At 01:42 AM 6/21/02, John Neiberger wrote: >This isn't quite true. I agree. I think the materials Michael was looking at overgeneralized. Words like "only" and "always" just don't come into play with networks unless you're talking about the speed of light or something. ;-)
Seriously, this much I know is true: The link between the router serial interface and the CSU/DSU (which Howard tells me is really a DSU) is V.35. The router acts as DTE. The CSU/DSU acts as DCE. (We tend to think of the switch in the provider's office as being DCE which is true also, but on the local level, the DSU is acting as DCE). On a V.35 connection, this much I know is true: DTE is responsible for DTR and RTS DCE is responsible for Data Carrier Detect (CD), DSR, and CTS. Numerous things can go wrong to cause the DTE or DCE not to assert one or more of these. They have to all be asserted for the interfaces to be up/x. However, are all those things local to the V.35 endpoints and cabling? Or could a problem out the other end of the DCE (out the carrier side of the CSU/DSU) cause them not to be asserted? Could a misconfiguration of framing or encoding on an external CSU/DSU cause a problem that resulted in a down/down interface? I think from the answers that I'm getting that the answer is yes. (or at least flapping and sometimes being down/down ;-) Thanks everyone for your help. Don't I come up with some good ones? ;-) Priscilla > For example, a DCE router interface will be >down/down if DTR is not raised by the DTE device. I see this quite >often at work and faulty cabling is generally not the culprit. It's >almost always bad hardware in the DTE. > >John > >Michael L. Williams wrote: > > According to CCIE exam materials, the *only* time the serial will show > > down/down is when there is NO serial cable or a bad serial cable connected. > > So even if you have a misconfigured framing method, you should at least see > > up/down..... > > > > Mike W. > > > > "Bob Timmons" wrote in message > > [EMAIL PROTECTED]">news:[EMAIL PROTECTED]... > > > >>I can't say I've ever seen a down/up condition. Up/Down perhaps. > >> > >>I'm sure there are exceptions, but it's my belief that the router doesn't > >>care about encoding, but rather a layer-1 connection to the dce/dte > > > > device. > > > >>If the router can 'talk' to the device on the other end of the cable, you > >>should get an up/x condition, where x would depend on the csu/dsu > > > > condition > > > >>of the line. > >> > >>I don't have a csu handy, otherwise I'd check that right now. I can do > > > > that > > > >>tomorrow morning (10:30 pm est here), but you may have an answer prior to > >>that... > >> > >> > >> > >>>Hi Priscilla, > >>> > >>>I have actually had this scenario (multiple times), but due to the > >> > > Telco's > > > >>>misconfiguration. > >>>Specifically we were expecting b8zs/esf. Unfortunately I can't confirm > >>>which was configured incorrectly, but I can confirm that going through > >>>all of the different combinations available at the router you will > >>>get all combinations on the serial interface (up/up, down/up and > >> > >>down/down). > >> > >>>I can also confirm, you will not establish connectivity, regardless. I > >>>believe > >>>either b8zs/esf or sf/ami are the only valid combinations. At least that > >> > >>is > >> > >>>all I've > >>>ever worked with. > >>> > >>>Hope this helps, > >>>-TV > >>> > >>> > >>>""Priscilla Oppenheimer"" wrote in message > >>>[EMAIL PROTECTED]">news:[EMAIL PROTECTED]... > >>> > >>>>Hi Group Study, > >>>> > >>>>While writing some questions for a practice test, I found myself > >>>>questioning what I thought was the right answer. Here's the scenario: > >>>> > >>>>A Cisco router serial interface is correctly connected with a good > >>> > > V.35 > > > >>>>cable to the data port on the DSU side of a CSU/DSU. The CSU/DSU has > >>> > >>been > >> > >>>>misconfigured for the framing method (SF instead of ESF). The framing > >>>>doesn't match what the provider is using. (The question refers to a > >>> > >>>CSU/DSU > >>> > >>>>that is external to the router, not one that is built into the > >>> > > router.) > > > >>>>Will the Cisco router serial interface be down/down or up/down? > >>>> > >>>>And, would the answer be any different if the question has to do with > >>>>misconfiguring the encoding (AMI versus B8ZS)? > >>>> > >>>>If you have real-world experience with this, that would help. I have > >>> > >>read > >> > >>>>the Cisco documentation and the troubleshooting charts, etc. > >>>> > >>>>Thanks > >>>> > >>>>Priscilla > >>>> > >>>>________________________ > >>>> > >>>>Priscilla Oppenheimer > >>>>http://www.priscilla.com ________________________ Priscilla Oppenheimer http://www.priscilla.com Message Posted at: http://www.groupstudy.com/form/read.php?f=7&i=47149&t=47101 -------------------------------------------------- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
