MTU size

What is the hardware device type and model.

Some routers/L3 switches have MTU set at the "system" level and all interfaces use that as the default MTU.

In this case, hw is Cisco7204 VXR.... how does one find the defualt MTU Val set @ the system level??

I have not worked with MPLS networks  before, but I would also check with your MPLS provider.  I would assume with the MPLS tagging that your MTU would need to be bigger than 1500.

Just editing my reply because just forgot the pop function. The SP, before sending the MPLS frame back to customer strips off any MPLS tagging and hence the frame arrives(should arrive)  at 1500 bytes only.

4470 is the max supported size of the port adapter. There will be no fragmentation till that size. So although it's showing 4470, I am sure it's receiving MTU much lesser size than that.

Does not look like you will have an MTU issue here.

Best,

Assuming that you are end point/last hop on the MPLS network, yes the MPLS tags are remove.

However, if you are a middle point routing you would still see them.

I would run a packet capture on the serial  interface and see what you are receiving.

Although I would not expect to see CRC errors because of a MTU mismatch.

Giltjr;
None of the above command work.. sh system or sh jumbo...

Is there a way to display what MTU size is received from service provider assuming it is being tagged?

I agree with Giltjr  that MTU size won't give you interface errors. If interface errors are the one we are looking for, something else is there.  Packet capture can tell you the mtu size. I don't recall anything in router that shows mtu size of received packets.....

Best,

Yes, we are looking to find the source of errors on input.. could it be framing from the provider??

It seems to be physical in nature. Probably one or more T1's are generating errors.

First test to be done is Hard plug loopback tests  to clear the router and the t3 port adapter of fault.

input errors typically are never alone. There will be other accompanying errors like crc or drops. Please clear the counters and post the "sh int serialXX"  output. If too many error counters are there in 1 hr, you should ask your SP to do a intrusive testing so that they can see those errors.

They can test individual T1's with BERT. If you are comfortable enough, you can yourself do loop testing on every T1 to determine which one is faulty.

Best,

Does framing play any role in input error.. right now it is M23 for DS3 connection and think it is not right..

I wouldn't expect it to.  If you do have a framing issue though there should be an LOF alarm on the physical interface if you look at the router.

But again, that usually comes back to a physical issue such as a bad cable, or the framing type is incorrect.

Was it working at all?  I would expect it not to work at all if the framing was set incorrectly and changing MTU would not cause it to get better.