Make-Before-Break - HP MSR2000 Configuration Manual

tunnel can participate 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
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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, so every
node in the network uses the MPLS TE tunnel during IGP route calculation.
IGP shortcut and forwarding adjacency have the following differences:
After IGP shortcut is enabled on the ingress node, IGP shortcut does not advertise the MPLS TE
•
tunnel as a link through the IGP. Only the ingress node includes the MPLS TE tunnel in route
calculation.
After forwarding adjacency is enabled on the ingress node, the ingress node advertises the MPLS
•
TE tunnel as a link in the network through the IGP. All devices in the IGP network can use the MPLS
TE tunnel in their IGP route calculation.
Figure 21 IGP shortcut and forwarding adjacency diagram
As shown in
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 also know the existence of
the MPLS TE tunnel, so it can use this tunnel to transfer traffic to Router C by forwarding the traffic to
Router D.

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
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 wastes bandwidth resources if some links on the old and new
CRLSPs are the same. It is because you need to reserve bandwidth on these links for the old and new
Figure 21, an MPLS TE tunnel is present from Router D to Router C. IGP shortcut enables only
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