While both AToM and EoM are Point-to-Point Layer 2 MPLS Protocols, and L2TP is NOT related to MPLS (but a Layer 2 Tunneling Protocol all the same), VPLS is meant to be a Point-to-Multipoint or Multipoint-to-Multipoint Protocol to extend L2 across the MPLS.
Some Terminology and random points on VPLS
TLS – In VPLS terms this can mean “Transparent LAN Service” whereas when you see TLS you might immediately think of “Transport Layer Security” and TLS Handshakes
It connects using Ethernet (like our friend EoM), however unlike a point-to-point EoM Tunnel VPLS is a collection of those Tunnels, and can make switching decisions based on the best path to the destination gathered from this information.
Q in Q – Wanted to take a moment to trash Q in Q Tunneling with Service Providers as its described, as it only scales to 4096 available VLANs for customer use so its scalability hits a ceiling fast depending on the ISP size, and the Service Provider also needs to worry about STP (Spanning-Tree) coming into play WITHIN its own Provider Network!
No thank you to STP within a Provider Network!
VPLS takes that VLAN / Trunking information and Transports it through the Provider Network, and devices geographically separated will actually perform STP calculations for those remote sites, in regards to which ports are FWD / BLK across the Provider Network.
The Provider Edge is really the key to AToM, EoM, or VPLS networks doing their magic as that is where the configuration is setup and then the traffic is just transported through the network without further configuration!
That is a really big point for MPLS, the Provider Network really just Label Switches whatever traffic it gets, the only configs done are on the PE’s to make things work.
There are two different ways the VPLS is configured per Cisco
BGP-VPLS (RFC 4761) – An Advanced BGP VPLS configuration I am not aware of.
LDP-VPLS (RFC 4762) – Targeted LDP Session, this is what the CCIE would expect you to know as the VPLS deployment type.
To conclude this, I want to put into perspective what makes VPLS cool
The Provider Network acts like one giant Layer 2 Bridge, that performs the same functions a LAN Switch would perform such as “Learning / Forwarding / Flooding / Filtering / Aging” of MAC Addresses and Layer 2 information.
This is possible because of the mechanism that drives VPLS called VSI or Virtual Switching Instance, which is equivalent to VRF’s allowing for Layer 3 VPN to work through the Layer 3 IP MPLS Network.
IPv6 who? Why do we need 1.6 billion IP Addresses again?
That will wrap up my VPLS ranting as that about covers the topic to the extent I am happy to know it, I am basically just wanting to get a good understanding of these circuit types and terminology to work with providers, not necessarily to work for one.
Until next time!