Etherchannel Load-Balance

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Nov 12th, 2009
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Hi experts,


We have got two Cisco 2950 SW LACP configured with on fe. The LACP channel is up working fine we can view the BW aggregation 100+100 = 200M, but what we found among two ports only one is receiving and forwarding the packets. Is there any idea why ?


Thank you

Uttam

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Jon Marshall Thu, 11/12/2009 - 07:34
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Uttam


The 2950 support src and dst mac load-balancing only. So if for example you have src mac load-balancing then the same src host will always use the same link. Have a read of this doc which explains it all in more detail -


http://www.cisco.com/en/US/tech/tk389/tk213/technologies_tech_note09186a0080094714.shtml#cat2950_3550


Jon

adamclarkuk_2 Thu, 11/12/2009 - 07:38
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Hi Uttam


If both interfaces are up and in use (check the output of show etherchannel summary) then depends on the flows going through the port channel and which load balancing method you are using.


Here is a link on etherchannel Load balancing and has a section on the 2950:-

http://www.cisco.com/en/US/tech/tk389/tk213/technologies_tech_note09186a0080094714.shtml

urs.shrestharana Thu, 11/12/2009 - 09:14
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Hi,


We are using source MAC address load balancing. The sh etherchannel summary shows:

Group Port-channel Protocol Ports

------+-------------+-----------+-----------------------------------------------

1 Po1(SU) LACP Fa0/23(P) Fa0/24(Pd)


The traffic on port 0/23 is full, but no traffic running on port fa0/24.


Thank you

Ramesh

iyde Thu, 11/12/2009 - 12:44
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Hi.


Could you share the config of interface Fa0/23 and F0/24?

I see that the code for Fa0/24 is (Pd) while the code for Fa0/23 is (P) in your show etherchannel summary. I wonder if that has anything to do with the problem. I've never seen that on my switches, as far as I remember.


HTH, Ingolf

urs.shrestharana Fri, 11/13/2009 - 09:20
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Hi Ingolf,


Here is the configuration of port fa0/23 and fa0/24



interface FastEthernet0/23

description " EtherChannel Source Port "

switchport trunk allowed vlan 2-500

switchport mode trunk

switchport nonegotiate

speed 100

duplex full

no cdp enable

channel-group 1 mode active

channel-protocol lacp

end


interface FastEthernet0/24

description " EtherChannel Source Port "

switchport trunk allowed vlan 2-500

switchport mode trunk

switchport nonegotiate

speed 100

duplex full

no cdp enable

channel-group 1 mode active

channel-protocol lacp

end


We have applied same configuration on Cisco 2970 and it is working quietly.


Thank you,


Uttam



Giuseppe Larosa Fri, 11/13/2009 - 09:34
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Hello Ramesh,

I've faced the same issue some days ago on a C2950 LRE.


the 'd' is the default port.


It has come out that on C2950 LRE ports and some other platforms like C2924 bundles are formed but only one link is used and the other one is just kept as an hot standby.


This was unclear in documentation we opened a service request and we got this feedback.


So what is on the other side of your port-channel?


It may be the device on the other side that leads to this as it happened in our case.



Hope to help

Giuseppe


urs.shrestharana Fri, 11/13/2009 - 10:40
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Hi Giuseppe,


on the other side :


# sh etherchannel summary



Number of channel-groups in use: 1

Number of aggregators: 1


Group Port-channel Protocol Ports

------+-------------+-----------+-----------------------------------------------

1 Po1(SU) LACP Fa0/21(Pd) Fa0/22(P)



ports are connected :

21 == 23

22 == 24


among them only the port 21 connected to 23 is in use, the port 22 connected with 24 its completely idle/hot-standby.


thank you,

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