Help with Rip v2 lab

Unanswered Question
Nov 28th, 2008


In my lab I have got 3 routers which I have connected to each other using their serial cables.

I'm using DTE/DCE back-to-back cables.

Anyway all is working fine, but the serial links are so slow, what speed are they and do I need to configure their speed?

The reason I ask is it took 10 minutes to copy a 11mb from one router LAN to another routers LAN?


I have this problem too.
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Giuseppe Larosa Fri, 11/28/2008 - 14:04

Hello Andy,

how fast you can go depends on your hardware: if you are using A/S serial interfaces they cannot reach 2 Mbps but probably not more then 128000 bps in sync mode.

to see the real speed you can:

check the clock rate command on the DCE side


sh controller serx/y check the TX or RX clock rate.

for the hardware you can verify using

show ver

show hardw

These interfaces can be slow but allow you to test different features like FR, FR switching, PPP encapsulation and so on

Hope to help


whiteford Sat, 11/29/2008 - 00:05

Thanks for finding the time to help me.

1.) On my DCE sides I have the clock rate set at 128000, what is this rate? I only used this rate from an example, can I increase this?

2.) Are serial connections used a lot today?

3.) A/S serial?

4.) My next task is upgrading to ospf

Many thanks I have attached a diag and one of the configs.

Giuseppe Larosa Sat, 11/29/2008 - 02:29

Hello Andy,

if you have only two serial interfaces they are synchronous and you can increase the clock rate up to 2048000 I think.

just type clock rate ? and see the suggested values.

Your serial interfaces are running at 128 kbps that is quite slow nowdays.

In synchronous serial interfaces the clock rate is also the speed of the link.

2) They are still used, for example in combination with HDSL. They offer symmetric speed while ADSL doesn't. The advent of broadband access xDSL, cable modems has changed the WAN landscape

3) there are modules with 8 ports that behave in two ways: as sync as the ports you already have or as async lines that can be used to build a terminal server: if you have 8 serials in the same module for sure they are A/S.

the sh ver can tell you what you have.

But if I remember correctly from other thread when we discussed about the cables for back-to-back connections you have the normal sync serials on your routers.

4) you can work with OSPF in your lab even at 128 kbps.

Hope to help


whiteford Sun, 11/30/2008 - 02:28

Thanks fo you help.

1.) What is the differce betweek clock rate and bandwidth?

2.) If the bandwidth is lower on one route will it use the faster router?

3.) Just one more thing. I'm not if you have looked at me network diagram, but I have loopbacks to allow me to ping and test RIP, but what if 2 loopbacks or LAN's are using the same IP range. I know a good way round this which I've seen engineers do is NAT, as the LAN's are too big to change.

Is this something I could achieve with my setup?


Giuseppe Larosa Sun, 11/30/2008 - 04:43

Hello Andy,

1) the clock rate is the real speed of the link, bandwidth is an administrative parameter that can be changed indipendently of real link speed

int ser0/0

bandwidth 128

! this makes the BW 128 kbps

Changing BW has effects on dynamic routing if using OSPF or EIGRP and on the modular QoS.

2) with OSPF yes, with RIP no

3) you can also test NAT with your setup. remember that you can multiply the LAN interfaces using subinterfaces

But I would suggest you to do it later: before take confidence with OSPF and then focus on NAT.

Hope to help


whiteford Sun, 11/30/2008 - 04:52

Thanks so if you use OSPF and BW on the interfaces it can be configured to take the fastest link?

I'm doing my ICND1 and ICND 2 studies, I will upgrade to OSPF next although my instructure said it's complicated to set up, at the moment all I know is you set up "areas" on each of my 3 routers, and that like Rip v2 it is classless.

whiteford Sun, 11/30/2008 - 13:45

Just to let you know I ran clock rate and the interfaces said 300-800000, so I set them all to 800000.

thotsaphon Sun, 11/30/2008 - 04:52

hi Andy,

Clock rate is what you're thinking about access-rate. Let's say I want to use 512k bandwidth of link. It means that the router can send packets at that rate.

A "bandwidth" command is to reference bandwidth on the interface. The router will use this bandwidtd to calculate what it wants. f.e. Path cost , Metric or something.

Actually you should configure the bandwidth to be the same value of the real clock that you're using.

Note : DTE/DCE In your case you have to provide clock on one side. It's DCE side.


whiteford Sun, 11/30/2008 - 04:58

Thanks, does the bandwidth have to be configured on the DCE router and DTE router, both side of the route I mean?

thotsaphon Sun, 11/30/2008 - 05:04


You're using DTE/DCE back-to-back. You have to configure on one side to provide clock. It's DCE.

Just think when you're connecting the router to ISP's modem. Who's providing clock to you? ISP right? Which type of cable you are using on the router. DTE right?


whiteford Sun, 11/30/2008 - 05:08

Thanks, I'm clear on the DCE clock side does the bandwith setting only get put on the DTE side with the clock rate?

thotsaphon Sun, 11/30/2008 - 05:14


There are two things.

1. Clock Rate , You have to configure on DCE side.

2. A bandwidth command. Technically speaking, you should configure the same value on both sides to tell routers how much bandwidth they are using. If they are runing RIP then they can calculate the correct value on both side.




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