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Etherchannel Issue

Posted on 2010-08-23
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Last Modified: 2012-05-10
I have setup EtherChannel between 2 cisco 3750 switches and have and having a slight issue. Ports 45-48 are the ports configured for EtherChannel. Some how port 48 on switch 1 was unplugged and a room with about 7  systems could not reach the switch 2 configured with EtherChannel. the machines could onle access other systems that are physically plugged into the switch 1 but not the second switch configured with EtherChannel. All other machines plugged into switch 1 can get to switch 2 and out to the internet just not these 7 systems. When i plugged port 48 back in all the systems could reach switch 2 and get out to the internet. my question is, why would this happen? is my configuration worng?

Switch 1:

sh ver
Cisco IOS Software, C3750 Software (C3750-IPBASEK9-M), Version 12.2(50)SE2, RELEASE SOFTWARE (fc2)
Copyright (c) 1986-2009 by Cisco Systems, Inc.
Compiled Fri 15-May-09 21:29 by nachen
Image text-base: 0x00003000, data-base: 0x01900000

interface Port-channel1
 description Link to sw02
 switchport trunk encapsulation dot1q
 switchport mode trunk

interface GigabitEthernet1/0/45
 description Link to sw02
 switchport trunk encapsulation dot1q
 switchport mode trunk
 channel-group 1 mode on
!
interface GigabitEthernet1/0/46
 description Link to sw02
 switchport trunk encapsulation dot1q
 switchport mode trunk
 channel-group 1 mode on
!
interface GigabitEthernet1/0/47
 description Link to sw02
 switchport trunk encapsulation dot1q
 switchport mode trunk
 channel-group 1 mode on
!
interface GigabitEthernet1/0/48
 description Link to sw02
 switchport trunk encapsulation dot1q
 switchport mode trunk
 channel-group 1 mode on

Switch 2:

sh ver
Cisco IOS Software, C3560 Software (C3560-IPBASEK9-M), Version 12.2(50)SE1, RELEASE SOFTWARE (fc2)
Copyright (c) 1986-2009 by Cisco Systems, Inc.
Compiled Mon 06-Apr-09 08:00 by amvarma
Image text-base: 0x00003000, data-base: 0x01900000

interface Port-channel1
 description Link to sw01
 switchport trunk encapsulation dot1q
 switchport mode trunk

interface GigabitEthernet0/45
 description Link to sw01
 switchport trunk encapsulation dot1q
 switchport mode trunk
 channel-group 1 mode on
!
interface GigabitEthernet0/46
 description Link to sw01
 switchport trunk encapsulation dot1q
 switchport mode trunk
 channel-group 1 mode on
!
interface GigabitEthernet0/47
 description Link to sw01
 switchport trunk encapsulation dot1q
 switchport mode trunk
 channel-group 1 mode on
!
interface GigabitEthernet0/48
 description Link to sw01
 switchport trunk encapsulation dot1q
 switchport mode trunk
 channel-group 1 mode on
0
Comment
Question by:dufff
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7 Comments
 
LVL 24

Expert Comment

by:rfc1180
ID: 33505395
the configs look fine, the question is, what is the state of the port channels and ports now and what were they before?

Can you post:

