H3C Technologies H3C S6800 Series Switches - Manual (Page 68)

55
higher than the holding priority of the existing tunnel. Both setup and holding priorities are in the
range of 0 to 7. A smaller value indicates a higher priority.
To avoid flapping caused by improper preemptions, the setup priority of a tunnel must not be
higher than its holding priority, namely, the setup priority value must be equal to or greater than
the holding priority value.
• Explicit path
Explicit path specifies the nodes to pass and the nodes to not pass for a tunnel.
Explicit paths include the following types:
{
Strict explicit path—Among the nodes that the path must traverse, a node and its previous hop
must be connected directly.
{
Loose explicit path—Among the nodes that the path must traverse, a node and its previous hop
can be connected indirectly.
Strict explicit path precisely specifies the path that an MPLS TE tunnel must traverse. Loose explicit
path vaguely specifies the path that an MPLS TE tunnel must traverse. Strict explicit path and loose
explicit path can be used together to specify that some nodes are directly connected and some
nodes have other nodes in between.
Setting up a CRLSP through RSVP-TE
After calculating a path by using CSPF, MPLS TE uses a label distribution protocol to set up the CRLSP and
reserves resources on each node of the path.
The device supports the label distribution protocol of RSVP-TE for MPLS TE. Resource Reservation Protocol
(RSVP) reserves resources on each node along a path. Extended RSVP can support MPLS label
distribution and allow resource reservation information to be transmitted with label bindings. This
extended RSVP is called RSVP-TE.
For more information about RSVP, see "
Configuring RSVP ."
Traffic forwarding
After an MPLS TE tunnel is established, traffic is not forwarded on the tunnel automatically. You must
direct the traffic to the tunnel by using one of the following methods.
Static routing
You can direct traffic to an MPLS TE tunnel by creating a static route that reaches the destination through
the tunnel interface. This is the easiest way to implement MPLS TE tunnel forwarding. When the traffic to
multiple networks is to be forwarded through the MPLS TE tunnel, you must configure multiple static routes,
which are complicated to configure and difficult to maintain.
For more information about static routing, see Layer 3—IP Routing Configuration Guide.
Automatic route advertisement
You can also configure automatic route advertisement to forward traffic through an MPLS TE tunnel.
Automatic route advertisement distributes the MPLS TE tunnel to the IGP (OSPF or IS-IS), so the MPLS TE
tunnel can participate in IGP routing calculation. Automatic route advertisement is easy to configure and
maintain.
Automatic route advertisement can be implemented by using the following methods:
• IGP shortcut—Also known as AutoRoute Announce. It considers the MPLS TE tunnel as a link that
directly connects the tunnel ingress node and the egress node. Only the ingress node uses the MPLS
TE tunnel during IGP route calculation.