No relevant resource is found in the selected language.

This site uses cookies. By continuing to browse the site you are agreeing to our use of cookies. Read our privacy policy>Search

Reminder

To have a better experience, please upgrade your IE browser.

upgrade

ME60 V800R010C10SPC500 Feature Description - WAN Access 01

This is ME60 V800R010C10SPC500 Feature Description - WAN Access

Rate and give feedback:
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).
OSPFv3 Auto FRR

OSPFv3 Auto FRR

OSPFv3 Auto Fast Reroute (FRR) is dynamic IP FRR in which a device pre-computes alternate next hops and stores them in the IP routing table. If a primary link fails, the device switches the traffic to a backup link.

OSPFv3 Auto FRR complies with standard protocols. With OSPFv3 Auto FRR, devices can switch traffic from a faulty primary link to a backup link, protecting against a link or node failure.

Background

As networks develop, voice over IP (VoIP) and online video services pose higher requirements for real-time transmission. Nevertheless, if a primary link fails, OSPFv3-enabled devices need to perform multiple operations, including detecting the fault, updating the link-state advertisement (LSA), flooding the LSA, calculating routes, and delivering forward information base (FIB) entries before switching traffic to a new link. This process takes a much longer time, the minimum delay to which users are sensitive. As a result, the requirements for real-time transmission cannot be met.

Principles

With OSPFv3 IP FRR, a device uses the loop-free alternate (LFA) algorithm to compute the next hop of a backup link and stores the next hop together with the primary link in the forwarding table. If the primary link fails, the device switches the traffic to the backup link before routes are converged on the control plane. This mechanism keeps the traffic interruption duration and minimizes the impacts. The ME60 supports OSPFv3 Auto FRR.

A device uses shortest path first (SPF) algorithm to calculate the shortest path from each neighbor that can provide a backup link to the destination node. The device then uses the inequalities defined in standard protocols and the LFA algorithm to calculate the next hop of the loop-free backup link that has the smallest cost of the available shortest paths.

An OSPFv3 Auto FRR policy is used to filter alternate next hops. Only the alternate next hops that match the filtering rules of the policy can be added to the IP routing table. Users can configure a desired OSPF IP FRR policy to filter alternate next hops.

If a Bidirectional Forwarding Detection (BFD) session is bound to OSPFv3 Auto FRR, the BFD session goes Down if BFD detects a link fault. If the BFD session goes Down, OSPFv3 Auto FRR is triggered on the interface to switch traffic from the faulty link to the backup link, which minimizes the loss of traffic.

Usage Scenario

OSPFv3 Auto FRR guarantees protection against either a link failure or a node-and-link failure. Distance_opt (X,Y) indicates the shortest path between node X and node Y.
  • Link protection: Link protection takes effect when the traffic to be protected flows along a specified link and the link costs meet the inequality: Distance_opt (N, D) < Distance_opt (N, S) + Distance_opt (S, D).
    • S: source node
    • N: node along a backup link
    • D: destination node

    On the network shown in Figure 7-3, traffic flows from Device S to Device D. The link cost satisfies the link protection inequality. If the primary link (Device S -> Device E -> Device D) fails, Device S switches the traffic to the backup link (Device S -> Device N -> Device E -> Device D), keeping the traffic interruption duration.

    Figure 7-3 Networking for OSPFv3 Auto FRR link protection
  • Link-and-node protection: Figure 7-4 shows a networking for link-and-node protection. The link-and-node protection takes precedence over the link protection.

    Link-and-node protection must satisfy the following conditions:

    • The link cost must satisfy the inequality: Distance_opt (N, D) < Distance_opt (N, S) + Distance_opt (S, D).
    • The interface cost of the Device must satisfy the inequality: Distance_opt (N, D) < Distance_opt (N, E) + Distance_opt (E, D).

      E: faulty node

      N: node on the backup link

      D: destination node

      Figure 7-4 Networking for OSPFv3 Auto FRR link-and-node protection

OSPFv3 FRR in a Multi-Source Routing Scenario

OSPFv3 LFA FRR uses the SPF algorithm to calculate the shortest path from each neighbor (root node) that provides a backup link to the destination node and store the node-based backup next hop, which applies to single-source routing scenarios. As networks are increasingly diversified, two ABRs or ASBRs are deployed to improve network reliability. In this case, OSPFv3 FRR in a multi-source routing scenario is needed.

NOTE:
In a multi-source routing scenario, OSPFv3 FRR is implemented by calculating the Type 3 LSAs advertised by ABRs of an area for intra-area, inter-area, ASE routing. Inter-area routing is used as an example to describe how OSPFv3 FRR in a multi-source routing scenario works.
Figure 7-5 OSPFv3 FRR in a multi-route source scenario

In Figure 7-5, Device B and Device C function as ABRs to forward area 0 and area 1 routes. Device E advertises an intra-area route. Upon receipt of the route, Device B and Device C translate it to a Type 3 LSA and flood the LSA to area 0. After OSPFv3 FRR is enabled on Device A, Device A considers Device B and Device C as its neighbors. Without a fixed neighbor as the root node, Device A fails to calculate FRR backup next hop. To address this problem, a virtual node is simulated between Device B and Device C and used as the root node of Device A, and Device A uses the LFA algorithm to calculate the backup next hop. This solution converts multi-source routing into single-source routing.

For example, both Device B and Device C advertise the 2001:DB8:1::1/64 route. After Device A receives the route, it fails to calculate a backup next hop for the route due to a lack of a fixed root node. To address this problem, a virtual node is simulated between Device B and Device C and used as the root node of Device A. The cost of the Device B-virtual node link is 0, and the cost of the Device C-virtual node link is 5. The cost of the virtual node-Device B or Device C link is the maximum value (65535). If the virtual node advertises the 2001:DB8:1::1/64 route, it will use the smaller cost of the routes advertised by Device B and Device C as the cost of the route. Device A is configured to consider Device B and Device C as invalid sources of the 2001:DB8:1::1/64 route and use the LFA algorithm to calculate the backup next hop for the route, with the virtual node as the root node.

Translation
Download
Updated: 2019-01-04

Document ID: EDOC1100059473

Views: 17559

Downloads: 10

Average rating:
This Document Applies to these Products

Related Version

Related Documents

Share
Previous Next