LACP

[saleh.kouhsangin]

Hello guys

I have a question about lacp hot-standby interfaces,according to the cisco documents "When enabled, LACP tries to configure the maximum number of LACP-compatible ports in a channel,up to a maximum of 16 ports. Only eight LACP links can be active at one time. The software places any
additional links in a hot-standby mode. If one of the active links becomes inactive, a link that is in the hot-standby mode becomes active in its place."

Now my question is if i want to configure just 4 interfaces as active and 4 interfaces as hot-standby,what i can do?

is there any configuration for it?

sw1(3750)

sw2(3750)

Regards

[niko]

Hi,

Try setting #lacp max-bundle X in interface configuration mode, where X is desired number of ports to be active in EtherChannel.

[saleh.kouhsangin]

based on cisco docs

 http://www.cisco.com/c/en/us/td/docs/switches/lan/catalyst3750x_3560x/software/release/12-2_53_se/configuration/guide/3750xscg/swethchl.html

cannot use this command

[niko]

Yes, max-bundle is not supported for 3750, that is correct.

[Jon Marshall]

Just out of interest why would you want to do this ?

I can't see the point because the links in standby cannot be used for anything else so you may as well use them all in your etherchannel.

Is it because you are trying to limit the actual amount of bandwidth between a pair of switches.

Jon

[saleh.kouhsangin]

Thanks Jon,just i'was reviewing cisco documents and found that then i asked myself how can i do it?

You said "hot-standby interfaces cannot be used for anything else" thanks i didnt know this,but how can we make it?

how to configure 4 interfaces as hot-standby?when i configured lacp on my selected interfaces then is it necessary to define hot-standby interfaces?I have enabled lacp on 4 interfaces so hot-standby interfaces how can be selected?

[niko]

LACP port priority can be changed in order to choose the ports for the Etherchannel (EC). Under interface configuration mode: #lacp port-priority <number>.

Given the specifics for the hash calculation algorithm, 2, 4 or 8 ports are optimal choice for port count in EC, so maybe setting maximum links to 4 and leaving 1 as standby can make sense. Or technical limitation of paired device. Who knows, it will never hurt to know the possibility at least.

[Jon Marshall]

You don't have to configure standby interfaces, it is just an option you can use.

And as far as I can see you would only use it if you wanted extra redundancy.

So no, it's not necessary when you configure an etherchannel.

Jon