R3303-HP HSR6800 Routers MPLS Configuration Guide

Resource reservation style—Assigned to each LSP set up using RSVP-TE. During an RSVP session, the

receiver decides which reservation style can be used for this session and which LSPs can be used. The

following reservation styles are available:

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

among senders on the same session.

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

among them. SE is only used for make-before-break because multiple LSPs cannot be present on the

same session.

Make-before-break

Make-before-break is a mechanism to change MPLS TE tunnel attributes with minimum data loss and

without extra bandwidth.

Figure 15 Diagram for make-before-break

Figure 15 presents a scenario where a path Router A → Router B → Router C → Router D is established

with 30 Mbps reserved bandwidth between Router A and Router D. The remaining bandwidth is then 30

Mbps.

If 40 Mbps path bandwidth is requested, the remaining bandwidth of the Router A → Router B → Router

C → Router D path is inadequate. The problem cannot be addressed by selecting another path, Router

A → Router E → Router C → Router D, because the bandwidth of the Router C → Router D link is

inadequate.

To address the problem, you can use the make-before-break mechanism. It allows the new path to share

the bandwidth of the original path at the Router C → Router D link. Upon creation of the new path, traffic

is switched to the new path and the previous path is torn down. This helps avoid traffic interruption

effectively.

RSVP-TE messages

RSVP-TE uses RSVP messages with extensions. RSVP uses the following types of messages:

• Path messages—Transmitted along the path of data transmission downstream by each RSVP sender

to save path state information on each node along the path.

Resv messages—Sent by each receiver upstream towards senders to request resource reservation

and to create and maintain reservation state on each node along the reverse of data transmission

path.

• PathTear messages—Sent downstream to remove the path state and related reservation state on

each node along the path.

• ResvTear messages—Sent upstream to remove the reservation state on each node along the path.

• PathErr messages—Sent upstream to report Path message processing errors to senders. They do not

affect the state of the nodes along the path.