H3C Technologies H3C S12500-X Series Switches - Manual (Page 56)

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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 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. 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.
Policy-based routing
You can configure PBR on the ingress interface of traffic to direct the traffic that matches an ACL to the
MPLS TE tunnel interface.
PBR can match the traffic to be forwarded on the tunnel not only by destination IP address, but also by
source IP address, protocol type, and other criteria. Compared with static routing, PBR is more flexible
but requires more complicated configuration.
For more information about policy-based 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.