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STP and LACP issues

geronimo1000
Occasional Visitor

STP and LACP issues

I'd like to eliminate STP from our network and just use LACP, but I've run into some issues.

One of our switches has RSTP enabled and passive LACP enabled (I believe passive LACP is the default setting). If I disable STP on the switch, I lose connectivity. Why would this occur? I can understand enabling STP causing a temporary blocking state, but it is my assumption that disabling STP should not cause any blocking. Is the loss of connectivity somehow caused by LACP?

Also, in some instances, LACP will correctly configure itself on a pair of HP switches when two cables are attached. In some cases it will not. Does anyone know why LACP might automatically configure itself only some of the time?

What I'd like to do is disable STP and LACP on all ports, then go back and manually configure active LACP on the ports that require it.

Sometimes, after configuring active LACP on one port, I lose connectivity to the switch. Has anyone else experienced this?
4 REPLIES
geronimo1000
Occasional Visitor

Re: STP and LACP issues

I forgot to mention that the switches involved are a 5308xl and HP2848's
Mohieddin Kharnoub
Honored Contributor

Re: STP and LACP issues

Hi

Usually, LACP requires full-duplex (FDx) links of the same media type (10/100/1000Base-T).

For RSTP, its recomended to configure all ports not connected to another switches to be Edge Port : "spanning-tree [port list] edge-port".

Now for what you asked "Does anyone know why LACP might automatically configure itself only some of the time?"
Do you have any Trunk configured between the switches ? do you use Dynamic LACP ?

Good Luck !!!
Science for Everyone
geronimo1000
Occasional Visitor

Re: STP and LACP issues

The person who configured the switch enabled RSTP without making configuration changes on individual ports. LACP is set to passive on every port. If I disable RSTP then I lose connectivity, but I'm not sure why. Re-enabling RSTP restores connectivity.

On some switches, connecting two identical links to an identical switch causes the LACP trunk to form automatically. Other times it does not. Also, in some instances, after enabling active LACP on one port, I lose connectivity.

I'm going to disable STP completely as it isn't useful with our current topology. I also plan to disable passive LACP on every port and actively enable it on the necessary ports.

I was hoping someone might have an explanation for why connectivity is lost when STP is disabled, and also why connectivity is lost when one LACP link is manually activated.
Mohieddin Kharnoub
Honored Contributor

Re: STP and LACP issues

Hi

Attach the config of your switches, that will be helpful to understand your scenario, and whats going on.
Enable Syslog on 5300, and dump its messages to a Syslog server, then try to do some debug so it may be clear to you what going on from the messages you see.

Good Luck !!!
Science for Everyone