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Cisco PortChannel - Traffic only going through after delete and add back vlan

Kumaran83
Level 1
Level 1

Hi,

 

I have an strange issue affected my network last night. Few equipment were down which belongs to same vlan. Only ping is going thru but not any other traffic. I cant even login thru web to these monitoring servers.

 

Network setup as follow:

Core switch <-->Access Switch <-->Servers

 

Core Switch:

IPCORE-C6506E-CORERTR#sh ver
Cisco IOS Software, s2t54 Software (s2t54-ADVENTERPRISEK9-M), Version 15.0(1)SY6, RELEASE SOFTWARE (fc4)
Technical Support: http://www.cisco.com/techsupport
Copyright (c) 1986-2014 by Cisco Systems, Inc.
Compiled Sat 01-Feb-14 04:46 by prod_rel_team

ROM: System Bootstrap, Version 12.2(50r)SYS3, RELEASE SOFTWARE (fc1)

 

Access Switch:

Cisco IOS Software, C3750E Software (C3750E-UNIVERSALK9-M), Version 15.0(2)SE6, RELEASE SOFTWARE (fc2)
Technical Support: http://www.cisco.com/techsupport
Copyright (c) 1986-2014 by Cisco Systems, Inc.
Compiled Wed 09-Apr-14 02:55 by prod_rel_team

ROM: Bootstrap program is C3750E boot loader
BOOTLDR: C3750E Boot Loader (C3750X-HBOOT-M) Version 12.2(58r)SE1, RELEASE SOFTWARE (fc1)

 

 

There are 2 trunk interfaces configured under Port channel between switches:

 

interface Port-channel1
description *** Connection to IPCORE-C6506E-CORERTR ***
switchport trunk encapsulation dot1q
switchport trunk allowed vlan 5,8,11,12,14,16,20

 

Group Port-channel Protocol Ports
------+-------------+-----------+-----------------------------------------------
1 Po1(SU) LACP Te1/1/1(P) Te1/1/2(P)

IPCORE-C3750X-ServSW#

 

There is no log found on cisco core switch or access switch during the incident or any changes to network.

Connection(PING) is stable to all servers during the incident, so i dont think the SFP module/cabling has issue. 

 

Connection to servers back to normal after i removed the affected vlan(16) and add back to port channel.

 

Looks like issue more to layer 2 related.

 

Since there is no any log i couldn't figure out what went wrong. I believe this may happen again and need to find permanent solution for this.  

 

Expert please advice. 

 

regards.

 

 

 

2 Replies 2

Hello,

 

you might want to check which of your switches is the root for your Vlans. Ideally it would be the core switch. On the core switch, for each vlan, issue the command:

 

show spanning-tree vlan x

 

The output shoud show something like the line in bold:

 

Switch#sh spanning-tree vlan 2

VLAN0002
Spanning tree enabled protocol rstp
Root ID Priority 32769
Address 527c.6030.b600
This bridge is the root
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec

Hi Georg,

 

I notice actually there are 2 vlans been affected by this trunk. 1 of is vlan 7. Many devices been affected by this vlan. 

 

It used to be root bridge at core swicth:

IPCORE-C6506E-CORERTR#sh sp vlan 7

VLAN0007
Spanning tree enabled protocol rstp
Root ID Priority 24583
Address 0008.e3ff.fd90
This bridge is the root
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec

Bridge ID Priority 24583 (priority 24576 sys-id-ext 7)
Address 0008.e3ff.fd90
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Aging Time 480

Interface Role Sts Cost Prio.Nbr Type
------------------- ---- --- --------- -------- --------------------------------
Gi1/1/45 Desg FWD 4 128.2093 P2p
Gi2/1/45 Desg FWD 4 128.4141 P2p Peer(STP)
Po8 Desg FWD 1 128.5772 P2p Peer(STP)

 

But after add vlan 7 into another portchannel it wasnt elected as root bridge:

IPCORE-C6506E-CORERTR#sh sp vlan 7

VLAN0007
Spanning tree enabled protocol rstp
Root ID Priority 0
Address 3462.886e.7d3d
Cost 20001
Port 5762 (Port-channel2)
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec

Bridge ID Priority 24583 (priority 24576 sys-id-ext 7)
Address 0008.e3ff.fd90
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Aging Time 480

Interface Role Sts Cost Prio.Nbr Type
------------------- ---- --- --------- -------- --------------------------------
Gi1/1/45 Desg FWD 4 128.2093 P2p
Gi2/1/45 Desg FWD 4 128.4141 P2p Peer(STP)
Po2 Root FWD 1 128.5762 P2p Peer(STP)
Po8 Desg FWD 1 128.5772 P2p Peer(STP)

IPCORE-C6506E-CORERTR#

 

 

May I know why vlan in trunk need to remove and add back to restore all traffic? Is it related to root bridge? Any workaround to solve this issue?

 

Thanks.

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