BGP default goes disappeared sometime

Unanswered Question
Oct 14th, 2007

This is an ADSL atm network using a 2811 router.

My atm port is, edge router is

1. Every once a while the B* [20/0] via, 6d20h default route would go disappeared, so BGP would change to Active.

2. show inteface bri said, atm 0/0 was up/up

3. I connected to the router through the back door, found out, the atm 0/0 port is not pingable.

4. To resolve the issue, I would need a shut/no shut on the atm 0/0, BGP would be reestablish, and it would work for 5-15 days.

Here is my normal routing table

C is directly connected, FastEthernet0/0

C is directly connected, Loopback0

C is directly connected, ATM0/0/0

B [200/0] via, 6d20h, Null0

C is directly connected, GigabitEthernet1/0

B* [20/0] via, 6d20h

=====show log when default route disappear==

Oct 6 11:01:36.330 CDT: %PIM-5-DRCHG: DR change from neighbor to 10.152

.254.2 on interface ATM0/0/0

Oct 6 11:01:45.219 CDT: %LINK-3-UPDOWN: Interface ATM0/0/0, changed state to do


Oct 6 11:01:46.219 CDT: %LINEPROTO-5-UPDOWN: Line protocol on Interface ATM0/0/

0, changed state to down

Oct 6 11:02:05.223 CDT: %LINK-3-UPDOWN: Interface ATM0/0/0, changed state to up

Oct 6 11:02:06.223 CDT: %LINEPROTO-5-UPDOWN: Line protocol on Interface ATM0/0/

0, changed state to up

Oct 6 11:02:06.351 CDT: %PIM-5-DRCHG: DR change from neighbor to 10.15

.254.2 on interface ATM0/0/0

Oct 6 11:02:07.919 CDT: %PIM-5-NBRCHG: neighbor UP on interface AT


Oct 6 11:03:52.922 CDT: %PIM-5-NBRCHG: neighbor DOWN on interface

ATM0/0/0 non DR


ATM0/0/0 is up, line protocol is up

Hardware is HWIC-DSLSAR (with Alcatel ADSL Module)

Internet address is

MTU 4470 bytes, sub MTU 4470, BW 512 Kbit, DLY 1000 usec,

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

Encapsulation ATM, loopback not set

Encapsulation(s): AAL5 AAL2, PVC mode

23 maximum active VCs, 256 VCs per VP, 1 current VCCs

VC Auto Creation Disabled.

VC idle disconnect time: 300 seconds

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

Last clearing of "show interface" counters 6d07h

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

Queueing strategy: Per VC Queueing

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

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

984032 packets input, 500586163 bytes, 0 no buffer

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

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

838225 packets output, 106313349 bytes, 0 underruns

0 output errors, 0 collisions, 0 interface resets

0 output buffer failures, 0 output buffers swapped out


There are several hundred routers having the same problem lately which connected different ISP.

I think there are 3 ways to drop default route route

A. My NIC has problem.

B. The DSLAM has problem on

C. IOS has changed about 8 weeks ago. I am using Version 12.4(13r)T

D. I am planning to add a static route with AD = 21, hopefully, the static would connect to ISP, when default is gone.

Anyother suggestion?

I have this problem too.
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jsivulka Fri, 10/19/2007 - 07:03

What you can see is that, during the failure, the has disappeared from the 'sh ip bgp'!! This shouldn't be possible, because you are learning teh default from a eirgp neighbor. The entry in the routing table hasn't been flushed for hours!!


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