12
Configuring a static LSP
Overview
A static label switched path (LSP) is established by manually specifying the incoming label and
outgoing label on each node (ingress, transit, or egress node) of the forwarding path.
Static LSPs consume fewer resources, but they cannot automatically adapt to network topology
changes. Therefore, static LSPs are suitable for small and stable networks with simple topologies.
The ingress node of a static LSP performs the following operations:
1.
Determines an FEC for a packet according to the destination address.
2.
Adds the label for that FEC into the packet.
3.
Forwards the packet to the next hop or out of the outgoing interface.
A transit node swaps the label carried in a received packet with a label, and forwards the packet to
the next hop or out of the outgoing interface.
If PHP is not configured, an egress node pops the incoming label of a packet, and performs label
forwarding according to the inner label or IP forwarding.
Configuration guidelines
Follow these guidelines when you establish a static LSP:
•
On the ingress node, you must specify the outgoing label for the destination address (the FEC)
and the next hop or the outgoing interface.
•
On each transit node, you must specify the incoming label, the outgoing label, and the next hop
or the outgoing interface.
•
On the egress node, you must specify the incoming label.
•
You can associate a static LSP with an LDP LSP to simplify packet processing when the
following conditions are met:
{
Packets are forwarded over the static LSP and the LDP LSP to the destination.
{
The egress node of the static LSP is also the ingress node of the LDP LSP.
After receiving a packet with the specified incoming label, the egress node of the static LSP
swaps the label with the outgoing label for the LDP LSP. Then, the node forwards the packet to
the next hop.
To associate a static LSP with an LDP LSP, specify the incoming label and destination address
on the egress node of the static LSP.
•
The outgoing label specified on an LSR must be the same as the incoming label specified on
the directly connected downstream LSR.
Configuration prerequisites
Before you configure a static LSP, perform the following tasks:
•
Identify the ingress node, transit nodes, and egress node of the LSP.
•
Enable MPLS on all interfaces that participate in MPLS forwarding. For more information, see
"Configuring basic MPLS."
•
Make sure the ingress node has a route to the destination address of the LSP.
