GLBP

GLBP (Gateway Load-Balance Protocol) - 

Allow FHRP and load-balance traffic for the local segment.

For each segment there is 1 AVG (Active Virtual Gateway) which responsible for determine who will be the AVF (Active Virtual Forwarder) and up to 4 AVF’s.

Here is the following lab I setup in GNS:

R1, R2 and R3 are configured as GLBP group 1 for R4 and R6, R4 and R6 configured with default route to 10.1.0.254.

R1 Configuration:

interface FastEthernet1/0  ip address 10.1.0.1 255.255.255.0  glbp 1 ip 10.1.0.254  glbp 1 priority 110  glbp 1 preempt  glbp 1 authentication md5 key-string cisco  duplex full  speed 100 end

R2 Configuration:

interface FastEthernet1/0  ip address 10.1.0.2 255.255.255.0  glbp 1 ip 10.1.0.254  glbp 1 priority 120  glbp 1 preempt  glbp 1 authentication md5 key-string cisco  duplex full  speed 100 end

R3 Configuration:

interface FastEthernet1/0  ip address 10.1.0.3 255.255.255.0  glbp 1 ip 10.1.0.254  glbp 1 priority 130  glbp 1 preempt  glbp 1 authentication md5 key-string cisco  glbp 1 load-balancing host-dependent  duplex full  speed 100 end

A little explanation on the above configuration:

glbp 1 ip is very similar to HSRP or VRRP virtual IP, it’s he layer 3 IP which hosts refer to.

glbp 1 priority decide which router will be the AVG, higher priority wins.

glbp 1 preempt and authentication – again similar to HSRP/VRRP, no need to explain

glbp 1 load-balancing determine the way the AVG will load the traffic between the AVF’s, there are 3 modes for this option:

Host-depended – the source of the MAC address determine the AVF, which provides persistency. This method is recommended for segment with no more then 20 hosts.

Round-robin – the default option, in equal cyclic manner load-balance between the AVF’s

Weighted - Load balance in proportion to forwarder weighting. The default weight for each AVF is 100 and can be configured with glbp 1 weighting and can be monitored by track objects.