Relyl on a serial interface

Hey guys quick question.

Is low reliability an indication of a physical layer issue? I am working on a t1 which rely keeps going up and down. I have seen it bounce between 195 and 238 over 255.

Find more posts tagged with

Save $250 on 2025 certification boot camps from Infosec!

Book now with code EOY2025

Button

Comments

gojericho0

This could be caused by numerous things at either level. When it bounces, does both the line protocol and link go down?

Can you display a sh int?

Have the other circuits in the path been tested? If so are they having any issues or do they come up clean?

gaby_978

Log doesnt show any bounces. The last time it bouce was back in may 5th. The ckt shows up/up with rely going up and down. and I also see input errors. We are getting crc and aborts.

gojericho0

what type of circuit is it? Usually if its a WAN circuit CRC errors are caused by bad cable pair. If its ethernet it may be a duplex mismatch

gojericho0

Also do you see carrier transitions on your side? can you post the sh int stats on both your side and the other end?

shednik

Does the T1 have an external CSU/DSU or is it internal to the T1 card?

If external are there any errors on the CSU?

Are the CRC and input errors still climbing?

Has a clear counters been done recently to see if they come back?

gaby_978

After doing some testin with one of the engineers here we came with the conclusion that the port where that t1 is riding is bad. We can't even see the serial looped when looping the local port. This is a PE router for an ISP. I try to loop another t1 on the same t3 controller and was able to see the loop. Sorry I couldnt port sh int but this for a customer connection...