01-23-2014 05:51 AM - edited 03-07-2019 05:44 PM
Hi all, have a quick question on etherchannel, trunking and spanning tree behavior. In packet tracert I've setup 2 physical interfaces as etherchannel "po1" on each side of my switches. I then configured po1 on each side to be a trunk. This is working fine and if I shutdown a single port, the link stays active and I can still forward traffic. Perfect so far!
However, when I do a "no shut" on the downed interface, the entire etherchannel goes through a Spanning Tree initialization and takes the entire etherchannel down for approximately 30 seconds. Is this expected behavior? I thought that Spanning Tree treated the Port Channel as a single entity and as long as one physical interface were up on each side, there would be no reason for spanning tree to renegotiate?
01-23-2014 06:33 AM
When a port is added to a bundle, it needs to check for consistency.
Please read to this document for its behavior
http://www.cisco.com/en/US/tech/tk389/tk213/technologies_tech_note09186a008009448d.shtml
Regards,
01-23-2014 06:39 AM
Hello
You are correct STP treats this as one instance, and the issue you have stated shouldn't really occur, can you post your L2 etherchannel config,
Also
sh spanning-tree interface port-channel x
sh etherchannel port-channel
res
Paul
Please don't forget to rate any posts that have been helpful.
Thanks.
01-23-2014 12:12 PM
Edison, thanks for the link... will read in a few.
pdriver, keep in mind that I'm doing this in packet tracer for proof of concept before I try it in production so maybe it's a quirk with packet tracer? Config is really bare bones >
SW1
!
spanning-tree mode pvst
!
interface FastEthernet0/1
switchport access vlan 3
switchport mode access
!
interface FastEthernet0/2
switchport access vlan 3
switchport mode access
!
interface FastEthernet0/3
switchport access vlan 3
switchport mode access
!
interface FastEthernet0/4
switchport access vlan 96
switchport mode access
!
interface FastEthernet0/5
switchport access vlan 96
switchport mode access
!
interface FastEthernet0/6
switchport access vlan 96
switchport mode access
!
interface FastEthernet0/7
switchport access vlan 13
switchport mode access
!
interface FastEthernet0/8
switchport access vlan 13
switchport mode access
!
interface FastEthernet0/9
switchport access vlan 13
switchport mode access
!
!
interface GigabitEthernet0/1
channel-group 1 mode on
switchport mode trunk
!
interface GigabitEthernet0/2
channel-group 1 mode on
switchport mode trunk
!
interface Port-channel 1
switchport trunk encapsulation dot1q
switchport mode trunk
!
interface Vlan1
no ip address
shutdown
!
interface Vlan3
description 10.3.0.0
ip address 10.3.0.1 255.255.255.0
!
interface Vlan13
description 10.10.13.0
ip address 10.10.13.1 255.255.255.0
!
interface Vlan96
description 10.10.96.0
ip address 10.10.96.1 255.255.255.0
!
ip classless
!
SW2
spanning-tree mode pvst
!
!
interface FastEthernet0/1
switchport access vlan 3
switchport mode access
!
interface FastEthernet0/2
switchport access vlan 3
switchport mode access
!
interface FastEthernet0/3
switchport access vlan 3
switchport mode access
!
interface FastEthernet0/4
switchport access vlan 96
switchport mode access
!
interface FastEthernet0/5
switchport access vlan 96
switchport mode access
!
interface FastEthernet0/6
switchport access vlan 96
switchport mode access
!
interface FastEthernet0/7
switchport access vlan 13
switchport mode access
!
interface FastEthernet0/8
switchport access vlan 13
switchport mode access
!
interface FastEthernet0/9
switchport access vlan 13
switchport mode access
!
!
interface GigabitEthernet0/1
channel-group 1 mode on
switchport mode trunk
!
interface GigabitEthernet0/2
channel-group 1 mode on
switchport mode trunk
!
interface Port-channel 1
switchport trunk encapsulation dot1q
switchport mode trunk
!
interface Vlan1
no ip address
shutdown
!
ip classless
!
!
-------------------------------------------------------------------------------------------------------------
SW1
Switch#sh etherchannel port-channel
Channel-group listing:
----------------------
Group: 1
----------
Port-channels in the group:
---------------------------
Port-channel: Po1
------------
Age of the Port-channel = 00d:14h:01m:55s
Logical slot/port = 2/1 Number of ports = 2
GC = 0x00000000 HotStandBy port = null
Port state = Port-channel
Protocol = PAGP
Port Security = Disabled
Ports in the Port-channel:
Index Load Port EC state No of bits
------+------+------+------------------+-----------
0 00 Gig0/2 On 0
0 00 Gig0/1 On 0
Time since last port bundled: 00d:06h:29m:45s Gig0/1
Switch#sh spanning-tree interface port-channel 1
no spanning tree info available for Port-channel1
01-23-2014 01:06 PM
Hello
Hum it seems you have created the port-channel first then confined the physical interfaces plus the interfaces looks like they are not are not active given the stp and ether-channel readouts
You say you need to aggregate physical port for server connection but at present the physical ports are trunked which indicates switch to switch connections -(would expect to see server porta in access mode)
Anyway please take a look at this post:
https://supportforums.cisco.com/message/4146391#4146391
Res
Paul
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