Reverse Telnet and cables...with a Cisco 2522

[Bravo020]

Hi, I hope that someone can point me in the right direction since I've been battling with the following problem for quite some time now and am beginning to think that I'm going crazy....

I apologise for the long message....

I have a Cisco 2522 that I would like to use as a remote access device to a number of devices within my lab. I am under the assumption that I can use reverse telnet to connect via the 8 low speed A/S serial ports to the console ports of the other devices within my lab. I realise that a Cisco 2509 or Cisco 2511 would also provide me with this ability, however as I have a 2522 I thought that it would be possible although with different cables.

I have some CAB-232FC cables (EIA/TIA-232 with DCE pin outs), which have a DB-60 to DB-25 configuration. In addition I have some DB-25 to RJ-45 adaptors and then a straight through RJ-45 cable connecting them to the console ports of my 3 other routers and 4 switches.

The DB-25 to RJ-45 adaptor has been wired as follows:

DB-25 RJ-45
2 ---------- 6 (TXD/RXD)
3 ---------- 3 (RXD/TXD)
4 ---------- 8 (RTS/CTS)
5 ---------- 1 (CTS/RTS)
6 ---------- 2 (DSR/DTR)
7 ---------- 4 (GND)
7 ---------- 5 (GND)
20 ---------- 7 (DTR/DSR)

The RJ-45 cable between the DB-25/RJ-45 adaptor and the console port of each device is a straight through cable and not a rolled or crossover cable.

From all the information that I can find on the Cisco website about the pin outs for the cables it is correct, although I am not totally 100% sure that they are since I am still unable to get a working reverse telnet from the 2522 to any of the other devices in my lab.

The configuration of the Cisco 2522 is as follows:

version 12.3
ip subnet-zero
ip host c1841 2002 172.16.0.1
ip host c1721 2003 172.16.0.1
ip host c3662 2004 172.16.0.1
ip host c2900 2005 172.16.0.1
ip host c2950G-1 2006 172.16.0.1
ip host c2950G-2 2007 172.16.0.1
ip host c2950G-3 2008 172.16.0.1
!
interface Loopback0
ip address 172.16.0.1 255.240.0.0
!
interface Serial2
physical-layer async
description Console connection to Cisco 1841
no ip address
encapsulation slip
!
interface Serial3
physical-layer async
description Console connection to Cisco 1721
no ip address
encapsulation slip
!
<snip>
!
interface Async10
no ip address
encapsulation slip
!
<snip>
!
line 2 8
no exec
transport input all
!

I'm not actually sure what the purpose of the interface Async10 is, but I can't recall entering that information, so can only assume that it appears as a result of changing the physical layer of the serial interfaces?

The output from a "show line" statement is provided below.
c2522#show line
Tty Typ Tx/Rx A Modem Roty AccO AccI Uses Noise Overruns Int
0 CTY - - - - - 2 0 0/0 -
2 TTY 9600/9600 - - - - - 3 0 0/0
3 TTY 9600/9600 - - - - - 1 0 0/0 Se3
4 TTY 9600/9600 - - - - - 1 0 0/0 Se4
5 TTY 9600/9600 - - - - - 1 0 0/0 Se5
6 TTY 9600/9600 - - - - - 2 0 0/0 Se6
7 TTY 9600/9600 - - - - - 0 0 0/0 Se7
8 TTY 9600/9600 - - - - - 0 0 0/0 Se8
10 AUX 9600/9600 - - - - - 0 0 0/0 -
* 11 VTY - - - - - 8 0 0/0 -
12 VTY - - - - - 0 0 0/0 -
13 VTY - - - - - 0 0 0/0 -
14 VTY - - - - - 0 0 0/0 -
15 VTY - - - - - 0 0 0/0 -

Line(s) not in async mode -or- with no hardware support:
1, 9

So, unless there is more information that I should have entered, I would have thought that with a command such as "telnet 172.16.0.1 2002" I would be able to make a connection via the serial port 2 of the Cisco 2522 to the Cisco 1841 that is connected to via the it's console port.

Am I doing something wrong here (obviously I must be, else why would it not work)....? The IOS that I'm running on the 2522 is : c2500-is-l.123-26.bin.

If anyone can think of where I may have made a mistake it would be greatly appreciated.

Kind regards,

[crissa]

Hi, I hope that someone can point me in the right direction since I've been battling with the following problem for quite some time now and am beginning to think that I'm going crazy....

I apologise for the long message....

[...]

Hello,
and I apologize to shorten the quote of your posting. ;-)

Nice idea! I also looking for a 2509 or 2511 router. At the moment I use a RS232 PCI Card with 16 Interfaces with a linux box. I didn't installed ser2net yet, I only use minicom and screen.

I would like to mention the Cisco documents about reverse telnet <http://www.cisco.com/en/US/docs/ios/11_3/dial/configuration/guide/dcrtelnt.html>, reverse ssh <http://www.cisco.com/en/US/docs/ios/12_3t/12_3t11/feature/guide/gt_rssh.html> and the cable guide <http://www.cisco.com/en/US/products/hw/routers/ps332/products_tech_note09186a0080094ce6.shtml>.

You configured slip on the serial interfaces. I remember that I used this protocol for a serial connection between a linux box and an Amiga, long time ago. See <http://en.wikipedia.org/wiki/Serial_Line_Internet_Protocol>.

Are your sure you can use the serial interface of your router for a console or modem connection?

HTH!
Bye, Tore

[Bravo020]

Hi Tore,

Thanks again for the reply. Currently I'm going back through the process of checking the cables and creating a new DB-25 to RJ-45 adaptor on the premise of a DTE configuration rather than a DCE configuration (no idea if this is the root cause of my issues or not...but since I'm running out of ideas I can only think that it is my cabling at fault). As for the 2522 and it's support, yes I am positive that this can be done so long as I only use the 8 low speed asynch/synch ports which would support this approach.

Hopefully I'll get to the bottom of it soon, and although a 2509 or 2511 would also perform the task they seem to be over priced on Ebay at the moment (IMHO). One other option available is to get a NM-8A/S or NM-16A/S for the 3660, but I would rather have connectivity via the 2522 since it is so much quieter than having the 3660 running as an access server!!

If and when I manage to get it up and running I'll let you know.

Thanks again, and have a great weekend.
Regards.

[Bravo020]

Well glad to say that I managed to discover the problem, apparently I needed to use a rolled cable from the DB-25 adaptor to the console port and not a straight-through cable (or I guess I can just as easily reverse the order of the wiring on the DB-25 -> RJ-45 adaptor.:D

So the outcome of this little adventure into creating cables and adaptors is that the following is an option for connecting via reverse telnet from a Cisco 2522 the following cables can be used.

CAB-232FC (DB-60) -> DB-25(F)
DB-25(M) -> RJ-45(F)
Rolled console cable or Straight Through depending upon the wiring of the DB-25 to RJ-45 adaptor.

The pinouts for the DB-25 -> RJ-45 Adaptor I used are as follows:
DB-25 ------RJ-45 -- RJ-45
w/Rolled w/Straight
5 -------- 1 -------- 8
6 -------- 2 -------- 7
3 -------- 3 -------- 6
7 -------- 4 + 5 ---- 4 + 5
2 -------- 6 -------- 3
20-------- 7 -------- 2
4 -------- 8 --------- 1

As for the configuration of the 2522 to perform reverse telnet, all the usual Cisco links provide a wealth of information i.e.: http://www.cisco.com/en/US/tech/tk801/tk36/technologies_configuration_example09186a008014f8e7 .shtml

Alternatively, search for Reverse Telnet on Wikipedia for some useful information too.