Quick Help on serial connections

[dave]

I am taking my CCNA in a couple days, and the only issue I have with the exam is the following:

They ask you to establish a serial connection between to labs (Router A and B), and be able to ping one router from the other. Set the clock rate on the DCE side, enable the interfaces (S0, S1), and set the encaps type were all that I thought you needed to dpo.. but apparently not. Also, the simulator on the exam doesnt allow you to set an encapsulation type. Quick responses would be greatly appreciated, thanks.

Dave Robinson

[donewald · Accepted solution]

Dave,

You did not mention putting ip's on the interfaces but assume you are doing that. Encap by default is cisco HDLC so if both routers are default you should not need to do this. Setting the clock rate(DCE), no shutting the interfaces, and IP assignment should be all that is required for Router a to B ping.

Hope this helps,

Don

[dave]

Don:

I appreciate the response, but thats exactly what I did. The ask you to use the 192.168.128.0 networking scheme.. so I assigned one of the serial ports to 192.168.128.1 and the other to 192.168.128.2. The exact topology is as follows:

Lab_B (Router B) is connected to a switch, which has two hosts connected to it. You use on of these hosts to configure the router, and there are options to configure the host (Ip address, default gateway).

Lab_B is connected to Lab_C via a serial connection, Lab_B is the DCE side. The same setup (Switch, two hosts) is on the other lab.

I am definitely confused as to why it's not working.. I set the clock rate to 56000, do i need to set the bandwidth?

Dave

[kholford]

In regards to the bandwidth... I always thought the bandwidth statement was just an informational line in the configuration but a Cisco Engineer told me that it does more and that it is important to specify the bandwidth.

[scottmac]

My understanding of the Bandwidth parameter is that the value associated with that parameter is used in the calculation of some routing metrics.

It has no effect on the actual interface operation, just in path determination of some routing protocols.

FWIW

Scott

[7rbowenii]

All,

The bandwidth statement does in fact change the amount of traffic allowed between the devices. It must be the same on both sides. The simulator (CCNA) I use does want this set. I have used the bandwidth statement to test application characteristics over smaller pipelines...

-Bo

[andyirving]

Have you verified that you have configured the correct end of the link with the clock rate command. Do a "show controllers serial" you should see interface type as DTE or DCE. The clock needs to be on the DCE end. The bandwidth statement has no effect on the amount of traffic put to the interface, it is used for routing protocol metrics. The bandwidth doesn't have to the same on both sides or even configured.

[nicolaswatson]

I disagree with the comments about the bandwidth statement required to be the same at both ends - unless this is simulator dependant. In practice, it makes no difference with basic configs. It is used to calculate routing metrics and as the 100% (255) reference for interface loading. A GOOD practice is to make them the same!

The CCNA exam may require you to be excessive in command input, ie: you may need bandwidth entered, encapsulation, no shut. I did the older CCNA exam format, so could not provide further input on this. In a CCNA prac exam I did, you would fail if you did not put in all of the above, as you are expected to know about all these commands in the CCNA.

Good Luck.