show int status
show spanning int po1
show int trunk
show etherch sum


Billy
0
 

Author Comment

by:dufff
ID: 33506720
Port      Name               Status       Vlan       Duplex  Speed Type
Gi0/1     Link to rtr01 connected    trunk        full   1000 10/100/1000BaseTX
Gi0/2     Reserved for Backu connected    401        a-full a-1000 10/100/1000BaseTX
Gi0/3     Admin LAN          connected    401        a-full a-1000 10/100/1000BaseTX
Gi0/4     Admin LAN          notconnect   401          auto   auto 10/100/1000BaseTX
Gi0/5     Admin LAN          connected    401        a-full a-1000 10/100/1000BaseTX
Gi0/6     Admin LAN          connected    401        a-full  a-100 10/100/1000BaseTX
Gi0/7     Admin LAN          connected    401        a-full a-1000 10/100/1000BaseTX
Gi0/8     Admin LAN          notconnect   401          auto   auto 10/100/1000BaseTX
Gi0/9     Admin LAN          connected    401        a-full  a-100 10/100/1000BaseTX
Gi0/10    Admin LAN          notconnect   401          auto   auto 10/100/1000BaseTX
Gi0/11    Admin LAN          notconnect   401          auto   auto 10/100/1000BaseTX
Gi0/12    Admin LAN          notconnect   401          auto   auto 10/100/1000BaseTX
Gi0/13    Admin LAN          notconnect   401          auto   auto 10/100/1000BaseTX
Gi0/14    Admin LAN          notconnect   401          auto   auto 10/100/1000BaseTX
Gi0/15    Admin LAN          notconnect   401          auto   auto 10/100/1000BaseTX
Gi0/16    Admin LAN          notconnect   401          auto   auto 10/100/1000BaseTX
Gi0/17    Admin LAN          notconnect   401          auto   auto 10/100/1000BaseTX
Gi0/18    Admin LAN          notconnect   401          auto   auto 10/100/1000BaseTX
Gi0/19    Admin LAN          notconnect   401          auto   auto 10/100/1000BaseTX
Gi0/20    Admin LAN          notconnect   401          auto   auto 10/100/1000BaseTX
Gi0/21    Admin LAN          notconnect   401          auto   auto 10/100/1000BaseTX
Gi0/22    Admin LAN          notconnect   401          auto   auto 10/100/1000BaseTX
Gi0/23    Admin LAN          notconnect   401          auto   auto 10/100/1000BaseTX
Gi0/24    Admin LAN          notconnect   401          auto   auto 10/100/1000BaseTX
Gi0/25     VPN NETWORK connected    102        a-full a-1000 10/100/1000BaseTX
Gi0/26    DR SITE LAN        connected    403        a-full a-1000 10/100/1000BaseTX
Gi0/27    Production LAN     notconnect   402          auto   auto 10/100/1000BaseTX
Gi0/28    Production LAN     notconnect   402          auto   auto 10/100/1000BaseTX
Gi0/29    Production LAN     notconnect   402          auto   auto 10/100/1000BaseTX
Gi0/30    Production LAN     notconnect   402          auto   auto 10/100/1000BaseTX
Gi0/31    Production LAN     notconnect   402          auto   auto 10/100/1000BaseTX
Gi0/32    Production LAN     notconnect   402          auto   auto 10/100/1000BaseTX
Gi0/33    Production LAN     notconnect   402          auto   auto 10/100/1000BaseTX
Gi0/34    Production LAN     notconnect   402          auto   auto 10/100/1000BaseTX
Gi0/35    Production LAN     notconnect   402          auto   auto 10/100/1000BaseTX
Gi0/36    Production LAN     notconnect   402          auto   auto 10/100/1000BaseTX
Gi0/37    Production LAN     notconnect   402          auto   auto 10/100/1000BaseTX
Gi0/38    Production LAN     notconnect   402          auto   auto 10/100/1000BaseTX
Gi0/39    Production LAN     notconnect   402          auto   auto 10/100/1000BaseTX
Gi0/40    Production LAN     notconnect   402          auto   auto 10/100/1000BaseTX
Gi0/41    Production LAN     notconnect   402          auto   auto 10/100/1000BaseTX
Gi0/42    Production LAN     notconnect   402          auto   auto 10/100/1000BaseTX
Gi0/43    Production LAN     notconnect   402          auto   auto 10/100/1000BaseTX
Gi0/44    Production LAN     notconnect   405          auto   auto 10/100/1000BaseTX
Gi0/45    Link to sw02  connected    trunk      a-full a-1000 10/100/1000BaseTX
Gi0/46    Link to sw02  connected    trunk      a-full a-1000 10/100/1000BaseTX
Gi0/47    Link to sw02  connected    trunk      a-full a-1000 10/100/1000BaseTX
Gi0/48    Link to sw02  connected    trunk      a-full a-1000 10/100/1000BaseTX
Gi0/49                       notconnect   1            auto   auto Not Present
Gi0/50                       notconnect   1            auto   auto Not Present
Gi0/51                       notconnect   1            auto   auto Not Present
Gi0/52                       notconnect   1            auto   auto Not Present
Po1       Link to sw02  connected    trunk      a-full a-1000



