cisco 2811 reverse telnet

[Bruce Summers]

alright folks,

i have my 2811 setup, i can remote into the router and connect using telnet via the serial interfaces to my 2 switches...however, i cannot figure out how to toggle between the sessions...

the cntl 6 shift x merely kicks me out of the session and back to my router prompt...

how do i toggle between switch 1 and switch 2 and then to router?

bruce

[jimmyhardman · Accepted solution]

Can you telnet from one switch to the other?  If so,to one of the switches, you can end the connection by typing exit at any time. But what if you want to keep your connection to a remote device but still come back to your original router console? To do that, you can press the Ctrl+Shift+6 key combination, release it, and then press X.

Here’s an example of connecting to multiple devices from RouterA router console:

RouterA#telnet 172.16.10.2
Trying 172.16.10.2 … Open
User Access Verification
Password:
RouterB>[Cntl+Shift+6, then X]
RouterA#

[Bruce Summers]

Jimmy is correct...what i wasnt doing however, was recognizing that once i was back on my router prompt, my sessions to the other device(s) were still established.

so, as Jimmy states, make your telnet session to the device(s)

-   to toggle back to your router use

                cntrl 6 shift x

once back on the router, use

RTR#   show sessions           this tells you the number of sessions and to what devices

Conn Host                Address             Byte  Idle Conn Name
   1 switch0             172.16.1.1             0     5 switch0
*  2 switch1             172.16.1.1             0     5 switch1

To reconnect to one of the sessions, merely type the number of the session    ie...  RTR#  1

to disconnect any of the sessions, run     disconnect disconnect 1

My very basic config to establish the reverse telnet is as follows.  I'm using an HWIC 16A with a single octopus cable connecting to my devices.

SWITCH NAME RESOLUTION + Port distinguisher

ip host switch0 2050 172.16.1.1
ip host switch1 2051 172.16.1.1

interface Async0/3/0
no ip address
encapsulation slip
!
interface Async0/3/1
no ip address
encapsulation slip

line 0/3/0
session-timeout 1  output
no exec
transport input all
stopbits 1
line 0/3/1
session-timeout 1  output
transport input all
stopbits 1

What i'm not clear on is the port assignments, and maybe you can answer this Jimmy, what determines the telnet port?  For example:

My line numbers are as follows:

0/3/0   50 TTY   9600/9600  -    -      -    -    -    25      7    0/0      -
*0/3/1   51 TTY   9600/9600  -    -      -    -    -     9     30 3366798/0      -

But, in order to make a connection, i have to use the port number "2050 or 2051"....what is the significance of the "20" in front of the line number?

thanks

bruce

[Bruce Summers]

ooops...i forgot a part of my confing above...

you have to set an IP to an interface to be used for the telnet sessions....the loopback interface is recommended for this purpose

interface Loopback0
ip address 172.16.1.1 255.255.255.0

I hope this post helps others looking for answers...

I'm still not sure about that port designation, and why if your line number is (in my case) 50 and 51  that I have to use 2050 and 2051...i stumbled onto that while reading another persons post...

bruce

[Bruce Summers]

I found the answer about the "20" before the line number (or line 2050 and 2051)...

http://searchnetworking.techtarget.com/tip/0,289483,sid7_gci995449_mem1,00.html

There are two types of rotaries: rotary groups and rotary lines. Rotary groups are used to provide connection access to one or more router line interfaces. The number of rotary groups a router can support depends on the hardware and IOS version. The base TCP port for group rotaries starts at 3000. To connect to a rotary group, a reverse telnet session is established to the TCP base port plus the rotary group number. For example, if the rotary group number is 47, the connection service port would be 3047. The most common use of rotary groups is for creating a dial-out modem pool. A group of async lines attached to modems are grouped to a single connection port. Users establish reverse telnet sessions to the rotary group. Then, once connected, the rotary group routes the session to a free group member.

Line rotaries behave the same way as group rotaries, except only a single line interface is associated with a line rotary. The TCP base port for line rotaries is 2000. To connect to a line rotary, a reverse telnet session is opened to the TCP base port 2000 plus the line number. So to connect to a device attached to async line 1, the line rotary port would be 2001. To connect to the device attached to line 1, a telnet connection to one of the router's IP interfaces at port 2001 needs to be opened.

again, i hope this helps any of the newbies like myself to the reverse telnet process...

bruce