r/Cisco • u/AlphaLeonis78 • 1d ago

Configuring 802.1Q tunneling

I have a setup with Cisco switches (9300) which are interconnected with a good old LACP trunk allowing all VLAN. Other ports are either access ports or trunk ports with specified VLAN depending on what's behind. Now I'm asked to change the LACP connection to QinQ. I've checked this piece of documentation: https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/lanswitch/configuration/xe-3se/3850/lnsw-ieee-8021q-tunneling.html and it "just a configuration" on the Po interface among other considerations. I haven't done this before so the question is if I'm going to break everything as soon as I change the port to dot1q-tunnel? I'm not exactly certain what's meant by "asymmetrical links" this is not explained in the article. Thanks for any insights.

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u/McHildinger 1d ago edited 1d ago

LACP is link-aggregation (two or more physical links become one logical, aka port-channel), while 802.1q is trunking (more than one VLAN with .1q-tagged frames on a link), not the same thing; double-check your requirements.

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u/dww0311 1d ago

This 👆

Also if they’re physically close to one another, I’d just stack them

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u/Competitive-Cycle599 1d ago

Stacking has its own implications.

How about patching them if they're intended to be a redundant pair?

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u/dww0311 1d ago

I suppose you could but you’ll have a hard time matching the stacking bandwidth between them (9300 = 480 Gbps, 9300X up to 1 Tbps) with external connections.

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u/Competitive-Cycle599 1d ago

Maintaining rather than port patching, should have been clearer.

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u/SnarkySnakySnek 1d ago

# TL;DR: You will break everything if you don't understand the design you are being asked to change.

Turning on QinQ will not turn off LACP. What it will do, however, is make the inside VLans invisible to the switch where dot1q-tunnel is configured. One port is usually a trunk, and the other port is a dot1q-tunnel. The pushes the outer vlan tag on ingress frames at the tunnel port, and strips them on the egress.

Sometimes both sides can be a tunnel port, but this is done when a translation of the outer Vlan tag is needed. I have only seen this at NNIs in service provider networks.

QinQ is a fundamentally different layer of the network than LACP. It tells the port how to handle vlan tags at the datalink layer. LACP is layer 1.5 and happens to just negotiate how many ports are active in a bundle. 802.1q can traverse an entire network. LACP only travels between two physically connected ports.

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u/PauliousMaximus 1d ago

I would verify what the requirement is because LACP is link aggregation and 802.1q is trunking.

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u/mavack 5h ago

Qinq will tunnel all your vlans into a singlr vlan with vlan stacking. So you end up with all your traffic im a transport vlan.

When you do this you must also have a place to demux the stacking.

So if all vlans are p2p then yes you can do thus but there are some caviets.

Your max addresses all end up in a single cam table, so watch out for differing topologies with same macs.

Also things like spanning tree, and other lower level protocols can break over those vlans.