 - 09:49 PM

when u see this type of problem serial is UP and protocol is DOWN.

Pl check

1 Missing Clock.
2 Mismatch encapsulation type.
3 keepalive not being received.

Cheers!!!

Vaib...
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#5 masilamanister

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Posted 04 April 2007 - 10:10 PM

hai

check the encapsulation first
then change that encap from ppp to hdlc or if it is in hdlc means from hdlc to ppp..
then refresh that by chek the interface..
finally change the encap to the original state..
now chek the interface.. it will show up..

ya surely cos today i posed the same problem..

then other possibilities are
chk keepalives secs
chk clock rate..
:D
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#6 cyclodextrin

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Posted 04 April 2007 - 11:01 PM

If your still having issues, it may be worthwhile shutting the interface down and reconfiguring both interfaces from scratch and then bringing them up.

sounds to me like either an encapsulation issue or clocking.

:ph34r:
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#7 bilgisayar

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Posted 05 April 2007 - 02:03 AM

Are you sure it says serial is UP and protocol is DOWN ( looped) OR serial is UP and protocol is UP (looped)

just to make sure.
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#8 jeferson

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Posted 05 April 2007 - 02:12 AM

Are you sure it says serial is UP and protocol is DOWN ( looped) OR serial is UP and protocol is UP (looped)

just to make sure.


yep this looks like a l2 problem, check that configuration stuff that the guys above said.
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#9 malabow

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Posted 05 April 2007 - 02:45 AM

GUYS this is expected behaviour when the encap is not HDLC, you must have looped one of the controller, please check the if there is loop on the circuit ( if this is lab make sure you didn't loop) if you wish to see U/U (looped) then change the encap to HDLC.
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#10 faisal.saleem

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Posted 05 April 2007 - 05:36 AM

Well ado u asked a v interesting question. I agree all of you.Here is the some more details as per my practicle experience(which you very rarely seen in books).

If you purchase an E1/T1 or some like that leased lines P2P circuit from your local TELCO.They will give you point to point connectivity but the media isn't directly installed their are many hops between 2 end points.Here is just an example to more explain hopefully it will help for many persons who currently are not doing any WAN job.

Router A(T1 Serial int)-----X--------Point 1-------------point 3-------X-------(T1 Serial int)Router B

--------User Area-----------{----------------TELCO MEDIA---------------}------User Area-----

Case 1 (How to give Hard Loop in troubleshooting Leased Lines):-

Suppose your Serial int down and shows as

Serial Is Down, Line Protocol Is Down

Definitely you have Layer1 problem so you 1st check your serial interface by putting a loop cable in your serial interface of Router A.After that check the interface if it shows as

Serial is up, Line Protocol is up (looped)

Its mean your router serial interface is OK so now put your whole media chart in front of you and then call to TELCO and say as "Hey give loop to my this E1/T1 leased line on point A" the telco technician simply disconnect your leased line which is going to point B end and short the pairs of transe and receive which are goin to Router A serial interface.Now if u get loop its mean that their is no problem at point A so you go and test Point B and by this way you can actually findout where the Layer 1 problem exists.

Case 2 (How to give Soft Loop in troubleshooting Leased Lines):-

If you are getting any flapping(up and downs continuously),encapsulation errors or lots of CRCs etc on your serial interface then you try soft loops as.

In softloop you put the command loopback on the remote router i mean in our case we put softloop command on Router A and check the serial interface on Router B.It should be given output as i mean this is the current status of Router B serial interface.

Serial is up, Line Protocol is up (looped)

Note:- The loopback command always loop the remote router interface

Now at Router A do a heavy size extended ping to Router B serial interface.The IP Packets travels from Router A interface and go through whole media and then reach Router B interface and then comeback so by this way you can test your media.

Case 3 (How to configure a Backup Link on 2 E1/T1 circuits):-


Router A(T1s Serial int)==2(T1s)==X=====Point 1=====point 3====X=2(T1s)==(T1s Serial int)Router B


Suppose you have 2 E1/T1 circuits and from Router A to Router B and you are using 1 path as a primary and the 2nd path as a backup.As an example you configured static routing and give a static route with less AD to primary link and higher AD to secondary link and so that when primary link go down all the traffic automatically shifted to backup link and listen you only have to choice of configure interfaces as next hop bcz if you configure ip addresses as next hop then the route will still exist in routing table even your serial interface is down.

Now suppose your primary Link got down so primary route automatically flush from routing table and your secondary link is active bcz its route is automatically appear in the routing table.Problem is that while loop testing of your primary media as i mentioned in above Case 1 then your serial of primary link will be up and your all traffic shifted on this serial bcz of lower AD in static route but this primary serial is showing looped bcz you are testing point by point to this so all the traffic will be stuck.

How to avoid this problem?

This problem can only be solved by giving "down when loop" command on primary serial interface so while loop testing when your traffic is on backup link and you give loop to primary link the primary serial shows the loop as:-

Serial Is Up, Line Protocol Is Down (looped)

This is the answer of your question.The router force the line protocol of primary serial interface to remain down even you put loop on it.I am sure it should be clear to you that where you are mistaking in your P2P circuit.

Again Thanks ado bcz today when i saw your question i also surprised and then i talked to my friend ejaz (working in other ISP) he explained me the Case 3(new for me) and now i am giving you answer as i learned from him bcz unfortunately we dont have any same client who have 2 E1/T1 circuits purchased from us, ok time here is 1 AM and i m goin to sleep Good Night :P .

*If i am wrong from any point of view then correct me plz.

Thanks

Faisal.

Edited by faisal.saleem, 05 April 2007 - 08:52 AM.

