[j-nsp] ex-series: etherchannel bpdu loop ?

Alexandre Snarskii snar at snar.spb.ru
Wed Mar 18 13:39:34 EDT 2009


After power failure on one of our pop's we faced strange problem: 
etherchannel between juniper ex-4200 and cisco 2960g started to 
flap. By logs I saw that Cisco determined 'etherchannel 
misconfiguration' condition, shuts down both ports of channel,
then, after errdisable timeout, tried to set them up, but then 
again detects etherchannel misconfiguration and so on and on... 

By Cisco documentation, etherchannel misconfiguration means 
that BPDU's sent on one ports of etherchannel returned back 
via another port. And forwarding of those BPDU from one
LAG member interface to another (rstp is disabled on juniper)
smells like an error in JunOS... 

Workaround: delete interfaces from LAG on Juniper, commit,
add interfaces to LAG, commit. 

PS: Configuration is pretty straightforward on both sides: 


snar at SW006-201> show configuration interfaces ae0 
aggregated-ether-options {
    minimum-links 1;
    link-speed 1g;
unit 0 {
    family ethernet-switching {
        port-mode trunk;
        vlan {
            members all;
snar at SW006-201> show configuration interfaces ge-0/0/15    
ether-options {
    speed {
    802.3ad ae0;
snar at SW006-201> show configuration protocols    
stp {
rstp {
mstp {


Cisco#show runn int po1
interface Port-channel1
 switchport mode trunk
 mvr type source
Cisco#show runn int gi 0/23
interface GigabitEthernet0/23
 switchport mode trunk
 load-interval 30
 channel-group 1 mode on

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