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NE20E-S2 V800R010C10SPC500 Feature Description - Network Reliability 01

This is NE20E-S2 V800R010C10SPC500 Feature Description - Network Reliability
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Association Between a VRRP Backup Group and a Route

Association Between a VRRP Backup Group and a Route

Background

To improve device reliability, two user gateways working in master/backup mode are connected to a network, and VRRP is enabled on these gateways to determine their master/backup status. If a VRRP backup group has been configured and an uplink route to a network becomes unreachable, access-side users still use the VRRP backup group to forward traffic along the uplink route, which causes user traffic loss.

Association between a VRRP backup group and a route can prevent user traffic loss. A VRRP backup group can be configured to track the uplink route to a network. If the route is withdrawn or becomes inactive, the route management (RM) module notifies the VRRP backup group of the change. After receiving the notification, the VRRP backup group changes its master device's VRRP priority and performs a master/backup switchover. This process ensures that user traffic can be forwarded along a properly functioning link.

Implementation

A VRRP backup group can be associated with an uplink route to a network to determine whether the route is reachable. If the uplink route is withdrawn or becomes inactive after the uplink goes Down or the network topology changes, hosts on a local area network (LAN) fail to access the external network through gateways. The RM module notifies the VRRP backup group of the route status change. The VRRP priority of the master device decreases by a specified value. A backup device with a priority higher than others preempts the Master state and takes over traffic. This process ensures communication continuity between these hosts and the external network. After the uplink recovers, the RM module instructs the VRRP backup group to restore the master device's VRRP priority.

As shown in Figure 5-25, a VRRP backup group is configured on Device A (master) and Device B (backup), with Device A forwarding user traffic. The VRRP backup group on Device A is associated with the route 100.1.2.0/24.

When the uplink from Device A to Device C goes Down, the route 100.1.2.0/24 becomes unreachable and Device A's VRRP priority decreases. Because Device A's reduced VRRP priority is lower than Device B's VRRP priority, Device B preempts the Master state and takes over traffic, which prevents user traffic loss.

Figure 5-25 Association between a VRRP backup group and a route

VRRP device configurations are as follows:

  • Device A's VRRP priority is 120.
  • Device B supports immediate preemption and its VRRP priority retains the default value 100.
  • The VRRP backup group on Device A is associated with the route 100.1.2.0/24. If the RM module informs Device A that the route 100.1.2.0/24 is unreachable, Device A's VRRP priority decreases by 40.

The implementation process is as follows:

  1. In normal circumstances, Device A periodically sends VRRP Advertisement packets to inform Device B that it is working properly.
  2. When the uplink between Device A and Device C goes Down, the route 100.1.2.0/24 becomes unreachable. The RM module notifies the VRRP backup group on Device A of the route status change. After Device A receives the notification, its VRRP priority decreases to 80 (120 - 40). Because the VRRP priority of Device B is higher than that of Device A, Device B preempts the Master state and sends gratuitous ARP packets to update address entries on Device E.
  3. When the faulty link recovers, the route 100.1.2.0/24 is reachable. Device A restores its VRRP priority to 120 (80 + 40), preempts the Master state, and sends VRRP Advertisement packets and gratuitous ARP packets. After Device B receives the Advertisement packets and determines that its priority is lower than that of Device A, Device B returns to the Backup state.

  4. Device A in the Master state forwards user traffic, and Device B remains in the Backup state.

The preceding process shows that the VRRP backup group performs a master/backup switchover if the uplink route is unreachable.

Benefits

Association between a VRRP backup group and a route helps implement a master/backup VRRP switchover when an uplink route to a network is unreachable. The association also ensures that the VRRP backup group performs a traffic switchback and minimizes traffic downtime.

Compared with the association between a VRRP backup group and the interface status, the association detects both direct uplink interface faults and faults of links and devices when uplink traffic passing through multiple devices.

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Updated: 2019-01-02

Document ID: EDOC1100055473

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