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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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Basic VRRP Concepts

Basic VRRP Concepts

As shown in Figure 5-5, two gateways are grouped to form a virtual gateway, and the user host uses the virtual gateway's IP address as the default gateway IP address to communicate with the external network. If the default gateway fails, VRRP elects a new gateway to provide access services for the user.
Figure 5-5 VRRP networking

Basic VRRP concepts are described as follows:
  • Virtual router: also called a VRRP backup group, consists of a master router and one or more backup routers. A virtual router is a default gateway used by hosts within a shared local area network (LAN). A virtual router ID and one or more virtual IP addresses together identify a virtual router.
    • Virtual router ID (VRID): ID of a virtual router. Routers with the same VRID form a virtual router.

    • Virtual IP address: IP address of a virtual router. A virtual router can have one or more virtual IP addresses, which are manually assigned.

    • Virtual MAC address: MAC address generated by a virtual router based on a VRID. A virtual router has one virtual MAC address, in the format of 00-00-5E-00-01-{VRID} (VRRP for IPv4) or 00-00-5E-00-02-{VRID} (VRRP for IPv6). After a virtual router receives an ARP (VRRP for IPv4) or NS (VRRP for IPv6) request, it responds to the request with the virtual MAC address rather than the actual MAC address.

  • IP address owner: VRRP router that uses the virtual IP address as its interface IP address. If an IP address owner is available, it functions as the master router.

  • Primary IP address: IP address selected from actual interface IP addresses, which is usually the first IP address that is configured. The primary IP address is used as the source IP address in a VRRP Advertisement packet.

  • VRRP router: device running VRRP. A VRRP router can join one or more VRRP backup groups. A VRRP backup group consists of the following VRRP routers:
    • Master router: forwards packets and responds to ARP requests.

    • Backup router: does not forward packets when the master router is working properly, but can be elected as the new master router if the master router fails.

  • Priority: priority of a router in a VRRP backup group. A VRRP backup group elects the master and backup routers based on router priorities.

  • VRRP working modes:
    • Preemption mode: A backup router with a higher priority than the master router preempts the Master state.

    • Non-preemption mode: When the master router is working properly, a backup router does not preempt the Master state even if it has a priority higher than the master router.

  • VRRP timers:
    • Adver_Interval timer: The master router sends a VRRP Advertisement packet each time the Adver_Interval timer expires. The default timer value is 1 second.
    • Master_Down timer: A backup router preempts the Master state after the Master_Down timer expires. The Master_Down timer value (in seconds) is calculated using the following equation:

      Master_Down timer value = (3 x Adver_Interval timer value) + Skew_Time


      Skew_Time = (256 - Backup router's priority)/256

Updated: 2019-01-02

Document ID: EDOC1100055473

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