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New Member

Need help understanding clocking


For the most part I understand the purpose of clocking. The majority of our circuits are Sprint MPLS and the clocking is derived from the line.

What I'm confused about is how to configure clocking on a pair of routers that are connected to each other via point to point T1's as well as other networks that provide clocking.

For this new setup I have the following

2 Cisco 2801 Routers

Router A has

- One VWIC2-2MFT-T1/E1 card (connected to Router B)

- One WIC-1DSU-T1-V2 Card (connected to Sprint MPLS)

Router B has

- One VWIC2-2MFT-T1/E1 card (Connected to Router A)

- One ADSL card (Connected to Covad)

Router A's WIC-1DSU-T1-V2 is connected to a Sprint MPLS T1 with clocking coming from the line.

Router A's VWIC2-2MFT-T1/E1 is connected to Router B's VWIC2-2MFT-T1/E1 via a pair of Point to Point T1's configured in a multilink bundle.

On the Point to Points Qwest said one of my devices needs to provide clocking to the other, so on Router B on Controller T1 0/2/0 and 0/2/1 I set "clock source internal"

I am seeing slips on both serial interfaces and am a little unsure as to why.

From the reading I've done on the Cisco site it seems to indicate a router can only have one clocking source for all interfaces, so I'm lost.

Thank you,



Re: Need help understanding clocking

Have you tried setting both controllers to internal clock source?

All of my circuits go through 2 separate providers, and I have them all configured for "clock source internal". If we have frame slips and such, we verify the clock source, do some basic troubleshooting then have the carrier test the line.

We have also had situations where a poorly grounded UPS was causing frame slips to a T1 circuit that was within 6 inches of the UPS. So interference could also be an issue.


New Member

Re: Need help understanding clocking

I gave it a shot and the slips were worse.

After trying several different configurations I finally got it.

For the one router attached to both Sprint and the Point to Points

The single port WIC card is configured for clock source line (Sprint MPLS Circuit)

Both Controllers are now configured clock source internal

And Clock-Source-Participate WIC 0 is set

For the router connected to the Point to Point's and ADSL

I configured the Controllers with clock source line and NO clock-source-participate WIC 2

The key was the No Clock-Source-Participate WIC 2

Now I need to read up on that setting.