Difference between T3 going down and Layer3 down.

[SACHIN SHARMA]

When we asked service provider to do intrusive test on the circuit due to BGP neighbor bounce they have asked this question

They want to know whether T3 link itself went down or BGP layer3 drop has occured.Can anyone explain?

Thnx in advance...

[gerald.suiza · Accepted solution]

BGP can drop even if the physical interface does no go down (T3 interface is down/down or protool down). In these cases it could be that errors are so excessive that the BGP keep alives do not reach the BGP neighbor and cause BGP to drop or there are times that the link is so utilized that it starves out BGP and BGP adjacency drops.

So if the servce provider wants to know if the physical interface went hard down or if ONLY BGP dropped so they have a clearer picture of the issue and so that they know where to start looking for the problem.

HTH

[SACHIN SHARMA]

How to identify whether it is a physical layer drop or only bgp drop.i cannot find any info from "sh log" command.can you give me the trouble-shooting commands to identify the issue.

thnx in advance...

[gerald.suiza]

try and see if you have interface resets when you do a sh interface. also i would look for crc's and i would look at the the controller. what kind of serial interface do you have?

[SACHIN SHARMA]

It is T3

Serial2/0 is up, line protocol is up

  Hardware is M1T-T3+ pa

   Internet address is xx.xx.xx.xx/30

  MTU 1500 bytes, BW 44210 Kbit/sec, DLY 200 usec,

     reliability 255/255, txload 1/255, rxload 1/255

  Encapsulation PPP, LCP Open

  Open: IPCP, crc 16, loopback not set

  Keepalive set (10 sec)

  Restart-Delay is 0 secs

  Last input 00:00:00, output 00:00:00, output hang never

  Last clearing of "show interface" counters 1d12h

  Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 0

  Queueing strategy: Class-based queueing

  Output queue: 0/1000/64/0 (size/max total/threshold/drops)

     Conversations  0/87/256 (active/max active/max total)

     Reserved Conversations 2/2 (allocated/max allocated)

     Available Bandwidth 29621 kilobits/sec

  30 second input rate 0 bits/sec, 0 packets/sec

  30 second output rate 3000 bits/sec, 1 packets/sec

     76408 packets input, 4655533 bytes, 0 no buffer

     Received 0 broadcasts, 0 runts, 0 giants, 0 throttles

              0 parity

     0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored, 0 abort

     146573 packets output, 26435253 bytes, 0 underruns

     0 output errors, 0 applique, 0 interface resets

     0 unknown protocol drops

     0 output buffer failures, 0 output buffers swapped out

     0 carrier transitions

   rxLOS inactive, rxLOF inactive, rxAIS inactive

   txAIS inactive, rxRAI inactive, txRAI inactive