Loss of conectivity between 2 CISCO 4500

[Jose Francisco Prieto Lopez]

Hi all,

we have two cisco 4500 running with a port-channel:

Config on both cisco:

int giga 1/1

sw tr all vlan 1-10

sw mo tr

int giga 2/1

sw tr all vlan 1-10

sw mo tr

int port-channel 1

sw tr all vlan 1-10

sw mo tr

Now we added a new vlan (11) and we tried to add it to both CAT

CAT_2

int giga 1/1

sw tr all vlan 1-11

int giga 2/1

sw tr all vlan 1-11

At this moment we lost the connectivity between two nodes.

then we added the same config to CAT1

int giga 1/1

sw tr all vlan 1-11

int giga 2/1

sw tr all vlan 1-11

int port-channel 1

sw tr all vlan 1-11

But no ping to CAT_2, so we had to go to CAT_2 and via console add the "int port-channel" config.

Is common that lost of conectivity between two nodes?

thanks for your replies

Jose

[Jon Marshall]

Jose

You should not add the configuration to the individual interfaces and that is probably why you lost connectivity.

You should have added the configuration to the port channels and then it should have worked.

Jon

[Jose Francisco Prieto Lopez]

Thanks Jon for your reply.

Maybe i should have configured only the port-channel interface...

As far as i know, i allways have configured trunks vlan in interfaces and in port-channel.

What i do not understand is if vlans defined in the interface port-channel are the mandatory vlans, if i define new vlans in interface physical why it shutdowns the whole conenctivy between catalyst. I can understand a missmatch in vlan definitions but not loss of connectivity between both devices.

sorry for my english and thx for your  quick help

Jose

[Jon Marshall · Accepted solution]

Jose

It is a bit of a lottery to be honest when you change the physical ports.

As soon as you configured one of the ports with the new vlan then you have an inconsistency between the physical ports in the etherchannel.

So the port will drop out of the etherhchannel.

This can then cause STP issues because you now have two connections between the switches but they are not in an etherchannel.

So always apply the change to port channel interface because then that is applied to all the ports and they remain in the etherchannel.

Jon

[Madhukrishnan Gopinathan Nair]

I think what Jon said is 100 % correct here. One more thing you can do is , it is better to use the keyword add , rather than overwritting the whole vlan.

switchport trunk allowed vlan add <vlan to be added>

Thanks,

M

[Jose Francisco Prieto Lopez]

Thanks for your reply.

Was a nice commet "It is a bit of a lottery to be honest when you change the physical ports"    =)

Have a nice day and weekend.

Thanks a lot

Best regards,

Jose

[Madhukrishnan Gopinathan Nair]

Dear Jose,

If the posts helped, please feel free to mark it answered.

Thanks,

M

[Madhukrishnan Gopinathan Nair]

Dear Jose,

Can you please share the logs if you have at that time?

Thanks,

M

[Jose Francisco Prieto Lopez]

I am so sorry, but we do not have those logs.

thanks for your help and time

Jose