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3 vWICs in 2821 = errors? (I'm at a loss.)

I learned yesterday that Cisco only truly supports 4 T1s in a 2821. I have 3 WICs in a 2821 (6 T1s) and it's been "working" fine. I noticed that I've been incurring CRC errors on ALL 6 of my interfaces. I've contacted the local telco, and they tested their line clean. I then had them come out and test from demarc to them, and it tested clean.

All of the connections are individual frame links that are bundled on my end. My question is:

If Cisco only supports 4 T1s coming into the router, and I have 6, will I a.) get CRC errors (normally line issue) and b.) will I see them only on the cards that's having a problem or will it be just local to the card that's having a problem.

Thanks,

John

HTH, John *** Please rate all useful posts ***
7 REPLIES
Hall of Fame Super Gold

Re: 3 vWICs in 2821 = errors? (I'm at a loss.)

There is no limitation to the number of cards supported, your issue have a different cause.

Re: 3 vWICs in 2821 = errors? (I'm at a loss.)

The problem is fixed, and I'm posting here so everyone will know how I fixed it.

The telco tested everything fine, and it showed that the router was causing the errors. The problem is this:

When multiple vWICs are all set to network clock participate, they are all pulling the clock from the line. Since they were ALL doing this, it seemed that they were fighting because they were all also pulling from the backplane to get the timing.

I made one controller the primary, and then I set the other controllers to pull the clocking from that one and all of my errors went away.

controller t1 0/0/0

clock source line primary

controller t1 0/0/1

clock source line

controller t1 0/1/0

clock source line

controller t1 0/1/1

clock source line

network-clock-participate wic 0

network-clock-participate wic 1

network-clock-participate wic 2

network-clock-select 1 t1 0/0/0

The "network-clock-select" tells all of the other cards to get their clocking from t1 0/0/0. All of my errors went away and it resolved my issue.

HTH in the future,

John

HTH, John *** Please rate all useful posts ***
Hall of Fame Super Bronze

Re: 3 vWICs in 2821 = errors? (I'm at a loss.)

Good info, rated.

Community Member

Re: 3 vWICs in 2821 = errors? (I'm at a loss.)

All these years later.....still works like a charm!

VIP Purple

Re: 3 vWICs in 2821 = errors? (I'm at a loss.)

Hello John

cheers for this - great 5* information 

res

paul

Please don't forget to rate any posts that have been helpful. Thanks.
Community Member

Re: 3 vWICs in 2821 = errors? (I'm at a loss.)

Hi John,

After 6 hours of searching all the internet, trying to configure clock source independent, reconfiguring the mgcp gateway, i have finally found the solution here.This command "network-clock-select" should be written all over the web sites, even included by Cisco in their official documentation(because i didn't found it anywhere included).

Thank you,

George.

Hall of Fame Super Gold

Re: 3 vWICs in 2821 = errors? (I'm at a loss.)

That is actually a subject that any reputable consultant, or certified Cisco partnerr, normally configure all the time.

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