Will QoS help me when L2 Loop in my switches?

[ty.chan007]

Last time, i had a very bad experience with L2 loop. All my switches were connected together as ring topology. We use REP to block redundancy link.

One of my colleagure was setting up a new link(VLAN) for one customer which was then cause a L2 loop. The CPU was hitting 100% and REP started to lost neighbors then we had a big outage.

I am thinking to deploy QoS on all REP switch (on trunk links from switch to switch) to give priority to control traffic like REP and some importance data VLAN. Can QoS help me to prevent this problem again ? of course, storm-control already implemented on all access-port.

Thanks,

[Abzal]

Hi,

It won't help, because when L2 loops occurs all frames (important VLAN traffic included) will be circulating on that segment. Only solution is Spanning-tree protocol that designed to prevent such thing. It builds loop-free tree by blocking redundant links.

Abzal

[ty.chan007]

although loop traffic is generated from certain VLAN only not all ?

[Abzal]

Actually it doesn't matter so much.

Only active VLANs (that you're created). Packets from VLANs that are sent during loop will be looped as well.

Network will be congested and switches will be highly loaded. And packets won't reach their destinations. Because they will be circulating on the network until you stop a loop.

Hope it will help.

[ty.chan007]

Thanks for clarification.

Let say I change from native L2 switch to MPLS L2 VPN.

Can L2 Loop impact the PE or P device ?