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LAG Questions


Userlevel 1
Hi!

I want create a LAG configuration, but i have some questions.

1. can i configure it using ports to diferent slots?
2. once configured if the master port pass to down state , everything LAG link is down?

Regards

14 replies

Userlevel 6
Hello Daniel,

You can use any of the ports in a stack or a chassis to create a lag. If the master port goes down a new master port will take over.
Userlevel 4
1) within one stack - yes
2) no, you create virtual port - LAG - and it is "link up" while one of the ports, that belong to LAG, is linked
Userlevel 1
Hi Daniel,
Yes, you can have ports from different slots as long as the ports are off the same speed ... you cannot mix 1G with 10G.
If the master port goes down, one of the member ports takes over the LAG mastership. So having one port go down in a LAG does not break the entire LAG.

Hope this helps .
Userlevel 3
Hi Daniel,

I assume this is about EXOS firmware (Summit switches or BD chassis). Yes, of course you can build a lag with ports on different blades / stack members. They have to be the same speed though, e.g. 2 x SFP 1 Gig. And when the Master goes down, the LAG remains active!

For the record, with EOS you might want to enable singleportlag, to ensure that a 2-port LAG still remains active when 1 link fails / gets removed.
Userlevel 7
cbuchenau wrote:

Hi Daniel,

I assume this is about EXOS firmware (Summit switches or BD chassis). Yes, of course you can build a lag with ports on different blades / stack members. They have to be the same speed though, e.g. 2 x SFP 1 Gig. And when the Master goes down, the LAG remains active!

For the record, with EOS you might want to enable singleportlag, to ensure that a 2-port LAG still remains active when 1 link fails / gets removed.

EOS should be configured to disable LACP on all ports that are not intended to be used as part of a LAG. This is the default on the current hardware.

The "singleportlag" feature is needed after a LAG goes down completely (e.g. switch reboot) and then only one link comes up. Without "singleportlag" enabled, the link will not form a LAG, with "singleportlag" enabled it will.

With the older default of LACP active on all ports, single links connecting switches would form a LAG, until the number of supported LAGs on the switch was exhausted. The LAG number (lag.0.X) would be random, the configuration would often not be correct. Therefore EOS requires two links to form a LAG by default. It will still keep an established LAG as long as at least one participating port is active.
Userlevel 1
thanks guys!

so i can with a simple configuration? for example

SW1: enable sharing 5:1 grouping 5:2 6:1-2 algorithm address-based lacp

SW2:enable sharing 5:1 grouping 5:2 6:1-2 algorithm address-based lacp
Userlevel 6
The grouping needs to include the master port:

enable sharing 5:1 grouping 5:1-2,6:1-2 lacp

Unless you want to specify a different algorithm it will default to L2
Userlevel 1
Patrick Voss wrote:

The grouping needs to include the master port:

enable sharing 5:1 grouping 5:1-2,6:1-2 lacp

Unless you want to specify a different algorithm it will default to L2

thanks for the info Patrick
Userlevel 3
And in most cases you want to set the algorithm to L3_L4
Userlevel 3
MLAG even more flexibility
Userlevel 1
Last question: I need to restart computers to take the LAG configuration?
Userlevel 6
Hello Daniel,

I just need some clarification. By computers are you referring to the switch? or are you referring to a server on the other side. You should not need to reboot either for the LAG to take effect. LACP does need to be configured on both sides before the ports become part of the LAG.
Userlevel 1
Patrick Voss wrote:

Hello Daniel,

I just need some clarification. By computers are you referring to the switch? or are you referring to a server on the other side. You should not need to reboot either for the LAG to take effect. LACP does need to be configured on both sides before the ports become part of the LAG.

Yes Patrick i´m referring about Switch... tanks a lot.

regards
Userlevel 6
Daniel,

Starting with EXOS v15.7 you have the possibility of configuring the minimum number of links that must be active in a LAG before it is considered as "down".

Suppose you have two LAGs, each with 4 links, and that you configure one of them to be a backup of the other with the
configure ports primaryPort redundant secondaryPort {link [on | off]}[/code]command.

The secondary port (LAG) will not be activated until the first port (LAG) goes down. In a normal LAG that would happen only when ALL the links in the primary LAG go down. But if you have, say, 4 links in each LAG, you may want to switch to the secondary port (LAG) when two links in the primary LAG fail, so you don't lose performance.

You would do that with the
configure sharing port minimum-active min_links_active[/code]command.

Also, in EXOS v21.1 (and soon in EXOS v16.2) there's a new feature specifically for when you have ports on different modules in a modular switch, or different switches in a stack, that lets you modify how EXOS distributes traffic among the members of a LAG.

in the past, EXOS would always distribute traffic to all active members of a LAG. Now, you can specify a subset of the active member ports as elegible on a per slot basis. using the
configure sharing distribution-mode[/code]command.

You can specify the "local-slot" keyword to restrict distibution of traffic only to ports that are in the same slot (switch) where the traffic has been received. This prevents forcing traffic to traversethe backplane (or stack port)s to be transmitted through a LAG port in another slot (switch) in the chassis (stack), reducing latency.

You can also create "port lists" to indicate a subset of ports through which the traffic would be transmitted.

This only applies to unicast traffic.

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