glbp weighting

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Mar 17th, 2009
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glbp 1 weighting 110 lower 95 upper 105

glbp 1 weighting track 10 decrement 5


I understand that the weighting of my avf is 110, i also understand that when interface being tracked by id 10 goes down my weight is dropped by 5. So when I hit the upper 105 weight does forwarding stop, and if so what is purpose of lower weight. What happens if the weight goes below 95?

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Giuseppe Larosa Tue, 03/17/2009 - 08:59
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Hello Mike,

the command implements two thresholds:


when going under lower the router gives up the role of AVF (resigns)

the router regains the role of active AVF only when it is over the upper thresold


the highest the weigthing the better as HSRP priority


see


The weighting value of a virtual gateway is a measure of the forwarding capacity of the gateway. If a tracked interface on the router fails, the weighting value of the router may fall from the maximum value to below the lower threshold, causing the router to give up its role as a virtual forwarder. When the weighting value of the router rises above the upper threshold, the router can resume its active virtual forwarder role.


Use the glbp weighting track and track commands to configure parameters for an interface to be tracked. If an interface on a router goes down, the weighting for the router can be reduced by a specified value.


http://www.cisco.com/en/US/docs/ios/ipapp/command/reference/iap_d1.html#wp1039581



Hope to help

Giuseppe


mschooley Tue, 03/17/2009 - 09:06
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so in my sitation, I wouldn't give up avf role until 95 and wouldn't regain it until 105, so in reality since i'm only tracking one interface, them most I could ever decrement is 5, I would never give up avf role even when interface is down, I need to decrement by at least 15, then when interface comes back up will increment to 110 again and be avf again?

Giuseppe Larosa Tue, 03/17/2009 - 09:11
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Hello Mike,

yes you need to tune the thresholds and the decrement to achieve what you want:


if you want the router to gives up AVF role when wan interface is down use


110 normal weight, 95 lower 105 upper


use decrement 16 to go to 94 when down


The optional value argument specifies by how much to decrement the GLBP gateway weighting when a tracked interface goes down. When the tracked interface comes back up, the weighting is incremented by the same amount.


http://www.cisco.com/en/US/docs/ios/ipapp/command/reference/iap_d1.html#wp1039581



I've preferred to verify but the increment will be equal to the decrement


Hope to help

Giuseppe


Laurent Aubert Tue, 03/17/2009 - 09:07
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Hi,


GLBP weighting is useful if you have serveral WAN interfaces on the same router.


You track each of them separately and each time you loose one, you decrease your weight. If the value is still above the lower limit, you continue to forward traffic but you receive less traffic if the load-balancing is based on weight.


If you have been removed from the group, you need to reach the upper limit before becoming an AVF again so you should set the lower and upper limit to the same value which should be reached only when you lost all your tracked interface. This way, you become an AVF as soon as you have at least one tracked interface operational.



HTH


Laurent.

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