MPLS local protection
Encyclopedia
MPLS
Fast Reroute (also called MPLS local restoration or MPLS local protection) is a local restoration network resiliency
mechanism. It is actually a feature of RSVP
Traffic Engineering
(RSVP-TE
). In MPLS local protection each LSP
passing through a facility is protected by a backup path which originates at the node immediately upstream to that facility.
This node which redirects the traffic onto the preset backup path is called the Point of Local Repair (PLR), and the node where a backup LSP merges with the primary LSP is called Merge Point (MP). This mechanism (local protection) provides faster recovery because the decision of recovery is strictly local. For comparison, when recovery mechanisms are employed at the IP
layer, restoration may take several seconds which is unacceptable for real-time applications (such as VoIP). In contrast, MPLS local protection meets the requirements of real-time applications with recovery times comparable to those of SONET
rings (< 50 ms).
, or LSP) from A to E via B and D. The traffic of customers connected to A and E will take this path in the normal operation. There is also a secondary path (LSP) from A to E via C. This path can be either pre-signaled or not. For the primary LSP, FRR (Fast ReRoute) is enabled. Once enabled, the other network elements on the LSP will know that FRR is enabled. Let's assume there is a break between D and E. D will immediately know this and it will inform B and A. For A to know that there is a failure between D and E, it takes a while. Since D gets to know immediately about the failure and FRR is enabled on the LSP, it uses the detour path D-C-E to get rid of the failure immediately and traffic will continue to flow along that path. This takes less than 50ms. Once the secondary LSP is up, traffic is switched to the secondary LSP and detour path is turned down.
Mpls
MPLS or Mpls can refer to:* Minneapolis, Minnesota, United States* Multiprotocol Label Switching, a data-carrying mechanism in computer networking...
Fast Reroute (also called MPLS local restoration or MPLS local protection) is a local restoration network resiliency
Resilience (network)
In computer networking: “Resilience is the ability to provide and maintain an acceptable level of service in the face of faults and challenges to normal operation.”These services include:* supporting distributed processing* supporting networked storage...
mechanism. It is actually a feature of RSVP
Resource Reservation Protocol
The Resource Reservation Protocol is a Transport Layer protocol designed to reserve resources across a network for an integrated services Internet. RSVP operates over an IPv4 or IPv6 Internet Layer and provides receiver-initiated setup of resource reservations for multicast or unicast data flows...
Traffic Engineering
Teletraffic engineering
Telecommunications traffic engineering, teletraffic engineering, or traffic engineering is the application of traffic engineering theory to telecommunications...
(RSVP-TE
RSVP-TE
Resource Reservation Protocol - Traffic Engineering is an extension of the resource reservation protocol for traffic engineering. It supports the reservation of resources across an IP network. Applications running on IP end systems can use RSVP to indicate to other nodes the nature of the packet...
). In MPLS local protection each LSP
Label Switched Path
In MPLS networking, a Label Switched Path is a path through an MPLS network, set up by a signaling protocol such as LDP, RSVP-TE, BGP or CR-LDP. The path is set up based on criteria in the forwarding equivalence class ....
passing through a facility is protected by a backup path which originates at the node immediately upstream to that facility.
This node which redirects the traffic onto the preset backup path is called the Point of Local Repair (PLR), and the node where a backup LSP merges with the primary LSP is called Merge Point (MP). This mechanism (local protection) provides faster recovery because the decision of recovery is strictly local. For comparison, when recovery mechanisms are employed at the IP
Internet Protocol
The Internet Protocol is the principal communications protocol used for relaying datagrams across an internetwork using the Internet Protocol Suite...
layer, restoration may take several seconds which is unacceptable for real-time applications (such as VoIP). In contrast, MPLS local protection meets the requirements of real-time applications with recovery times comparable to those of SONET
Synchronous optical networking
Synchronous Optical Networking and Synchronous Digital Hierarchy are standardized multiplexing protocols that transfer multiple digital bit streams over optical fiber using lasers or highly coherent light from light-emitting diodes . At low transmission rates data can also be transferred via an...
rings (< 50 ms).
Local protection approaches
There are two distinct approaches to local protection: (1) one-to-one local protection (detour) (2) many-to-one local protection (facility backup).One-to-one local protection
In one-to-one backup approach, the PLRs maintain separate backup paths for each LSP passing through a facility. The backup path terminates by merging back with the primary path at a node called the Merge Point (MP). In one-to-one backup approach, the MP can be any node downstream from the protected facility. Maintaining state information for backup paths protecting individual LSPs, as in the one-to-one approach, is a significant resource burden for the PLR. Moreover, periodic refresh messages sent by the PLR, in order to maintain each backup path, may become a network bottleneck.Many-to-one local protection
In many-to-one approach, a PLR maintains a single backup path to protect a set of primary LSPs traversing the triplet (PLR, facility, MP). Thus, fewer states need to be maintained and refreshed which results in a scalable solution. The many-to-one backup approach is also called facility backup. Note that in this approach, the MP should be the node immediately downstream to the facility.Example
In Fig.1 (right), there is a primary path (Label Switched PathLabel Switched Path
In MPLS networking, a Label Switched Path is a path through an MPLS network, set up by a signaling protocol such as LDP, RSVP-TE, BGP or CR-LDP. The path is set up based on criteria in the forwarding equivalence class ....
, or LSP) from A to E via B and D. The traffic of customers connected to A and E will take this path in the normal operation. There is also a secondary path (LSP) from A to E via C. This path can be either pre-signaled or not. For the primary LSP, FRR (Fast ReRoute) is enabled. Once enabled, the other network elements on the LSP will know that FRR is enabled. Let's assume there is a break between D and E. D will immediately know this and it will inform B and A. For A to know that there is a failure between D and E, it takes a while. Since D gets to know immediately about the failure and FRR is enabled on the LSP, it uses the detour path D-C-E to get rid of the failure immediately and traffic will continue to flow along that path. This takes less than 50ms. Once the secondary LSP is up, traffic is switched to the secondary LSP and detour path is turned down.