GLBP
One issue with both HSRP and VRRP is that only the primary router is in use; the others must wait for the primary to fail before they are used.
These two protocols use groups to get around that limitation. However, Gateway Load Balancing Protocol (GLBP) enables the simultaneous use of up to four gateways, thus maximizing bandwidth.
With GLBP, there is still one virtual IP address. However, each participating router has a virtual MAC address, and different routers’ virtual MAC addresses are sent in answer to ARPs for the virtual IP address.
GLBP can also use groups up to a maximum of 1024 per physical interface. GLBP is supported only on Cisco 4500 and 6500 series switches.
The load sharing is done in one of three ways:
The actual router used by a host is its Active Virtual Forwarder (AVF). GLBP group members multicast hellos every 3 seconds to IP address 224.0.0.102, UDP port 3222.
If one router goes down, another router answers for its MAC address.
Configure GLBP with the interface command :
glbp group-number ip virtual-IP-address, as shown:
Router(config-if)# glbp 39 ip 10.0.0.1
To ensure deterministic elections, each router can be configured with a priority. The default priority is 100:
Router(config-if)# glbp 39 priority 150
Hello and hold (or dead) timers can be configured for each interface with the command glbp group-numbertimers [msec] hello-time[msec] hold-time.
Values are in seconds unless the mseckeyword is used.
GLBP can also track interfaces just as with HSRP. If a tracked interface goes down, another router answers for the first router’s MAC address.
One issue with both HSRP and VRRP is that only the primary router is in use; the others must wait for the primary to fail before they are used.
These two protocols use groups to get around that limitation. However, Gateway Load Balancing Protocol (GLBP) enables the simultaneous use of up to four gateways, thus maximizing bandwidth.
With GLBP, there is still one virtual IP address. However, each participating router has a virtual MAC address, and different routers’ virtual MAC addresses are sent in answer to ARPs for the virtual IP address.
GLBP can also use groups up to a maximum of 1024 per physical interface. GLBP is supported only on Cisco 4500 and 6500 series switches.
The load sharing is done in one of three ways:
- Weighted load balancing:Traffic is balanced proportional to a configured weight.
- Host-dependent load balancing:A given host always uses the same router.
- Round-robin load balancing:Each router MAC is used to respond to ARP requests in turn.
- GLBP routers elect an Active Virtual Gateway (AVG). It is the only router to respond to ARPs. It uses this capacity to balance the load among the GLBP routers. The highest priority router is the AVG; the highest configured IP address is used in case of a tie.
The actual router used by a host is its Active Virtual Forwarder (AVF). GLBP group members multicast hellos every 3 seconds to IP address 224.0.0.102, UDP port 3222.
If one router goes down, another router answers for its MAC address.
Configure GLBP with the interface command :
glbp group-number ip virtual-IP-address, as shown:
Router(config-if)# glbp 39 ip 10.0.0.1
To ensure deterministic elections, each router can be configured with a priority. The default priority is 100:
Router(config-if)# glbp 39 priority 150
Hello and hold (or dead) timers can be configured for each interface with the command glbp group-numbertimers [msec] hello-time[msec] hold-time.
Values are in seconds unless the mseckeyword is used.
GLBP can also track interfaces just as with HSRP. If a tracked interface goes down, another router answers for the first router’s MAC address.
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