sw01#sw01#show spanning int po1

Vlan                Role Sts Cost      Prio.Nbr Type
------------------- ---- --- --------- -------- --------------------------------
VLAN0001            Desg FWD 3         128.56   P2p
VLAN0100            Desg FWD 3         128.56   P2p
VLAN0102            Desg FWD 3         128.56   P2p
VLAN0401            Desg FWD 3         128.56   P2p
VLAN0402            Desg FWD 3         128.56   P2p
VLAN0403            Desg FWD 3         128.56   P2p
VLAN0405            Desg FWD 3         128.56   P2p
VLAN0901            Desg FWD 3         128.56   P2p
sw01#

sw01#show int trunk

Port        Mode             Encapsulation  Status        Native vlan
Gi0/1       on               802.1q         trunking      1
Po1         on               802.1q         trunking      1

Port        Vlans allowed on trunk
Gi0/1       1-4094
Po1         1-4094

Port        Vlans allowed and active in management domain
Gi0/1       1,100,102,401-403,405,901
Po1         1,100,102,401-403,405,901

Port        Vlans in spanning tree forwarding state and not pruned
Gi0/1       1,100,102,401-403,405,901
Po1         1,100,102,401-403,405,901

sw01#show int trunk

Port        Mode             Encapsulation  Status        Native vlan
Gi0/1       on               802.1q         trunking      1
Po1         on               802.1q         trunking      1

Port        Vlans allowed on trunk
Gi0/1       1-4094
Po1         1-4094

Port        Vlans allowed and active in management domain
Gi0/1       1,100,102,401-403,405,901
Po1         1,100,102,401-403,405,901

Port        Vlans in spanning tree forwarding state and not pruned
Gi0/1       1,100,102,401-403,405,901
Po1         1,100,102,401-403,405,901
hway-sw01#show etherch sum
Flags:  D - down        P - bundled 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

        M - not in use, minimum links not met
        u - unsuitable for bundling
        w - waiting to be aggregated
        d - default port


Number of channel-groups in use: 1
Number of aggregators:           1

Group  Port-channel  Protocol    Ports
------+-------------+-----------+-----------------------------------------------
1      Po1(SU)          -        Gi0/45(P)   Gi0/46(P)   Gi0/47(P)  
                                 Gi0/48(P)  
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LVL 24

Expert Comment

by:rfc1180
ID: 33506769
everything looks fine; the only thing that I can think of what happen is the the load balancing of the ports on the etherchannel; depending on the load balancing algorithm you are using, maybe those 7 servers were using port 1/48 (did you check other destinations besides the destination to switch2). It is hard to say what the issue was, are you able to replicate the issue, if, I would check from layer 3 to layer 4 while the issue is occurring. Technically, if you loose one link, traffic is suppose to continue on the other links after calculation. So you could be running into a bug on the IOS version you are using, but without other solid evidence, it is really hard to say.

Billy
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Author Comment

by:dufff
ID: 33506788
OK I can call Cisco on that. I just wanted to make sure my config is correct and make sure the load balancing is supposed to fail over. Do you know of any troubleshooting techniques i can try?
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LVL 50

Accepted Solution

by:
Don Johnston earned 500 total points
ID: 33510479
>When i plugged port 48 back in all the systems could reach switch 2 and get out to the internet. my question is, why would this happen?

On the 3750, etherchannel distributes traffic over the physical links based on the MAC or IP address(es). The default is the source MAC address. In the case of 4 links, the last two bits of the source MAC address is used (00, 01, 10, 11).

In the event one of the links fails, the traffic on that link is supposed to fail over to one of the other links. For some reason, this doesn't appear to be happening. It could be because you're using "on" mode. I would suggest using "desirable" mode since this creates (and manages) the channel only if it can be negoiated with the other switch.

So try changing the config on all the interfaces in the channel group (on both switches) to:

channel-group 1 mode desirable


0
 

Author Comment

by:dufff
ID: 33512900
OK, thanks I will try that and let you kow how it goes
0
 

Author Closing Comment

by:dufff
ID: 33629939
Thanks so much, that resolved the issue.
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