GLBP on Nexus 7000's

Answered Question
Jun 14th, 2012

    We have GLBP configured on two Nexus 7000's using "load-balancing host-dependant" as our method of balancing. My question is, is there a quick way to determine which router each host is using. These are in production so any debugging is frowned on.

Thanks

David

I have this problem too.
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Correct Answer by krun_shah about 1 year 10 months ago

Available command to verify GLBP operation is following



show glbp [group group-number]

Displays the GLBP status for all or one group.

show glbp capability

Displays the GLBP capability for all or one group.

show glbp interface interface-type slot/port

Displays the GLBP status for an interface.

show glbp interface interface-type slot/port [active] [disabled] [init] [listen] [standby]

Displays the GLBP status for a group or interface for virtual forwarders in the selected state.

show glbp interface interface-type slot/port [active] [disabled] [init] [listen] [standby] brief

Displays a brief summary of the GLBP status for a group or interface for virtual forwarders in the selected state.

But none of these will show you which host uses which AVF. In GLBP, Hosts still point to a default gateway IP address, but GLBP causes different hosts to send their traffic to one of up to four routers in a GLBP group. To do so, the GLBP Active Virtual Gateway (AVG) assigns each router in the group a unique virtual MAC address format 0007.B400.xxyy, where xx is the GLBP group number, and yy is a different number for each router (01, 02, 03, or 04). When a client ARPs for the (virtual) IP address of its default gateway, the GLBP AVG replies with one of the four possible virtual MACs. By replying to ARP requests with different virtual MACs, the hosts in that subnet will in effect balance the traffic across the routers, rather than send all traffic to the one active router. You can check ARP table of host and see the mac address of default gateway. But this is not an easy way.

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Average Rating: 5 (1 ratings)
Correct Answer
krun_shah Fri, 06/15/2012 - 06:35

Available command to verify GLBP operation is following



show glbp [group group-number]

Displays the GLBP status for all or one group.

show glbp capability

Displays the GLBP capability for all or one group.

show glbp interface interface-type slot/port

Displays the GLBP status for an interface.

show glbp interface interface-type slot/port [active] [disabled] [init] [listen] [standby]

Displays the GLBP status for a group or interface for virtual forwarders in the selected state.

show glbp interface interface-type slot/port [active] [disabled] [init] [listen] [standby] brief

Displays a brief summary of the GLBP status for a group or interface for virtual forwarders in the selected state.

But none of these will show you which host uses which AVF. In GLBP, Hosts still point to a default gateway IP address, but GLBP causes different hosts to send their traffic to one of up to four routers in a GLBP group. To do so, the GLBP Active Virtual Gateway (AVG) assigns each router in the group a unique virtual MAC address format 0007.B400.xxyy, where xx is the GLBP group number, and yy is a different number for each router (01, 02, 03, or 04). When a client ARPs for the (virtual) IP address of its default gateway, the GLBP AVG replies with one of the four possible virtual MACs. By replying to ARP requests with different virtual MACs, the hosts in that subnet will in effect balance the traffic across the routers, rather than send all traffic to the one active router. You can check ARP table of host and see the mac address of default gateway. But this is not an easy way.

dvanhaaren Fri, 06/15/2012 - 06:45

Thanks Krun...You've confirmed what I thought. There is no easy way.

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Posted June 14, 2012 at 9:24 AM
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