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A brief introduction to VRRP

Virtual routing redundancy protocol VRRP (Virtual Router Redundancy Protocol) communicates with the external network by combining several routing devices to form a virtual routing device and using the IP address of the virtual routing device as the user's default gateway. When the gateway equipment fails, the VRRP mechanism can select new gateway devices to undertake data traffic, so as to ensure the reliable communication of the network.

With the rapid popularity of the network and the deepening of related applications, a variety of value-added services (such as IPTV, video conferencing, etc.) have been widely deployed, the reliability of the basic network has increasingly become the focus of users, to ensure uninterrupted network transmission is very important for end users.

Typically, all hosts in the same network segment have the same default route with the gateway as the next hop. The messages sent by the host to other network segments will be sent to the gateway through the default route, and then forwarded by the gateway, so as to realize the communication between the host and the external network.

When the gateway fails, all hosts in this network segment with the gateway as the default route will not be able to communicate with the external network. Increasing the exit gateway is a common way to improve the reliability of the system. at this time, how to choose the route among multiple exits has become a problem that needs to be solved.

The emergence of VRRP solves this problem very well. Without changing the networking, VRRP can make multiple routing devices into a virtual router, and configure the IP address of the virtual router as the default gateway to realize the backup of the default gateway. When the gateway equipment fails, the VRRP mechanism can select new gateway devices to undertake data traffic, so as to ensure the reliable communication of the network.

In the local area network (such as Ethernet) with multicast or broadcast capability, VRRP can still provide a highly reliable default link when the gateway device fails, and the network outage problem after a single link failure can be effectively avoided without modifying the configuration information of the host and gateway devices.

II. VRRP principle

1. Overview of VRRP

Figure 1 schematic diagram of VRRP backup group

As shown in figure 1 above, HostA is dual-attributed to SwitchA and SwitchB through Switch. Configure the VRRP backup group on SwitchA and SwitchB, which is externally represented as a virtual router to achieve link redundancy backup.

We can deploy the VRRP protocol in the network shown in figure 1 above. The basic concepts of the VRRP protocol are introduced in combination with this figure:

1. VRRP router (VRRP Router):

A device running the VRRP protocol that may belong to one or more virtual routers, such as SwitchA and SwitchB.

2. Virtual router (Virtual Router):

Also known as VRRP backup group, which consists of a Master device and multiple Backup devices, is used as the default gateway for hosts in a shared local area network. For example, SwitchA and SwitchB together form a virtual router.

3. Master router (Virtual Router Master):

A VRRP device, such as a SwitchA, that is responsible for forwarding messages.

4. Backup router (Virtual Router Backup):

A group of VRRP devices that do not undertake forwarding tasks, and when Master devices fail, they will be elected to become new Master devices, such as SwitchB.

5 、 VRID:

The identity of the virtual router. For example, the VRID of a virtual router composed of SwitchA and SwitchB is 1.

6. Virtual IP address (Virtual IP Address):

The IP address of a virtual router. A virtual router can have one or more IP addresses configured by the user. For example, the virtual IP address of a virtual router composed of SwitchA and SwitchB is 10.1.1.10ip24.

7. IP address owner (IP Address Owner):

If a VRRP device uses the virtual router IP address as the real interface address, the device is called the IP address owner. If the IP address owner is available, it will usually become a Master.

For example, SwitchA, whose interface IP address is the same as the IP address of the virtual router, is 10.1.1.10 IP 24, so it is the owner of the IP address of this VRRP backup group.

8. Virtual MAC address (Virtual MAC Address):

The virtual router is based on the MAC address generated by the virtual router ID. A virtual router has a virtual MAC address in the format 00-00-5E-00-01-{VRID} (VRRP for IPv4); 00-00-5E-00-02-{VRID} (VRRP for IPv6).

When the virtual router responds to an ARP request, it uses the virtual MAC address instead of the real MAC address of the interface. For example, the VRID of a virtual router composed of SwitchA and SwitchB is 1, so the MAC address of this VRRP backup group is 00-00-5E-00-01-01.

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