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what is Reverse Telnet

J

JeFTuX

Junior Member


The techie guy said that we access Cisco Router using Reverse telnet

I have used telnet but dont have any idea of this Reverse telnet i have googled out but can't sort out what it i have seen some where that it is also reffered as Direct telnet

If any one knows please give the difference
 
Reverse Telnet (a Cisco term) is when you Telnet FROM the router to another device (modem or perhaps another router).

It is common to use a router (frequently with one or more 8 or 16 port async serial interfaces) to access a rack of other devices (routers, switches, firewalls, etc.). Since you are accessing the device from the console port, it is a little safer than via in-band.

FWIW

Scott
 
telnet = from network to network of interface (telnet program)

reverse telnet = from network to serial.

Commonly used on terminal servers, like a router with a bunch of asynchronous lines or modems....allows you to get to individual lines with a terminal program (telnet)

"telnet locahost 2002"
 
Thnks ScottMac & spidey07

So it basically starting telnet to another router from Cisco IOS CLI .
This bring me to another point .Even after blocking telnet port 23 using Access List i was able to access telnet from another IOS CLI but not from Normal Pc so i guess this has to do some thing with reverse telnet or is it some thing else like IOS CLI uses some different telnet port or so...
 
It would depend on where you applied the ACL. If you applied it to the inbound Ethernet port, then Telnetting from that router outbound would still work (it's "behind" the blocking ACL).

If you applied it to the outbound interface to the other router, it should block the traffic, but you'd still be able to telnet into the first router.

You can apply an acl to both directions (you get one ACL, per direction, per protocol - IP, IPX, AppleTalk ...).

Regarding Reverse Telnet:

Here's a few thousand examples.

FWIW

Scott
 
12 routers back to back?

Just use a 16 port asycn card and attach to the aux ports on the other 12 routers.

Its kinda common to use something like this to have console access to all routers (in case you can't reach them, processor thru the roof, etc)
 
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