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Ethernet Switches & Routers

Posts: 44
Registered: ‎07-08-2011

Convert single trunk to 2 port trunk

We have a fiber connection between 2 switches. Actually 1 switch is connected via a fiber port on a 48 port switch to a fiber network among other links. also connected to that fiber switch is another 48 port switch with 1 of it's 4 gbic module ports connected to that fiber switch. they share a L2 vlan that no one else is in.

basically we've added a 2nd gbic module to each of the 48 port switches so we can make the connection between them 2 gbps.

the problem is they are very far apart and I'm trying to reduce downtime as much as possible and have no one who can be at the other switch while I'm at the other one. so here's my thoughts:

First: connect fiber cable between switch A port 2 to fiber switch and between switch B and fiber switch


drop trunk connection on switch A.

recreate trunk on switch A using both ports. this will still only run at most at 1 gbps because switch B only has a single connection. but link is up

go to switch B and drop trunk and recreate trunk like above.

Option 2:

remote to switch B from switch A. drop trunk

drop trunk on switch A

recreate 2 port trunk on switch A

go to switch B and recreate 2 port trunk on it.

I'm hoping Option 1 is the right path as it allows the least down time.

can someone show me the commands to do this? I'm inheriting these switches and have very little experience with them except the GUI.

Super Contributor
Posts: 1,087
Registered: ‎12-13-2009

Re: Convert single trunk to 2 port trunk

Hi JackOfTrades,

     Yes you can go ahead with option 1. Note you could also disable the port on Switch B, then plug in the new link and the config needed for LACP, then go back to switch A configure LACP then SSH over to switch B and enbale the port.

FGS648 Switch(config)#interface ethernet 1/1/47 to 1/1/48

FGS648 Switch(config-mif-1/1/47-1/1/48)#link-aggregate off

FGS648 Switch(config-mif-1/1/47-1/1/48)#link-aggregate active



Posts: 44
Registered: ‎07-08-2011

Re: Convert single trunk to 2 port trunk

According to my switch, there's no way to disable an individual port inside a trunk. According to this link there's a way to do this, but my switch does not support it.


In any case, turns out the hardware our provider has in between the two sites is not capable of handling a true trunk, so we need to work with them on this first hand. I did option 1 and it caused a loop. Not good.

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