Mpls And Ip Routing - Extreme Networks BlackDiamond 6800 MPLS Installation And User Manual

6

MPLS and IP Routing

This chapter describes how MPLS and IP routing work together to forward information
on your network.
This chapter covers the following topics:
• Routing Using LSPs on page 6-2
• LSPs and IBGP Next Hops on page 6-5
• Optimized Forwarding of Non-MPLS IP Traffic on page 6-6
MPLS provides a great deal of flexibility for routing packets. Received IP unicast frames
can be transmitted over LSPs or routed normally. If a matching FEC exists for the
received packet, the packet is transmitted over an LSP that is associated with the FEC.
The packet is encapsulated using an MPLS shim header before being transmitted.
Received MPLS packets can be label switched or routed normally toward the
destination. Packets that are in the middle of an LSP are label switched. The incoming
label is swapped for a new outgoing label and the packet is transmitted to the next LSR.
For packets that have arrived at the end of an LSP (the egress end of the LSP), the shim
header is stripped or the label stack is popped, and the packets are routed to the
destination as normal IP packets.
Multicast routing is not supported.
An MPLS domain is generally defined to be an OSPF autonomous system (AS). You can
use MPLS to reach destinations outside of an OSPF AS.
MPLS Module Installation and User Guide 6-1