Equipment Support > Hardware By Brand > Cisco > [HELP] Etherchannel Configuration - A bit Confused

[HELP] Etherchannel Configuration - A bit Confused

1

spanning tree.
spanning tree.
spanning tree.

First change your port-channel mode to active on the member links. Also do a show etherchan sum and make sure the port chan is all up and happy. Double check the show cdp neighbor ports are also configured for mode active.

Then locate the spanning tree root bridge for all vlans, make sure its on the desired switch (primary HSRP gateway).

Do a show span and see what kind of spanning tree is running. Per-vlan rapid spanning tree or multiple spanning tree will be your best bet. Single instance rapid spanning tree will also work for a lab, but is somewhat less desirable in TRW.

reply to RFP
Tagging along with NOSX on this one:

Question #1: , Keep in mind "all ports" of your etherchannel "must" have identical settings (i.e., speed, etherchannel group assignment, etc...).

Question #2: Do a "sh int Po1 trunk" (if Po1 is te number designator) to see if the vlan your users are having issues with is allowed through the trunk.

Question #3:As stated by NOSX, check spanning-tree. It sounds like one of your ports is in "blocking" mode, then going to "forwarding" mode. As mentioned in "question #2," make sure the settings for your ports are identical (i.e, speed, duplex, etc...).

Here's a couple of resources that might help:

1) Keith Barker, CCIE #6783 - Spanning Tree

reply to nosx

CORE_A#show etherchannel summary 
Flags:  D - down        P - in port-channel
        I - stand-alone s - suspended
        H - Hot-standby (LACP only)
        R - Layer3      S - Layer2
        U - in use      f - failed to allocate aggregator
        u - unsuitable for bundling
        w - waiting to be aggregated
        d - default port
 
Number of channel-groups in use: 2
Number of aggregators:           2
 
Group  Port-channel  Protocol    Ports
------+-------------+-----------+----------------------------------------------
 
1      Po1(SU)           -      Gig0/1(P) Gig0/2(P) 
2      Po2(SU)           -      Fa0/23(P) Fa0/24(P) 
 

CORE_A#show cdp neighbors (only from CORE_A#)
Capability Codes: R - Router, T - Trans Bridge, B - Source Route Bridge
                  S - Switch, H - Host, I - IGMP, r - Repeater, P - Phone
Device ID    Local Intrfce   Holdtme    Capability   Platform    Port ID
CORE_B       Por 2            152                    3560        Fas 0/23
CORE_B       Por 2            152                    3560        Fas 0/24
CORE_B       Por 2            152                    3560        Por 2
6idf1        Por 1            147                    3560        Gig 0/1
6idf1        Por 1            147                    3560        Gig 0/2
6idf1        Por 1            147                    3560        Por 1
CORE_A#
 

core a
 
VLAN0001
  Spanning tree enabled protocol ieee
  Root ID    Priority    32769
             Address     000A.F379.69C9
             Cost        9
             Port        27(Port-channel 2)
             Hello Time  2 sec  Max Age 20 sec  Forward Delay 15 sec
 
  Bridge ID  Priority    32769  (priority 32768 sys-id-ext 1)
             Address     0090.21A0.5A08
             Hello Time  2 sec  Max Age 20 sec  Forward Delay 15 sec
             Aging Time  20
 
Interface        Role Sts Cost      Prio.Nbr Type
---------------- ---- --- --------- -------- --------------------------------
Fa0/2            Desg FWD 19        128.2    P2p
Po2              Root FWD 9         128.27   Shr
Gi0/1            Desg FWD 4         128.25   P2p
Gi0/2            Desg FWD 4         128.26   P2p
 
core b
 
VLAN0001
  Spanning tree enabled protocol ieee
  Root ID    Priority    32769
             Address     000D.BD58.18B3
             This bridge is the root
             Hello Time  2 sec  Max Age 20 sec  Forward Delay 15 sec
 
  Bridge ID  Priority    32769  (priority 32768 sys-id-ext 1)
             Address     000D.BD58.18B3
             Hello Time  2 sec  Max Age 20 sec  Forward Delay 15 sec
             Aging Time  20
 
Interface        Role Sts Cost      Prio.Nbr Type
---------------- ---- --- --------- -------- --------------------------------
Po2              Desg FWD 9         128.27   Shr
Fa0/1            Desg FWD 19        128.1    P2p
Gi0/1            Desg FWD 4         128.25   P2p
Gi0/2            Desg FWD 4         128.26   P2p
 
