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NE20E-S2 V800R010C10SPC500 Feature Description - MPLS 01

This is NE20E-S2 V800R010C10SPC500 Feature Description - MPLS
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Huawei uses machine translation combined with human proofreading to translate this document to different languages in order to help you better understand the content of this document. Note: Even the most advanced machine translation cannot match the quality of professional translators. Huawei shall not bear any responsibility for translation accuracy and it is recommended that you refer to the English document (a link for which has been provided).
TE FRR

TE FRR

Traffic engineering (TE) fast reroute (FRR) protects links and nodes on MPLS TE tunnels. If a link or node fails, TE FRR rapidly switches traffic to a backup path, minimizing traffic loss.

Background

A link or node failure in an MPLS TE tunnel triggers a primary/backup CR-LSP switchover. During the switchover, IGP routes converge to a backup CR-LSP, and CSPF recalculates a path over which the primary CR-LSP is reestablished. Traffic is dropped during this process.

TE FRR can be used to minimize traffic loss. TE FRR establishes a backup path that excludes faulty links or nodes. The backup path can rapidly take over traffic, minimizing traffic loss. In addition, the ingress attempts to reestablish the primary CR-LSP.

Benefits

TE FRR provides carrier-class local protection capabilities for MPLS TE CR-LSPs to improve network reliability.

Related Concepts

TE FRR works in either facility or one-to-one backup mode.

  • Facility backup

    Figure 4-19 illustrates facility backup networking.

    Figure 4-19 Schematic diagram for TE FRR in facility backup mode

    TE FRR working in facility backup mode establishes a bypass tunnel for each link or node that may fail on a primary tunnel. A bypass tunnel can protect traffic on multiple primary tunnels. TE FRR in facility backup mode is configured to establish a single bypass tunnel to protect primary tunnels. This mode is extensible, resource efficient, and easy to implement. Bypass tunnels must be manually planned and configured, which is time-consuming and laborious on a complex network.

  • One-to-one backup

    Figure 4-20 illustrates one-to-one backup networking.

    Figure 4-20 Schematic diagram for TE FRR in one-to-one backup mode

    TE FRR in one-to-one backup mode automatically creates a backup CR-LSP on each node along a primary CR-LSP to protects downstream links or nodes. This mode is easy to configure, eliminates manual network planning, and provides flexibility on a complex network. However, this mode has low extensibility, requires maintenance of the backup CR-LSP status on each node, and consumes more bandwidth than the facility backup mode.

Table 4-9 describes nodes and paths that support facility and one-to-one backup.

Table 4-9 Nodes and paths that support facility and one-to-one backup

Concept

Supported Protection Mode

Description

Primary CR-LSP

Both

A primary CR-LSP protected by a bypass CR-LSP.

Bypass CR-LSP

Facility backup

A bypass CR-LSP can protect multiple primary CR-LSPs. The bypass and primary CR-LSPs are established in different tunnels.

Detour LSP

One-to-one backup

Each detour LSP is automatically established to protect a primary CR-LSP. Detour LSPs and the primary CR-LSP are in the same tunnel.

Point of local repair (PLR)

Both

A PLR is the ingress of a bypass CR-LSP or a detour LSP. The PLR can be the ingress or a transit node but cannot be the egress of a primary CR-LSP.

Merge point (MP)

Both

An MP is the egress of a bypass CR-LSP or a detour LSP. It must reside on the primary CR-LSP but cannot be the ingress of the primary CR-LSP.

Detour merge point (DMP)

One-to-one backup

Two detour LSPs pass through the same path after they converge on the DMP.

Table 4-10 describes TE FRR protection functions implemented in facility and one-to-one backup modes.
Table 4-10 TE FRR protection functions implemented in facility and one-to-one backup modes

Classified By

Protection Function

Facility Backup

One-to-One Backup

Protected object

Node protection

A PLR and an MP are indirectly connected. A bypass CR-LSP protects a direct link to the PLR and nodes on the primary CR-LSP's path between the PLR and MP. Both the bypass CR-LSP in Figure 4-19 and the detour LSP 1 in Figure 4-20 provide node protection.

Link protection

A PLR and an MP are directly connected. A bypass CR-LSP only protects the direct link to the PLR. Detour LSP 2 in Figure 4-20 provides link protection.

Bandwidth to be reserved

Bandwidth protection

It is recommended that you configure the bypass CR-LSP to be smaller than or equal to the bandwidth of the primary CR-LSP according to the actual situation.

By default, a detour LSP has the same bandwidth as protected primary CR-LSP and provides bandwidth protection.

Non-bandwidth protection

A bypass CR-LSP without bandwidth assigned protects only the path over which the primary CR-LSP is established.

Not supported.

Implementation

Manual

A bypass CR-LSP is manually configured.

Not supported.

Automatic

Auto FRR-enabled nodes automatically establish bypass CR-LSPs. If an FRR-enabled primary CR-LSP passing through such a node and a backup path is available, the node automatically establishes an FRR bypass CR-LSP and binds it to the primary CR-LSP.

