Encapsulation

A common problem which I have seen during point to point circuit testing is an Encapsulation problem. If you work in an organization where you don’t have a control on the other side then you know what I am talking about.

I have seen that if you are backbone guy and you are setting your router interface to encapsulation ppp. You will somehow tend to assume that engineer on the other side is also using ppp encapsulation. In most of the cases this assumption always leads to wastage of time in circuit testing.

By default on all cisco interfaces, encapsulation is HDLC ( cisco proprietary) . During testing of new point to point links, always try to verify encapsulation at both ends, if on one side you have hdlc and on other side you have ppp, then your link will never come up.

If you don’t have a control on the other side of the link then either try to configure encapsulation ppp at your side or if you have already configured ppp on your side, try removing it.

Router1(config)# interface serial 0
Router1(config-if)#encapsulation ppp

or

Router1(config)#interface serial 0
Router1(config-if) no encapsulation ppp

Changing encapsulation always work.

Reload Command

Last night I was doing an IOS upgrade remotely for one of our remote office. After upgrade I had to apply some ACL’s for QOS. As soon as I applied the ACL I lost the connection. And I was not able to log in to the router after that.

Guess what, I was able to access the router after 10 minutes. How is this possible?

I think some of you must have already guessed it! J. Yeah! Whenever I do any configuration changes remotely, I always issue reload in 15 command. This will reload the router after 15 minutes. But a warning here, If your configuration is successful, try to save your configuration before 15 minutes. Otherwise you will loose your successful configuration also.

Conclusion:-Every time you try to do remote configuration changes, you should try to use reload in x (where x is minutes) command at the start. It will reload your router after x minutes in case you loose your remote telnet connection. If you make a mistake and can no longer get to the router because of the change you made, you have to make the embarrassing call to someone to go “hit the power.” The power cycle takes the router back to the original starting configuration because your change was never saved. Using this command can save you from making embarrassing call.

Mistyped Commands

Whenever we mistype something on our router prompt, it’s frustrating to see router taking a long time before coming back to the prompt. 

Sikandar#shwo
Translating "shwo"…domain server (192.168.37.23)
% Unknown command or computer name, or unable to find computer address
Sikandar#

Just with a small mistype, router assumes that we are trying to telnet to the device shwo . To avoid this, we can use a line command transport preferred none.  
! Console port
line con 0
transport preferred none
! VTY Ports
line vty 0 5
transport preferred none

Now see the difference, here it will not try to telnet to the device.Router already knows that this is a mistype rather then any device which we are trying to telnet.

Sikandar#shwo
^
% Invalid input detected at '^' marker.