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#11 faisal.saleem

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Posted 05 April 2007 - 08:31 AM

Case 1 (How to give Hard Loop in troubleshooting Leased Lines):-

Suppose your Serial int down and shows as

Serial Is Up, Line Protocol Is Down

Definitely you have Layer1 problem so you 1st check your serial interface by putting a loop cable in your serial interface of Router A.After that check the interface if it shows as


Oh GOD i am studying and just came on sadikhov for searching something and see my post again what a big mistak i have been made and my 6th sense was also saying me at tht time,and still nobody pointed me that "hey wht the hell u write that Serial is up line protocol is down and is it layer 1 issue?"

I am v sorry it was just my typing mistake and now i edit it again.Please if you see anywhere that your book is saying that but you are seeing that then always trust on books bcz they cannot be wrong.OK in return on this my mistake enjoy these 2 imp commands,may be many people knows about it,

"do" Coomand:-

We know that many commands like show command can only be run on privilage mode but by using do command you can force the router to do what you wnt for example

R<conf>int s0
R<conf-if>#do show version

this is very helpfull if you want something to know by show command and you dont need to back and then again go to any router / interface mode.

"inc" Command:-

If your router have a long running-config i mean composed of thousands of lines and you want to search a specific word then you can search it by simple as

R#show run | inc line vty

the router will ignore whole configurations and display you only lines which matched the key word " line vty" so by this you directly see the end of configuration where line vty configuation is present.

Note:-Recent IOS supports these commands.

Edited by faisal.saleem, 05 April 2007 - 09:14 AM.

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#12 amol0009in_7

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Posted 05 April 2007 - 11:29 PM

faisal.saleem Wow i was looking for this looping knowledge since 3 weeks in google but didn't found ! Many Many thnks frm me :)


indeed a gr8 work !
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#13 shahed

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Posted 01 August 2009 - 03:55 PM

Well ado u asked a v interesting question. I agree all of you.Here is the some more details as per my practicle experience(which you very rarely seen in books).

If you purchase an E1/T1 or some like that leased lines P2P circuit from your local TELCO.They will give you point to point connectivity but the media isn't directly installed their are many hops between 2 end points.Here is just an example to more explain hopefully it will help for many persons who currently are not doing any WAN job.

Router A(T1 Serial int)-----X--------Point 1-------------point 3-------X-------(T1 Serial int)Router B

--------User Area-----------{----------------TELCO MEDIA---------------}------User Area-----

Case 1 (How to give Hard Loop in troubleshooting Leased Lines):-

Suppose your Serial int down and shows as

Serial Is Down, Line Protocol Is Down

Definitely you have Layer1 problem so you 1st check your serial interface by putting a loop cable in your serial interface of Router A.After that check the interface if it shows as

Serial is up, Line Protocol is up (looped)

Its mean your router serial interface is OK so now put your whole media chart in front of you and then call to TELCO and say as "Hey give loop to my this E1/T1 leased line on point A" the telco technician simply disconnect your leased line which is going to point B end and short the pairs of transe and receive which are goin to Router A serial interface.Now if u get loop its mean that their is no problem at point A so you go and test Point B and by this way you can actually findout where the Layer 1 problem exists.

Case 2 (How to give Soft Loop in troubleshooting Leased Lines):-

If you are getting any flapping(up and downs continuously),encapsulation errors or lots of CRCs etc on your serial interface then you try soft loops as.

In softloop you put the command loopback on the remote router i mean in our case we put softloop command on Router A and check the serial interface on Router B.It should be given output as i mean this is the current status of Router B serial interface.

Serial is up, Line Protocol is up (looped)

Note:- The loopback command always loop the remote router interface

Now at Router A do a heavy size extended ping to Router B serial interface.The IP Packets travels from Router A interface and go through whole media and then reach Router B interface and then comeback so by this way you can test your media.

Case 3 (How to configure a Backup Link on 2 E1/T1 circuits):-


Router A(T1s Serial int)==2(T1s)==X=====Point 1=====point 3====X=2(T1s)==(T1s Serial int)Router B


Suppose you have 2 E1/T1 circuits and from Router A to Router B and you are using 1 path as a primary and the 2nd path as a backup.As an example you configured static routing and give a static route with less AD to primary link and higher AD to secondary link and so that when primary link go down all the traffic automatically shifted to backup link and listen you only have to choice of configure interfaces as next hop bcz if you configure ip addresses as next hop then the route will still exist in routing table even your serial interface is down.

Now suppose your primary Link got down so primary route automatically flush from routing table and your secondary link is active bcz its route is automatically appear in the routing table.Problem is that while loop testing of your primary media as i mentioned in above Case 1 then your serial of primary link will be up and your all traffic shifted on this serial bcz of lower AD in static route but this primary serial is showing looped bcz you are testing point by point to this so all the traffic will be stuck.

How to avoid this problem?

This problem can only be solved by giving "down when loop" command on primary serial interface so while loop testing when your traffic is on backup link and you give loop to primary link the primary serial shows the loop as:-

Serial Is Up, Line Protocol Is Down (looped)

This is the answer of your question.The router force the line protocol of primary serial interface to remain down even you put loop on it.I am sure it should be clear to you that where you are mistaking in your P2P circuit.

Again Thanks ado bcz today when i saw your question i also surprised and then i talked to my friend ejaz (working in other ISP) he explained me the Case 3(new for me) and now i am giving you answer as i learned from him bcz unfortunately we dont have any same client who have 2 E1/T1 circuits purchased from us, ok time here is 1 AM and i m goin to sleep Good Night :P .

*If i am wrong from any point of view then correct me plz.

Thanks

Faisal.

dear faisal bhai,
would pls tell me how soft loop can be performed?

regards,
shahed
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#14 msaie

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Posted 15 April 2011 - 09:26 AM

i had the same problem so i used the command fram-relay intf-type DCE on the DCE end and DTE on the DTE end
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