Make-Before-Break - HP FlexNetwork HSR6600 Configuration Manual

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.
•
Forwarding adjacency—Considers the MPLS TE tunnel as a link that directly connects the
tunnel ingress node and the egress node, and advertises the link to the network through an IGP.
Every node in the network uses the MPLS TE tunnel during IGP route calculation.
As shown in
only the ingress node Router D to use the MPLS TE tunnel in the IGP route calculation. Router A
cannot use this tunnel to reach Router C. With forwarding adjacency enabled, Router A can learn this
MPLS TE tunnel and transfer traffic to Router C by forwarding the traffic to Router D.
Figure 26 IGP shortcut and forwarding adjacency diagram

Make-before-break

Make-before-break is a mechanism to change an MPLS TE tunnel with minimum data loss and
without using extra bandwidth.
In cases of tunnel reoptimization and automatic bandwidth adjustment, traffic forwarding is
interrupted if the existing CRLSP is removed before a new CRLSP is established. The
make-before-break mechanism ensures that the existing CRLSP is removed after the new CRLSP is
established and the traffic is switched to the new CRLSP. However, this wastes bandwidth resources
if some links on the old and new CRLSPs are the same. This is because you need to reserve
bandwidth on these links for the old and new CRLSPs separately. 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.
Figure 26, an MPLS TE tunnel exists from Router D to Router C. IGP shortcut enables
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