MPLS L2VPN Types
- Pseudowires
- VPLS
- EVPN
There are differences in the way MAC addresses are learnt.
In VPLS, MAC addresses are learnt in the data plane.
In EVPN, MAC addresses are learnt in the control plane (using BGP). Less resources used, more effective than VPLS
Service Provider acts as a
- virtual wire
- virtual switch
There are multiple ways of creating both styles of Layer 2 VPN.
To generate Transport Label, IGP + BGP + LDP/RSVP
To generate a VPN Label (customer specific), another signalling protocol required
- BGP
- LDP
Pseduowires
Psuedowires: Point to Point Layer 2 VPN across a Service Provider network
Attachment Circuits (customer connections at either end)
One Pseudowire for each VLAN or all VLANs in a single pseudowire.
No MAC address learning needed over a single wire (on the PE devices). CE devices use ARP for learning the remote MACs.
PE devices simply forward with out any changes to the frame
Pseduowire use case in a Wholesaler Network
Data Center Interconnect - Pseudowires can be used for DCI
When a customer needs two sites to appear as one!
Two options to signal a Pseudowire:
-
BGP
-
LDP
Both options are equally popular and commonly used.
Labelstack of a Pseudowire
Original L2-L7 encapsulated by Control Word + VPN Label + Transport Label + Service Provider Ethernet Header
What is Control Word?
it is like CRC or flow control. Was required when other L2 technologies were used like ATM, Frame Relay (instead of Ethernet)
Control Word is optional.
SP Ethernet Header + Transport Label + VPN Label + Control Word + Original L2-L7 frame
BGP-signalled pseudowires - Kompella circuits (Kireeti Kompella) (l2vpn)
LDP-signalled pseudowire - Martini circuits (Luca Martini) (l2circuit)
Other alternative terms
VPWS - Virtual Private Wire Service
Metro Ethernet Forum (MEF)
-
E-Line single point to point pseudo wire
-
E-Tree multipoint pseudowires, point to multipoint Hub and Spoke
Circuit Cross Connect (CCC)
Third method of signalling pseudowires, to generate VPN label Created by Juniper before Kompella/Martini circuits Considered legacy nowadays, not recommended
One Pseudowire is mapped to two unique RSVP LSPs, one in each direction
CCC can also be used for encapsulation, not just for signalling! Be aware of the context!
With VPLS, PE devices start learning the MAC addresses, though we are building the pseudowires with VPLS.
L2VPN, L2Circuit, VPLS : all three are pseudowires
With first two options, PE does not learn MAC address
With VPLS, we will have an Instance and a table is maintained.
VPLS
SP acts as a distributed switch, a series of pseudowires (BGP/LDP signalled)
PE router learns MAC addresses
Unknown MACs are flooded
IRB can be placed inside a VPLS as the gateway out of the subnet, to connect to internet (a new service).
We can use BGP, LDP, or FEC 129 to create psuedowires for a VPLS.
In VPLS, customer routers form adjacencies directly. Service provider does not learn customer routes.
PE only learns the MAC addresses of the CE’s WAN facing ports
Use cases for VPLS - Wholesale, Data Center, Distributed Firewalls
MAC addresses are learned in the data plane, by flood and learn
VRRP is required for redundancy (traffic might have to traverse the entire VPLS domain just to ge to the active IRB)
Multihomed linked can not run in active/active (only one attachment circuit can be live, others must be shut down)
EVPN
EVPN also offer a distributed switch
MACs are now advertised in BGP
Old MACs can be withdrawn
MAC moves are advertised immediately
Multihomed links can be active/active. No need for Spanning Tree.
Remote PEs can automatically load balance
All PEs can host an active IRB (no need of VRRP, no need to travel across SP network, just to break out of the subnet)
Use cases: same as VPLS, but more popular in DC.
We can run all these VPN types on one physical customer-facing interface using encapsulation flexible-ethernet-services statement in Junos.
Each logical unit on a single physical interface can have different services, for example:
- Regular IPv4
- BGP signalled VPLS
- Untagged Layer 2
- VLAN tagged Layer 2
- BGP signalled Layer 2 VPN
- LDP signalled Layer 2 Circuit
- LDP singalled VPLS