SW1
 
VLAN0001
  Spanning tree enabled protocol ieee
  Root ID    Priority    32769
             Address     000A.F379.69C9
             Cost        9
             Port        27(Port-channel 2)
             Hello Time  2 sec  Max Age 20 sec  Forward Delay 15 sec
 
  Bridge ID  Priority    32769  (priority 32768 sys-id-ext 1)
             Address     0010.112E.1DBA
             Hello Time  2 sec  Max Age 20 sec  Forward Delay 15 sec
             Aging Time  20
 
Interface        Role Sts Cost      Prio.Nbr Type
---------------- ---- --- --------- -------- --------------------------------
Fa0/1            Desg FWD 19        128.1    P2p
Po2              Root FWD 9         128.27   Shr
Po1              Desg FWD 0         128.28   Shr
 
SW2
 
VLAN0001
  Spanning tree enabled protocol ieee
  Root ID    Priority    32769
             Address     000A.F379.69C9
             This bridge is the root
             Hello Time  2 sec  Max Age 20 sec  Forward Delay 15 sec
 
  Bridge ID  Priority    32769  (priority 32768 sys-id-ext 1)
             Address     000A.F379.69C9
             Hello Time  2 sec  Max Age 20 sec  Forward Delay 15 sec
             Aging Time  20
 
Interface        Role Sts Cost      Prio.Nbr Type
---------------- ---- --- --------- -------- --------------------------------
Fa0/1            Desg FWD 19        128.1    P2p
Po2              Desg FWD 9         128.27   Shr
Po1              Desg FWD 0         128.28   Shr
 

reply to DocLarge

CORE_A#show interfaces trunk 
Port        Mode         Encapsulation  Status        Native vlan
Fa0/23      on           802.1q         trunking      1
Fa0/24      on           802.1q         trunking      1
Gig0/1      on           802.1q         trunking      1
Gig0/2      on           802.1q         trunking      1
Po1         on           802.1q         trunking      1
Po2         on           802.1q         trunking      1
 
Port        Vlans allowed on trunk
Fa0/23      1-1005
Fa0/24      1-1005
Gig0/1      1-1005
Gig0/2      1-1005
Po1         1-1005
Po2         1-1005
 
Port        Vlans allowed and active in management domain
Fa0/23      1
Fa0/24      1
Gig0/1      1
Gig0/2      1
Po1         1
Po2         1
 
Port        Vlans in spanning tree forwarding state and not pruned
Fa0/23      1
Fa0/24      1
Gig0/1      none
Gig0/2      none
Po1         none
Po2         1
 

The reason your switches are performing so poorly at failover and recovery is this:

VLAN0001
   Spanning tree enabled protocol ieee
 

VLAN0001
  Spanning tree enabled protocol rstp
 

conf t
  spanning-tree mode rapid-pvst
 end
wr
 

conf t
  spanning-tree vlan 1-4094 root primary
 exit
wr
 

conf t
  spanning-tree vlan 1-4094 root secondary
 exit
wr
 

reply to RFP
Hi, I'm new at configuring Etherchannel, I'm a bit puzzled at a few things and have a few questions:

1. After applying the commands below within the lab, the gigabit interfaces on switch (CORE A) remain amber color and not green, I don't know what this means, doing a "show interface g0/1 & 2" shows the g0/1 & 2 interfaces in the up/up state and everything seems ok. Does anyone know why the g0/1&2 interfaces remain amber?

Answer -- They remain amber because spanning tree is blocking that link . Your design has a built in loop and spanning tree has to block somewhere and that is the link it has chosen .

2. Second is, for some strange reason, everyone on the 6th floor is reachable from the 7th floor only via the Etherchannel from CORE B Gi0/1 & 2 to IDF SW 2. I think this has something to do with the amber color state of the CORE A gigabit interfaces.

Answer. Because the gig link is blocked it has to go all the way around the horn so to speak , its the only way to the gateway .

3. If one link from the Etherchannel going from SW 2 to CORE B goes down, the entire 6th Floor is unreachable for around 40 seconds. I don't know why this happens, but the amber links from CORE A to SW1 then turn green, allowing everyone from the 6th floor to be rechable only via CORE A to SW1. Why does this happen, and why does it take 40 seconds for the two floors to become reachable again? If there are two links in the Etherchannel isn't this supposed to help in the redundancy?

Answer -- Your etherchannel is not working , what you have is 2 individual trunk ports so one side is blocked . When one link goes down spanning tree runs (about 40 seconds) before the other link goes active. If the etherchannel was working properly it would not have this issue because spanning tree sees that as a single logical link so losing a single link would not cause spanning tree to run .

reply to RFP
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