VRRP – Advanced Enterprise Campus Design

Virtual Router Redundancy Protocol (VRRP) is a router redundancy protocol defined in RFC 3768. VRRPv2 supports only IPv4. RFC 5798 defines VRRPv3 for both IPv4 and IPv6 networks. VRRP is based on Cisco’s HSRP but is not compatible with it. VRRP specifies an election protocol that dynamically assigns responsibility for a virtual router to one of the VRRP routers on a LAN. The VRRP router controlling the IP addresses associated with a virtual router is called the master, and it forwards packets sent to these IP addresses. The election process provides dynamic failover in the forwarding responsibility in the event that the master becomes unavailable. This allows any of the virtual router IP addresses on the LAN to be used as the default first-hop router by end hosts. The virtual router backup assumes the forwarding responsibility for the virtual router if the master fails. The default VRRP hello timer is 1 second, and the dead timer is 3 seconds. Unlike in HSRP, VRRP preemption is enabled by default. Similar to HSRP, to configure load balancing, different VRRP groups are configured for different VLANs. VRRP can also be configured to track the uplink to decrement the VRRP priority of the primary router.

Note

Use of the terms master and slave is ONLY in association with the official terminology used in industry specifications and standards and in no way diminishes Pearson’s commitment to promoting diversity, equity, and inclusion and challenging, countering, and/or combating bias and stereotyping in the global population of the learners we serve.

GLBP

Global Load Balancing Protocol (GLBP) is a Cisco-proprietary FHRP that allows packet load sharing among a group of routers. GLBP protects data traffic from a failed router or circuit, such as HSRP, while allowing packet load sharing between a group of redundant routers. Methods for load balancing with HSRP and VRRP work with small networks, but GLBP automatically allows for first-hop load balancing on larger networks.

Unlike HSRP, GLBP provides for load balancing between multiple redundant routers—up to four gateways in a GLBP group. It balances the load by using a single virtual IP address and multiple virtual MAC addresses. All the hosts are configured with the same virtual IP address, and all routers in the virtual router group participate in forwarding packets. By default, all routers in a group forward traffic and do load balancing automatically. GLBP members communicate between each other through hello messages sent every 3 seconds to the multicast address 224.0.0.102, User Datagram Protocol (UDP) port 3222.

Benefits of GLBP include the following:

• Load sharing: GLBP can be configured in such a way that traffic from LAN clients can be shared by multiple routers.
• Multiple virtual routers: GLBP supports up to 1024 virtual routers (GLBP groups) on each physical interface of a router.
• Preemption: GLBP enables you to preempt an active virtual gateway with a higher-priority backup.
• Authentication: Simple text password authentication is supported.