GLBP active and priority settings

[getaway51]

Hi,

1)For GLBP , it is active-active R1 and R2 where Traffic will be send to R1 & R2 round-robin via the glbp IP unlike VRRP, right?

2)Therefore does traffic only send to higher priority "active GLBP"?

3)Wht is the default GLBP priority?  Btw wht is the use of priority if traffic send to both GLBP?

4)Can GLBP use for 3 routers? Wht is the limit

interface FastEthernet0/0

 ip address 10.0.254.20 255.255.255.0

 glbp 1 ip 10.0.254.10

 glbp 1 priority 120

 glbp 1 preempt

Router-B:

interface FastEthernet0/0

 ip address 10.0.254.30 255.255.255.0

 glbp 1 priority 100

 glbp 1 ip 10.0.254.10

 glbp 1 preempt

As in the previous article, the higher priority tells it to be the "active GLBP" router. 

[Deepak Kumar]

HI,

1)For GLBP , it is active-active R1 and R2 where Traffic will be send to R1 & R2 round-robin via the glbp IP unlike VRRP, right?

Ans:   Members of a GLBP group elect one gateway to be the active virtual gateway (AVG) for that group. Other group members provide backup for the AVG in the event that the AVG becomes unavailable. 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.

The AVG is responsible for answering Address Resolution Protocol (ARP) requests for the virtual IP address. Load sharing is achieved by the AVG replying to the ARP requests with different virtual MAC addresses.

In Figure 1, Router A is the AVG for a GLBP group, and is responsible01. Router B is a member of the same GLBP group and is designated as the AVF for the virtual MAC address 0007.b400.0102. Client 1 has a default gateway IP address of 10.21.8.10 and a gateway MAC address of 0007.b400.0101. Client 2 shares the same default gateway IP address  for the virtual IP address 10.21.8.10. Router A is also an AVF for the virtual MAC address 0007.b400.01but receives the gateway MAC address 0007.b400.0102 because Router B is sharing the traffic load with Router A.

2)Therefore does traffic only send to higher priority "active GLBP"?

Ans: No, AVG will responsible to manage the load balancing. 

3)Wht is the default GLBP priority?  Btw wht is the use of priority if traffic send to both GLBP?

Ans: The default priority is 100. Priority also determines if a GLBP router functions as a backup virtual gateway and the order of ascendancy to becoming an AVG if the current AVG fails. You can configure the priority of each backup virtual gateway with a value of 1 through 255 using the glbp priority command.

4)Can GLBP use for 3 routers? Wht is the limit

Ans:GLBP supports up to 1024 virtual routers (GLBP groups) on each physical interface of a router, and up to 4 virtual forwarders per group.

You can visit at https://www.cisco.com/en/US/docs/ios/12_2t/12_2t15/feature/guide/ft_glbp.html#wp1040147