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

NE40E V800R010C10SPC500 Feature Description - Network Reliability 01

This is NE40E V800R010C10SPC500 Feature Description - Network Reliability
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).
BFD for VRRP

BFD for VRRP

Background

Devices in a VRRP backup group exchange VRRP Advertisement packets to negotiate the master/backup status and implement backup. If the link between devices in a VRRP backup group fails, VRRP Advertisement packets cannot be exchanged to negotiate the master/backup status. A backup device attempts to preempt the Master state after a period three times provided that; if the time interval at which VRRP Advertisement packets are broadcast. During this period, user traffic is still forwarded to the master device, which results in user traffic loss.

Bidirectional Forwarding Detection (BFD) can rapidly detect faults in links or IP routes. BFD for VRRP enables a master/backup VRRP switchover to be completed within 1 second, preventing user traffic loss. A BFD session is established between the master and backup devices in a VRRP backup group and is bound to the VRRP backup group. BFD immediately detects communication faults in the VRRP backup group and instructs the VRRP backup group to perform a master/backup switchover, minimizing service interruptions.

VRRP and BFD Association Modes

The following table describes VRRP and BFD association modes.

Table 2-8 VRRP and BFD association modes

Association Mode

Usage Scenario

Type of Associated BFD Session

Impact Mode

BFD Support

Association between a VRRP backup group and a common BFD session

A backup device monitors the status of the master device in a VRRP backup group. A common BFD session is used to monitor the link between the master and backup devices.

Static BFD sessions or static BFD sessions with automatically negotiated discriminators

If the BFD session detects a fault and goes Down, the BFD module notifies the VRRP backup group of the status change. After receiving the notification, the VRRP backup group changes VRRP priorities of devices and determines whether to perform a master/backup VRRP switchover.

VRRP devices must be enabled with BFD.

Association between a VRRP backup group and link and peer BFD sessions

The master and backup devices monitor the link and peer BFD sessions. A link BFD session is established between the master and backup devices. A peer BFD session is established between a downstream switch and each VRRP device. BFD helps the VRRP backup group detect faults in the link between a VRRP device and the downstream switch.

Static BFD sessions or static BFD sessions with automatically negotiated discriminators

If the link or peer BFD session goes Down, BFD notifies the VRRP backup group of the fault. After receiving the notification, the VRRP backup group immediately performs a master/backup VRRP switchover.

VRRP devices and the downstream switch must be enabled with BFD.

Association Between a VRRP Backup Group and a Common BFD Session

As shown in Figure 2-24, a BFD session is established between Device A (master) and Device B (backup) and is bound to a VRRP backup group. If BFD detects a fault on the link between Device B and Device A, the BFD module notifies the VRRP module of the status change. After receiving the notification, the VRRP module performs a master/backup VRRP switchover.

Figure 2-24 Association between a VRRP backup group and a common BFD session

VRRP device configurations are as follows:

  • Device A supports delayed preemption and its VRRP priority is 120.
  • Device B supports immediate preemption and its VRRP priority retains the default value 100.
  • A VRRP backup group is configured on Device B to monitor a common BFD session. If BFD detects a fault and the BFD session goes Down, Device B increases its VRRP priority by 40.

The implementation process is as follows:

  1. Device A periodically sends VRRP Advertisement packets to inform Device B that it is working properly. Device B monitors the status of Device A and the BFD session.
  2. If BFD detects a fault, the BFD session goes Down. BFD notifies the VRRP module of the status change. Device B increases its VRRP priority value to 140 (increased by 40), higher than Device A's VRRP priority. Device B preempts the Master state and sends gratuitous ARP packets to update address entries on Device E.
  3. After the fault is rectified, the BFD session goes Up.

    Device B restores a priority of 100. Device B retains the Master state and still sends VRRP Advertisement packets to Device A.

    After receiving the packets, Device A checks that the VRRP priority carried in the packets is lower than the local VRRP priority and waits a specified period before preempting the Master state. After restoring the Master state, Device A sends a VRRP Advertisement packet and a gratuitous ARP packet.

    After receiving the VRRP Advertisement packet that carries a priority higher than the local priority, Device B enters 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 BFD for VRRP is different from VRRP. After BFD for VRRP is deployed and a fault occurs, a backup device immediately preempts the Master state without waiting a period three times provided that; if the time interval at which VRRP Advertisement packets are broadcast. A master/backup VRRP switchover can be implemented in milliseconds.

Association Between a VRRP Backup Group and Link and Peer BFD Sessions

As shown in Figure 2-25, the master and backup devices monitor the status of link and peer BFD sessions to identify local or remote faults.

Device A and Device B run VRRP. A peer BFD session is established between Device A and Device B to detect link and device failures. Link BFD sessions are established between Device A and Device E and between Device B and Device E to detect link and device failures. After Device B detects that the peer BFD session goes Down and Link2 BFD session goes Up, Device B's VRRP status changes from Backup to Master, and Device B takes over.

Figure 2-25 Association between a VRRP backup group and link and peer BFD sessions

VRRP device configurations are as follows:

  • Device A and Device B run VRRP.
  • A peer BFD session is established between Device A and Device B to detect link and device failures.
  • Link1 and Link2 BFD sessions are established between Device E and Device A and between Device E and Device B, respectively.

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. Device A monitors the BFD session status. Device B monitors the status of Device A and the BFD session.
  2. The BFD session goes Down if BFD detects either of the following faults:
    • Link1 or Device E fails. Link1 BFD session and the peer BFD session go Down. Link2 BFD session is Up.

      Device A's VRRP status directly becomes Initialize.

      Device B's VRRP status directly becomes Master.

    • Device A fails. Link1 BFD session and the peer BFD session go Down. Link2 BFD session is Up. Device B's VRRP status becomes Master.

  3. After the fault is rectified, the BFD sessions go Up, and Device A and Device B restore their VRRP status.
NOTE:

A Link2 fault does not affect Device A's VRRP status, and Device A continues to forward upstream traffic. However, Device B's VRRP status becomes Master if both the peer BFD session and Link2 BFD session go Down, and Device B detects the peer BFD session status change before detecting the Link2 BFD session status change. After Device B detects the Link2 BFD session status change, Device B's VRRP status becomes Initialize.

Figure 2-26 shows the state machine for the association between a VRRP backup group and link and peer BFD sessions.

Figure 2-26 State machine for the association between a VRRP backup group and link and peer BFD sessions

The preceding process shows that, after link and peer BFD for VRRP is deployed, the backup device immediately preempts the Master state if a fault occurs. Link and peer BFD for VRRP implements a millisecond-level master/backup VRRP switchover.

Benefits

BFD for VRRP speeds up master/backup VRRP switchovers if faults occur.

Translation
Download
Updated: 2019-01-03

Document ID: EDOC1100055045

Views: 11564

Downloads: 34

Average rating:
This Document Applies to these Products
Related Version
Related Documents
Share
Previous Next