Nodes on a primary CR-LSP automatically establish detour LSPs.

NOTE:

A bypass CR-LSP working in facility backup mode supports a combination of protection types. For example, a bypass CR-LSP can implement manual, node, and bandwidth protection.

Implementation

Facility backup implementation

The process of implementing TE FRR in facility backup mode is as follows:

  1. The ingress establishes a primary CR-LSP.

    Figure 4-21 TE FRR local protection
    A primary CR-LSP is established in a way similar to that of an ordinary CR-LSP. The difference is that the ingress appends the following flags into the Session_Attribute object in a Path message.
    • "Local protection desired" flag: enables node or link protection.
    • "Label recording desired" flag: allows the message to record labels.
    • "SE style desired" flag: enables resource reservation in shared explicit (SE) style.
    • "Bandwidth protection desired" flag: enables bandwidth protection. This flag is added only if bandwidth protection needs to be provided.
  2. A PLR binds a bypass CR-LSP to the primary CR-LSP.

    Figure 4-22 Binding between bypass and primary CR-LSPs

    The process of searching for a suitable bypass CR-LSP is also called bypass CR-LSP binding. The primary CR-LSP only with the "local protection desired" flag can trigger a binding process. The binding must be complete before a primary/bypass CR-LSP switchover is performed. During the binding, the PLR must obtain information about the outbound interface of the bypass CR-LSP, next hop label forwarding entry (NHLFE), label switching router (LSR) ID of the MP, label allocated by the MP, and protection type.

    The PLR already obtains the next hop (NHOP) and next NHOP (NNHOP) of the primary CR-LSP. The PLR establishes a bypass CR-LSP to provide a specific type of protection based on the NHOP and NNHOP LSR IDs:
    • Link protection can be provided if the egress LSR ID of the bypass CR-LSP is the same as the NHOP LSR ID.
    • Node protection can be provided if the egress LSR ID of the bypass CR-LSP is the same as the NNHOP LSR ID.
    For example, in Figure 4-22, bypass CR-LSP 1 protects a link, and bypass CR-LSP 2 protects a node.

    If multiple bypass CR-LSPs are established, the PLR selects one with the highest priority. Protection types are prioritized in descending order: bandwidth protection, non- bandwidth protection, node protection, link protection, manual protection, and automatic protection. Both bypass CR-LSPs 1 and 2 shown in Figure 4-22 are manually configured to provide bandwidth protection. Bypass CR-LSP 1 that protects a link has a lower priority than bypass CR-LSP 2 that protects a node. In this situation, only bypass CR-LSP 2 can be bound to a primary CR-LSP. If bypass CR-LSP 1 protects bandwidth and bypass CR-LSP 2 does not, only bypass CR-LSP 1 can be bound to the primary CR-LSP.

    After a bypass CR-LSP is successfully bound to the primary CR-LSP, the NHLFE of the primary CR-LSP is recorded. The NHLFE contains the NHLFE index of the bypass CR-LSP and the inner label assigned by the MP. The inner label is used to forward traffic during FRR switching.

  3. The PLR detects faults.

    • In link protection, a data link layer protocol is used to detect and advertise faults. The speed of fault detection at the data link layer depends on link types.
    • In node protection, a data link layer protocol is used to detect link faults. If no link fault occurs, RSVP Hello detection or bidirectional forwarding detection (BFD) for RSVP is used to detect faults in protected nodes.
    If a link or node fault is detected, FRR switching is triggered immediately.
    NOTE:

    If node protection is enabled, only the link between the protected node and PLR is protected. The PLR cannot detect faults in the link between the protected node and MP.

  4. The PLR performs a traffic switchover.

    If a primary CR-LSP fails, the PLR switches both service traffic and RSVP messages to a detour LSP and advertises the switchover event upstream. The PLR pushes the inner and outer labels that the MP assigns for the primary and bypass CR-LSPs, respectively. The penultimate hop along the bypass CR-LSP removes the outer label from the packet and forwards the packet only with the inner label to the MP. The MP forwards the packet to the next hop along the primary CR-LSP.

    Figure 4-23 illustrates the process of forwarding a packet on nodes along the primary and bypass CR-LSPs before TE FRR switching is performed.

    Figure 4-23 Packet forwarding before TE FRR switching

    In Figure 4-23, the bypass CR-LSP provides node protection. If the link between LSRB and LSRC fails or LSRC fails, LSRB (PLR) swaps an inner label 1024 for an inner label 1022, pushes an outer label 34 into a packet, and forwards the packet along the bypass CR-LSP. After the packet arrives at LSRD, LSRD forwards the packet to LSRE at the next hop. Figure 4-24 illustrates the forwarding process after TE FRR switching is complete.

    Figure 4-24 Packet forwarding after TE FRR switching
  5. The ingress performs a traffic switchback.

