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etherchannel with stacked switches on 3750

Hi,

i have got cisco 3750 3 Nos. stacked together, below are the config. for etherchannel & the err. msg. i get.

interface gigabit 1/0/25

switchport mode access

channel-group 1 mode desirable

once if i do that, i get "creating a port-channel interface Port-channel 1

interface gigiabit 2/0/25

switchport mode acess

channel-group 1 mode desirable

i get error msg. "%With PAgP enabled, all ports in the Channel should belong to the same switch Command rejected (Port-channel1, Gi2/0/25): Invalid etherchnl mode"

actually if i do that in the same switch i mean 1/0/26,command is accepting. so how to proceed, bcoz i thought i will share the load across 3 switches for etherchanneling.

6 REPLIES
Silver

Re: etherchannel with stacked switches on 3750

If I understand you correctly you would like to create an etherchannel within the same switch stack, right?

If the swithc is stacaked using stackwise and has one active switch engine this is not going to work because all switching is done by the master switch, designated as switch "1". Hence 1//.

The load is carried through the shared backplane of the switch fabric, etherchannel will do you good when you break the stack and cable the switches idependently.

HTH

Leon

* Please rate posts if you find them helpful.

Re: etherchannel with stacked switches on 3750

actually, i wanted to create etherchannel between cisco 6509 & 3750, so i thought i will connect 3 cables in 3750 across 3 switches for etherchanneling, eg. 1 cable in switch-1, 1 cable in switch-2 & other cable in switch-3, so that even if 1 switch fails, thru the other cables connected on remaining 2 3750's there will be connectivity for 6509. so this is my requirement. i hope you have understood my question.

Re: etherchannel with stacked switches on 3750

Hi Anand,

Is it a crossed stacked?

EtherChannel groups running PAgP can coexist on the same switch or on different switches in the stack (but not in a cross-stack configuration).

For cross-stack EtherChannel configurations, disable PAgP and LACP on all ports targeted for the EtherChannel by using the channel-group channel-group-number mode on interface configuration command. Before adding a stack member port to an existing EtherChannel, manually disable PAgP and LACP on all the ports that are members of the channel group, and then manually configure the cross-stack EtherChannel. PAgP and LACP are not supported on cross-stack EtherChannels.

Have a look at this link for etherchannel guidelines when stacking in configured

http://www.cisco.com/univercd/cc/td/doc/product/lan/cat3750/12220se/3750scg/swethchl.htm#wp1021856

HTH, if yes please rate the post.

Ankur

Re: etherchannel with stacked switches on 3750

Hi Ankur,

thanks for the response,since the etherchannel requires "switchport mode trunk encapsulation dot1q & switchport mode trunk" for VLAN, i thought i will put that command in the "interface port-channel1" but it is not accepting.how do i proceeed, currently trunking is happening in one of the physical port, since etherchanneling is configured, we need to put those commands in "interface port-channel1" isn't? so how i do that? thanks in advance

New Member

Re: etherchannel with stacked switches on 3750

You cannot use PAgP for etherchannel across seperate 3750's in a stack.

You can set the channel mode to 'on' and it will work or they must come from the same swtich in the stack.

The following is taken from the cat 3750 config guide

http://www.cisco.com/en/US/products/hw/switches/ps5023/products_configuration_guide_chapter09186a00801cdea1.html#1154336

For cross-stack EtherChannel configurations, disable PAgP and LACP on all ports targeted for the EtherChannel by using the channel-group channel-group-number mode on interface configuration command. Before adding a stack member port to an existing EtherChannel, manually disable PAgP and LACP on all the ports that are members of the channel group, and then manually configure the cross-stack EtherChannel. PAgP and LACP are not supported on cross-stack EtherChannels.

If cross-stack EtherChannel is configured and the switch stack partitions, loops and forwarding misbehaviors can occur.

HTH

N

New Member

Re: etherchannel with stacked switches on 3750

The PAgP protocol is not supported on cross- stack EtherChannels.

Do not get scared, You can create an EtherChannel on a standalone switch, on a single switch in the stack, or on multiple switches in the stack (known as cross-stack EtherChannel)!

How?

For cross-stack EtherChannel configurations, ensure that all ports targeted for the EtherChannel are either configured for LACP or are manually configured to be in the channel group using the

"channel-group channel-group-number mode on" interface configuration command. The PAgP protocol is not supported on cross- stack EtherChannels.

If cross-stack EtherChannel is configured and the switch stack partitions, loops and forwarding

misbehaviors can occur.

Do not forget to rate this! Have fun!

Mohamed BEN HASSINE

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