telnet from cisco router question

mungos301 · ‎03-20-2017

When I like to telnet from one to another cisco router, I have to type "telnet (eg. telnet 192.168.0.1).

I used to work in corporate network where I used IP address only to telnet to another router. I can't figure out why in my lab this not work. Routers are 2811 (IOS 15.1(1)T) and switches are 3750 (IOS 12.2(25r)SEC) and 2950 (IOS 12.0(5.3)WC(1)).

Symptoms are on all devices same. configs of one router is :

Current configuration : 3412 bytes
!
! Last configuration change at 21:02:51 UTC Mon Mar 20 2017
!
version 15.1
service timestamps debug datetime msec
service timestamps log datetime msec
service password-encryption
!
hostname R8
!
boot-start-marker
boot-end-marker
!
enable secret !PASSWORD DELETED!
!
!
!
aaa session-id common
!
!
dot11 syslog
ip source-route
!
!
ip cef
!
!
no ip domain lookup
!
multilink bundle-name authenticated
!
!
!
!
!
!
license udi pid CISCO2811 sn !DELETED!
username Cisco privilege 15 password 7 !PASSWORD DELETED!
!
redundancy
!
!
interface Loopback0
 ip address 1.1.1.8 255.255.255.255
!
interface Loopback101
 ip address 10.101.0.8 255.255.255.0
!
interface FastEthernet0/0
 ip address 192.168.0.8 255.255.255.0
 duplex auto
 speed auto
!
interface FastEthernet0/1
 ip address 192.168.1.250 255.255.255.0
 duplex auto
 speed auto
!
interface Serial0/0/0
 no ip address
 shutdown
 clock rate 2000000
!
router ospf 1
 router-id 1.1.1.8
 log-adjacency-changes
 network 1.1.1.8 0.0.0.0 area 0
 network 10.101.0.0 0.0.0.255 area 0
 network 192.168.0.0 0.0.0.255 area 0
 network 192.168.1.0 0.0.0.255 area 0
!
ip forward-protocol nd
no ip http server
no ip http secure-server
!
!
ip route 0.0.0.0 0.0.0.0 192.168.1.1
!
!
!
!
!
control-plane
!
banner login
*************************************************************************
** This is private network! Unauthorised access is a criminal offense  **
** and violator may be subjec of prosecution.                          **
**                                                                     **
** ROUTER 2811, U-8 2xEth, 1xSERIAL, 1xNM16A Terminal server           **
**                                                                     **
*************************************************************************
!
!         
line con 0
 exec-timeout 5 0
 password 7 !PASSWORD DELETED!
 logging synchronous
 transport preferred none
 transport output all
line aux 0
line 1/0 1/15
 exec-timeout 5 0
 password 7 !PASSWORD DELETED!
 transport input telnet ssh
line vty 0 4
 exec-timeout 5 0
 password 7 !PASSWORD DELETED!
 transport input telnet ssh
line vty 5 15
 exec-timeout 5 0
 password 7 !PASSWORD DELETED!
 transport input telnet ssh
!
scheduler allocate 20000 1000
end

(rest of routers/switches have pretty much same config)

Thanks

Richard Burts · ‎03-20-2017

I am not sure that I am correctly understanding your question. Are you saying that in a previous corporate network that you would have a session on one router and that you would type 192.168.0.1 and that this would result in a telnet session to a router having 192.168.0.1 as its address?

HTH

Rick

HTH

Rick

mungos301 · ‎03-20-2017

Hi, thank you for question

When I like to telnet to router (from another router or switch) I needed type only IP address (without command "telnet" in front), this is normal in corporate network where I used to work.

Now in my private lab when type IP address only, I receive message

R8#192.168.0.12
   ^
% Invalid input detected at '^' marker.

same thing in corporate network work, type IP address and automatically telnet to target router (without "telnet" command). No session open before.

Regards

I suppose there should be something in IOS 15 (most devices in corporate network what I talked was on 12.x)

Tommy

Richard Burts · ‎03-21-2017

Tommy

I am not sure how that was done but my guess is that they used the alias command to create the telnet links. It might look something like this

alias exec 192.168.0.12 telnet 192.168.0.12

HTH

Rick

HTH

Rick

mungos301 · ‎03-21-2017

Hi

thak you for answer, but none of that.

I remember very well how devices were configured, no alias or other similar config.

only difference from my lab is IOS 15 and tacacs. I suppose tacacs should not make difference, and only IOS 15 stay as reason.

I compare configs I have in backup and configs from router in lab. no difference in line* configs or domain name or similar.

However, thank you for answer once again

Tomislav

Richard Burts · ‎03-21-2017

Tomislav

If you are sure that there were no aliases configured then I wonder if they might have used the ip host command to identify the router to which you would telnet.

If you have a copy of a config from the corporate network then perhaps you could post it and we might be able to identify what they were using.

HTH

Rick

HTH

Rick

mungos301 · ‎03-21-2017

Hi

I found something on internet:

http://www.cisco.com/c/en/us/td/docs/ios/termserv/command/reference/tsv_book/tsv_s1.html#wp1069219

scroll down or search "telnet"...

it says:

With the Cisco IOS implementation of TCP/IP, you are not required to enter the connect or telnet command to establish a terminal connection. You can enter only the learned hostname—as long as the following conditions are met:

The hostname is different from a command word for the router.
The preferred transport protocol is set to telnet.

On my routers this not work (as I talk before).

(probably version 15 need first default transport set or similar).

I did not have enough time to study whole page... I hope I'll find time to do that.

Regards

Tomislav

Joseph W. Doherty · ‎03-21-2017

It might be an artifact of the newer IOS versions.

Like you, I commonly telnet from Cisco devices to other devices just keying in the IP. We have few later 15.x systems, and I those that we do have (with an early 15.x), I think, still support it. However, I did notice on the Nexus platforms I support, they require the command line telnet keyword.