    After TE FRR (either manual or auto FRR) switching is complete, the PLR (ingress) attempts to reestablish the primary CR-LSP using the make-before-break mechanism. Service traffic and RSVP messages switch from the bypass CR-LSP back to the successfully reestablished primary CR-LSP. The reestablished CR-LSP is called a modified CR-LSP. The original primary CR-LSP is only torn down after the modified CR-LSP is established successfully.

One-to-one backup implementation

The process of implementing TE FRR in one-to-one backup mode is as follows:

  1. The ingress establishes a primary CR-LSP.

    The process of establishing a primary CR-LSP in one-to-one backup is similar to that in the facility mode. The ingress appends the "local protection desired", "label recording desired", and "SE style desired" flags to the Session_Attribute object carried in a Path message.

  2. A PLR establishes a detour LSP.

    Figure 4-25 Detour LSP establishment and label swapping

    Except the egress, each node on the primary CR-LSP attempts to establish a detour LSP to protect a downstream link or node. Only qualified nodes can function as PLRs and establish detour LSPs over paths calculated using CSPF.

    Each PLR obtains NHOP information. A PLR establishes a detour LSP to provide a specific type of protection:
    • Link protection is provided if the MP LSR ID on a detour LSP is the same as the NHOP LSR ID. Detour LSP 2 in Figure 4-25 provides link protection.
    • Node protection is provided if the MP LSR ID on a detour LSP differs from the NHOP LSR ID when other nodes exist between the PLR and MP. Detour LSP 1 in Figure 4-25 provides node protection.
    If a PLR can establish detour LSPs that provide both link and node protection, the PLR only establishes a detour LSP that supports node protection.
  3. A PLR detects faults.

    • In link protection, a data link layer protocol is used to detect and advertise faults. The speed of fault detection at the data link layer depends on link types.

    • In node protection, a data link layer protocol is used to detect link faults. If no link fault occurs, RSVP Hello detection or BFD is used to detect faults in a protected node.

    If a link or node fault is detected, FRR switching is triggered immediately.

    NOTE:

    If node protection is enabled, only the link between the protected node and PLR is protected. The PLR cannot detect faults in the link between the protected node and MP.

  4. A PLR performs a traffic switchover.

    If a primary CR-LSP fails, the PLR switches both service traffic and RSVP messages to a detour LSP and advertises the switchover event upstream. In facility backup, a label stack contains two labels. In one-to-one backup, a label stack contains a single label.

    In Figure 4-25, a primary CR-LSP and two detour LSPs are established. If no faults occur, traffic passes through the primary CR-LSP based on labels. If a link between LSRB and LSRC fails, LSRB detects the link fault and switches traffic to detour LSP 2. LSRB swaps label 1024 for label 36 in a packet and sends the packet to LSRE. LSRE is the DMP of these two detour LSPs. On LSRE, detour LSPs 1 and 2 merge into one detour LSP (named detour LSP 1, for example). LSRE swaps label 36 for label 37 and sends the packet to LSRC. Detour LSP 1 overlaps the primary CR-LSP since LSRC. Therefore, LSRC uses a label for the primary CR-LSP and sends the packet to the egress LSRD.

  5. The ingress on the primary CR-LSP performs a traffic switchback.

    After performing a traffic switchover, the ingress on the primary CR-LSP attempts to reestablish a modified CR-LSP using the make-before-break mechanism. The ingress then switches service traffic and RSVP messages to the established modified CR-LSP and tears down the original primary CR-LSP.

Other Usage

When the TE FRR is in the FRR-in-use state, the interface sends RSVP messages without interface authentication TLV to a remote interface. Upon receipt of this message, the remote interface does not perform interface authentication in this situation. To enable authentication, the neighbor authentication mode can be configured.

TE FRR can be used to implement board removal protection. Board removal protection enables a PLR to retain information about the primary CR-LSP's outbound interface that resides on an interface board of the PLR. If the interface board is removed, the PLR rapidly switches MPLS TE traffic to a bypass CR-LSP or a detour LSP. After the interface board is re-installed, the PLR switches MPLS TE traffic back to the primary CR-LSP through the outbound interface. Board removal protection protects traffic on the primary CR-LSP's outbound interface of the PLR.

Without board removal protection, after an interface board on which a tunnel interface resides is removed from the PLR, CR-LSP information is lost on the PLR. To prevent CR-LSP information loss, ensure that the interface board to be removed does not have the following interfaces: primary CR-LSP's tunnel interface, bypass CR-LSP's tunnel interface, bypass CR-LSP's outbound interface, or detour LSP's outbound interface.

Configuring a TE tunnel interface on the PLR's IPU is recommended. If the interface board on which the primary CR-LSP's physical outbound interface resides is removed or fails, the PLR sets the outbound interface to the Stale state. The PLR's main control board retains information about each FRR-enabled primary CR-LSP that passes through the outbound interface. After the interface board is re-installed, the outbound interface becomes available again. Each primary CR-LSP is then automatically reestablished.

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Updated: 2019-01-02

Document ID: EDOC1100055471

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