Lsp Control Modes; Label Switch Routers - Extreme Networks BlackDiamond 6800 MPLS Installation And User Manual

Configuring the MPLS Module

LSP Control Modes

MPLS provides two LSP control modes:
• Independent
• Ordered
Using independent LSP control, each LSR makes independent decisions to bind labels
to FECs. By contrast, using ordered LSP control, the initial label for an LSP is always
assigned by the egress LSR for the associated FEC (either in response to a label request
message or by virtue of sending an unsolicited label mapping message).
More specifically, using ordered LSP control, an LSR only binds a label to a particular
FEC if it is the egress LSR for the FEC, or if it has already received a label binding for
the FEC from its next hop for the FEC. True to its name, the mode provides a more
controlled environment that yields benefits such as preventing loops and ensuring use
of consistent FECs throughout the network.
The Extreme MPLS implementation supports ordered LSP control, only.

Label Switch Routers

MPLS protocols are designed primarily for routed IP networks and are implemented by
Label Switch Routers (LSRs). The router where an LSP originates is called the ingress LSR,
while the router where an LSP terminates is called the egress LSR.
Ingress and egress LSRs are also referred to as Label Edge Routers (LERs). For any
particular LSP, a router is either an ingress LER, an intermediate LSR, or an egress LER.
However, a router may function as an LER for one LSP, while simultaneously function
as an intermediate LSR for another LSP.
Figure 3-2 illustrates the three types of LSRs.
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