R211x-HP Flexfabric 11900 MPLS Configuration Guide

Dynamic CRLSP establishment

Dynamic CRLSPs are dynamically established through a label distribution protocol (such as RSVP-TE). The

label distribution protocol advertises labels to establish CRLSPs and reserves bandwidth resources on

each node along the calculated path.

Dynamic CRLSPs adapt to network changes and support CRLSP backup, but they require complicated

configurations.

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 creating a static route that reaches the destination through the tunnel

interface.

This is the easiest way to implement MPLS TE tunnel forwarding. However, 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.

Make-before-break

Make-before-break is a mechanism to change an MPLS TE tunnel with minimum data loss and without

using extra bandwidth.

Traffic forwarding is interrupted if the existing CRLSP is removed before a new CRLSP is established. The

make-before-break mechanism makes sure that the existing CRLSP is removed after the new CRLSP is

established and the traffic is switched to the new CRLSP. However, this might waste bandwidth resources

if some links on the old and new CRLSPs are the same, because you need to reserve bandwidth on these

links for both the old and new CRLSPs. The make-before-break mechanism uses the SE resource

reservation style to address this problem.

The resource reservation style refers to the style in which RSVP-TE reserves bandwidth resources during

CRLSP establishment. The resource reservation style used by an MPLS TE tunnel is determined by the

ingress node, and is advertised to other nodes through RSVP.

The device supports the following resource reservation styles:

• FF—Fixed-filter, where resources are reserved for individual senders and cannot be shared among

senders on the same session.

• SE—Shared-explicit, where resources are reserved for senders on the same session and shared

among them. SE is mainly used for make-before-break.