GLBP: Gateway Load balancing Protocol Basics
Today i will talk about the load balancing protocol and is named as "GLBP-Gateway Load balancing Protocol. Before starting with the concept of the GLBP make sure you are aware of the other two protocols named as HSRP- Hot standby routing protocol and VRRP-Virtual Router Redundancy Protocol.
Once you understand both the protocol, then go with this article to understand the GLBP protocol basics. I will come up with the configuration part of HSRP, VRRP and GLBP in another article and will also take care of the difference between all these protocol in details.
Lets start with the GLBP protocol basics now.
GLBP actually provides load balancing over multiple routers and that can be multiple gateways using a single virtual IP address and multiple virtual MAC addresses. Each host is configured with the same virtual IP address, and all routers in the virtual router group participate in forwarding packets.
Basics about GLBP-Gateway Load balancing Protocol
Members of a GLBP group elect one gateway from all the routers and to be the active virtual gateway (AVG) for that group. Other routers in the group will provide backup for the AVG in the process and if AVG becomes unavailable, one of the router from the group will be AVG. The AVG assigns a virtual MAC address to each member of the GLBP group. Each gateway assumes responsibility for forwarding packets sent to the virtual MAC address assigned to it by the AVG. These gateways are known as active virtual forwarders (AVFs) for their virtual MAC address.
Once you understand both the protocol, then go with this article to understand the GLBP protocol basics. I will come up with the configuration part of HSRP, VRRP and GLBP in another article and will also take care of the difference between all these protocol in details.
Lets start with the GLBP protocol basics now.
GLBP actually provides load balancing over multiple routers and that can be multiple gateways using a single virtual IP address and multiple virtual MAC addresses. Each host is configured with the same virtual IP address, and all routers in the virtual router group participate in forwarding packets.
Basics about GLBP-Gateway Load balancing Protocol
- GLBP is a cisco Propriety Protocol
- GLBP is a load balancing protocol while HSRP and VRRP are not.
- GLBP supports for IPv6 addressing Scheme as well.
- Hello messages sent every 3 seconds to the multicast address 224.0.0.102
- It uses User Datagram Protocol (UDP) port 3222 (source and destination).
- Similar to HSRP and VRRP, GLBP default priority is 100.
- GLBP supports up to 1024 virtual routers (GLBP groups) on each physical interface of a router, and up to 4 virtual forwarders per group.
- Default convergence time is 10 seconds.
- Redundancy scheme of GLBP enables you to preempt an active virtual gateway with a higher priority backup virtual gateway that has become available.
- In GLBP, the redirect timer interval in the range from 0 to 3600 seconds. The default is 600 seconds
- The timeout time interval, in the range from 600 to 64,800 seconds, before the secondary virtual forwarder becomes unavailable.The default is 14,400 seconds (4 hours).
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| Fig 1.1- GLBP Operation |
If we are talking about the GLBP operation,it actually operates virtual gateway redundancy in the same way as HSRP. One gateway is elected as the AVG, another gateway is elected as the standby virtual gateway, and the remaining gateways are placed in a listen state.
If in case AVG fails, the standby virtual gateway will takeover the responsibility for the virtual IP address. A new standby virtual gateway is then elected from the gateways in the listen state.
VFR-Virtual forwarder redundancy is similar to virtual gateway redundancy with an AVF. If the AVF fails, one of the secondary virtual forwarders in the listen state assumes responsibility for the virtual MAC address.
The new elected AVF is also a primary virtual forwarder for a different forwarder number. GLBP then migrates hosts away from the old forwarder number using two timers that start as soon as the gateway changes to the active virtual forwarder state. GLBP uses the hello messages to communicate the current state of the timers.
The redirect time is the interval during which the AVG continues to redirect hosts to the old virtual forwarder MAC address. When the redirect time expires, the AVG stops redirecting hosts to the virtual forwarder, although the virtual forwarder will continue to forward packets that were sent to the old virtual forwarder MAC address.
The secondary hold-time is the interval during which the virtual forwarder is valid. When the secondary holdtime expires, the virtual forwarder is removed from all gateways in the GLBP group. The expired virtual forwarder number becomes eligible for reassignment by the AVG.
