Service Reachability; Carrier-Class Ethernet Infrastructure - Juniper M10i Application Note

Service Reachability

Once you assume that the control plane and the forwarding plane have reasonable scalability properties, the
next step is determining how far you can provision your VPLS-based services: Within one region of the country?
Nationwide? Internationally? Depending on the answer to this question, a single network frontier may need to be
trespassed to provide the service, so Inter-AS VPLS may be required.
As specified in RFC 4762:
Hierarchy can also be used to create a large-scale VPLS service within a single domain or a service that spans
multiple domains without requiring full mesh connectivity between all VPLS-capable devices. Two fully meshed
VPLS networks are connected together using a single LSP tunnel between the VPLS "border" devices. A single spoke
pseudowire per VPLS service is set up to connect the two domains together.
When more than two domains need to be connected, a full mesh of inter-domain spokes is created between border
PEs. Forwarding rules over this mesh are identical to the rules defined in Section 4.
This creates a three-tier hierarchical model that consists of a hub- and-spoke topology between MTU-s and PE-rs
devices, a full-mesh topology between PE-rs, and a full mesh of inter-domain spokes between border PE-rs devices.
BGP-based VPLS, on the other hand, has been designed to support Inter-AS service extension by defining several
options, which include redundancy (more details in section 3.5 of RFC 4761), and defining how efficient multicast
forwarding can also be extended in an Inter-AS scenario with VPLS (draft-ietf-l2vpn-vpls-mcast-01.txt).
So if you look at the previous dimensions of "scalability," you can conclude that BGP-based VPLS with point-to-
multipoint LSPs can be a better path for scalability compared with LDP-based H-VPLS.

Carrier-Class Ethernet Infrastructure

Ethernet has proven to be a key technology for the service provider's next-generation services, as it provides the
bandwidth and the cost point required for scalability and profitability. There are, however, several ways of using
Ethernet to provide services, and some have been described in this document. These different techniques do not
have the same properties, and not all of them can be considered carrier class.
Among these properties, we can find: scalability, flexibility, network efficiency, reliability, and operational complexity.
We have already analyzed the differences in terms of scalability between these solutions. In terms of flexibility, there
is probably not a big difference among all the VPLS-based technologies, so you could probably say that LDP VPLS,
H-VPLS, and BGP VPLS have similar properties in terms of flexibility with the exception of the ability to extend the
service through other networks, where clearly BGP VPLS has an advantage.
However, let´s analyze the other three carrier-class properties because they have a direct impact on the service
provider's costs:
• Network efficiency: A technology that does not use the network resources efficiently will result in additional
costs for the service provider, either because extra equipment is needed, or additional links, or it consumes
excess bandwidth. So, network efficiency has a clear impact on capital expenditures (CapEx), and probably on
operating expenditures (OpEx) as well.
• Reliability: The lack of reliability has a direct link with OpEx, so it is clearly a requirement for a carrier-class
infrastructure.
• Operational complexity: The more difficult a technology is to operate, either because it requires many
provisioning points, or many protocols to handle, or particular cases to deal with, the higher the operating
expense will be for the service provider.
Therefore, from the perspective of these three attributes, a real carrier-class technology should offer the service
provider the following: high network efficiency, high reliability, and low operational complexity. There are always
trade-offs and in many cases mutual dependencies exist among them, so increasing one might decrease the other.
Copyright © 2010, Juniper Networks, Inc.
10.3. Multi-domain VPLS Service
APPLICATION NOTE - Demystifying H-VPLS
7