MPLS Error Detection

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LDP and CR-LDP are protocols that contain an error message type-length value (TLV) to report link and node errors. However, there are two main disadvantages to this method. First, it takes time to send the error message. Second, since LDP is a connection-oriented message, the notification message might never arrive if the link is down.

An alternative approach to error detection is to use the heartbeat method that is found at the foundation of the RSVP-TE protocol. RSVP has features that make it a good alternative for an error message model. RSVP is a soft-state protocol that requires refreshing-in other words, if the link is not refreshed, that link is torn down. No error messages are required, and rapid recovery (rapid reroute) is possible if there is a preprovisioned path. If RSVP-TE is already used as a signaling protocol, the additional overhead required for rapid recovery is insignificant.

RRR

Rapid Reroute (RRR) is a process in which a link failure can be detected without the need for signaling. Because RSVP-TE offers soft-state signaling, it can handle a rapid reroute. Many vendors are using the RSVP-TE for rapid recovery of tunnels and calls, but in so doing, other MPLS options are restricted (for example, labels are allocated per switch, not per interface). Another restriction of RSVP-TE is that it must also be used for an across-the-board signaling protocol.

RSVP-TE Protection

In RSVP-TE, two methods are used to protect the network: link protection and node protection.

In link protection, a single link is protected with a preprovisioned backup link. If there is a failure in the link, the switches will open the preprovisioned path (see Figure 4.10).

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Figure 4.10: RSVP-TE with Link Protection

In a node failure, an entire node or switch could fail; thus, all links attached to that node could fail. With node protection, a preprovisioned tunnel is provided around the failed node (see Figure 4.11).

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Figure 4.11: RSVP-TE with Node Protection



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Rick Gallagher's MPLS Training Guide. Building Multi-Protocol Label Switching Networks
Rick Gallahers MPLS Training Guide: Building Multi Protocol Label Switching Networks
ISBN: 1932266003
EAN: 2147483647
Year: 2003
Pages: 138

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