Routing Protocols Configuration Guide for the SmartEdge OS ...

SmartEdge Routing
Layer 2 Virtual Private Network
Layer 2 Virtual Private Networks (L2VPNs) customer edge (CE) routers send L2 traffic to provider edge
(PE) routers over L2 circuits configured between the PE and the CE routers. An L2 circuit can be either an
Ethernet port, an 802.1Q virtual LAN (VLAN), a Frame Relay permanent virtual circuit (PVC), or an
Asynchronous Transfer Mode (ATM) PVC.
An L2VPN is configured on PE routers and is used to cross-connect a local L2 circuit with a corresponding
remote L2 circuit through an LSP tunnel that crosses the network backbone.
Label Distribution Protocol
LDP enables dynamic label allocation and distribution in an MPLS network. An LSR enabled with LDP
can establish LSPs to other LSRs in the network. LDP creates label bindings by assigning labels to
connected routers and by advertising the bindings to neighbors. LDP also assigns labels to label bindings
learned from neighbors, and readvertises the binding to other neighbors. When an LSR advertises a label
binding for a route, the LSR is advertising the availability of an LSP to the destination of that route. LDP
can learn several LSPs from different neighbors for the same route. In this case, LDP activates only the path
selected by the underlying IGP. For this reason, LDP must work together with an IGP, such as the IS-IS or
OSPF protocol.
Virtual Private LAN Services
VPLS enables networks at separate geographical locations to communicate with each other across a wide
area network (WAN) as if they were directly attached to each other in a LAN. The WAN becomes
transparent, which is achieved by creating VPLS pseudo-wires.
A pseudo-wire is a mechanism that emulates the attributes and function of Ethernet connectivity over a
WAN. Any required switching functionality or service translation is outside the scope of the pseudo-wire
and of the transport network. Pseudo-wires are carried over MPLS tunnels on the network.
MPLS signaling protocols are used to automatically provision a service on a pseudo-wire end-to-end, so
you can provision a pseudo-wire by pointing to its two endpoints, and MPLS automatically negotiates the
path.
Protocol Distances
When determining a single optimal route among multiple routes within a single routing protocol, the
SmartEdge OS selects the route that has the shortest distance. When deciding a best path among routes
originating from multiple protocols, the system uses a more complex methodology. The SmartEdge routing
table stores direct, static, external BGP (eBGP), OSPF, IS-IS, RIP, and internal BGP (iBGP) routes.
1-6 Routing Protocols Configuration Guide