RE: BGP flapping

From: Brian Dennis (bdennis@internetworkexpert.com)
Date: Tue Jun 22 2004 - 00:55:25 GMT-3


Do a "debug ppp negotiation" and you will see that actually the
interface is bouncing which is causing the BGP session to reset. Some
IOS versions have keepalives enabled by default on the virtual-template
interface. Try enabling or disabling, whichever the case maybe,
keepalives on the virtual-template interface.

Before disabling keepalives:

BB1#sho int virtual-access 11
Virtual-Access12 is up, line protocol is up
  Hardware is Virtual Access interface
  Internet address is 54.1.8.254/24
  MTU 1500 bytes, BW 100000 Kbit, DLY 100000 usec,
     reliability 255/255, txload 1/255, rxload 1/255
  Encapsulation PPP, loopback not set
  Keepalive set (10 sec) <----
 <snip>
BB1#

After disabling keepalives:

BB1#sho int virtual-access 11
Virtual-Access12 is up, line protocol is up
  Hardware is Virtual Access interface
  Internet address is 54.1.8.254/24
  MTU 1500 bytes, BW 100000 Kbit, DLY 100000 usec,
     reliability 255/255, txload 1/255, rxload 1/255
  Encapsulation PPP, loopback not set
  Keepalive not set <----
 <snip>
BB1#

Brian Dennis, CCIE #2210 (R&S/ISP-Dial/Security)
bdennis@internetworkexpert.com
Internetwork Expert, Inc.
http://www.InternetworkExpert.com
Toll Free: 877-224-8987
Direct: 775-745-6404 (Outside the US and Canada)

-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
ccie2be
Sent: Monday, June 21, 2004 8:41 PM
To: Group Study
Subject: BGP flapping

Hi Guys,

This has been bothering me most of today. I just can't figure it out.

I'm doing a practice lab and R6 has 2 pppoATm connections to BB1. The
configs
are shown below.

Aside from BGP, there aren't any other routing protocols running between
R6
and BB1.

I tried using ( and not using) nei... ebgp multihop and the same for
nei ...
update-source lo0.

Nothing seems to make any difference. The BGP session just keeps
flapping up
and down.

Anyone know what's going on here? If so, please tell me what I should
do to
correct this annoying problem.

Thanks kindly, Tim

interface ATM1/0
 no ip address
 no atm ilmi-keepalive
 pvc 0/16 ilmi
 !
!
interface ATM1/0.206 point-to-point
 pvc 0/206
 --More--
11:50:11: %BGP-5-ADJCHANGE: neighbor 54.6.8.254 Down Peer closed the
session
  broadcast
  encapsulation aal5snap
  protocol ppp Virtual-Template1
 !
!
interface ATM1/0.306 point-to-point
 pvc 0/306
  encapsulation aal5snap
  protocol ppp dialer
  dialer pool-member 1
 !

router bgp 100
 no synchronization
 bgp log-neighbor-changes
 network 142.6.40.0 mask 255.255.248.0
 neighbor 54.6.7.254 remote-as 54
 neighbor 54.6.7.254 ebgp-multihop 255
 neighbor 54.6.7.254 update-source Loopback0
 neighbor 54.6.8.254 remote-as 54
 neighbor 142.6.46.4 remote-as 45
 neighbor 204.12.6.3 remote-as 200
 neighbor 204.12.6.254 remote-as 54
 no auto-summary

 --More--
11:51:34: %BGP-5-ADJCHANGE: neighbor 54.6.7.254 Up
 --More--
11:51:46: %BGP-5-ADJCHANGE: neighbor 54.6.8.254 Up
 --More--



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