What does "l2protocol peer x" exactly do?

Question

i'm struggeling with some Layer2 Service within one of my customer's MPLS networks. My aim is to provide a L2VPN Service between two ISR4000 Boxes that act as CPE in my MPLS platform. This L2 Service should act as a failover for a primary Radio link. Transport in this Layer2 Service is working fine, but it is not transporting any STP BPDUs.

As the ISR4000 are only Bridging Frames between two Layer2 ServiceInstances (a bridge domain between LAN and WAN), there is no "l2protocol tunnel" option available. Performing a simple "l2protocol forwarding" Operation isn't possible because the LocalLoop carrier does not transport BPDUs.

I stumbled upon the Feature "l2protocol peer" command that i haven't seen before yet, but couldn't figure out what this exactly will do? Cisco says: "Configures transparent Layer 2 protocol peering on the interface for a specified layer 2 protocol." but what does "peering" in this case exactly mean? Are the Packets encapsulated in any form for transport, is this some sort o "rewriting" these packets or what will happen here on the protocol level? It would be nice if anybody can clarify this.

Answer 1

Definitely looks like a way to "escape" the slow protocols; specifying which slow protocol is sent to the local device, not over the tunnel.

This link explains:

l2protocol peer [protocol] - Configures transparent Layer 2 protocol peering on the interface for a specified layer 2 protocol

protocol —The protocol to be used. The options are: cdp, dtp, lacp, lldp, stp, and vtp .