glbp query

marcusaureliusbrutus

Hi,

Just wish to clarify some glbp concepts. Is the glbp weight referring to the bandwidth of the interface or the number of hosts? Cisco doc says that if the capacity of routerA is twice that of routerB then the weight should be assigned 160 and 80 respectively. But how do you know what initial weight value to assign? Can i use 80 and 40 as well since it presents the same ratio?

Thanks in advance.

marcusaureliusbrutus

Just a quick addition,

glbp 1 weighting 100 lower 91 upper 99
glbp 1 weighting 160


Does the above mean that 160 mac addresses is equivalent to 100%?
That if the current weight drops below 91% of 160, then the router
will no longer forward traffic?

Thanks again.

SysAdmin4066

Its an arbitrary number, weight is something you set. So I think you've got the gist, the numbers are unimportant, so long as they represent the ratio you are looking for and accomplish the forwarding you're looking to achieve.

marcusaureliusbrutus

Thanks SysAdmin4066. However could you further clarify the below?

given:

glbp 1 weighting 100 lower 91 upper 99


Does the above config indicate that the weight would initially be 100?
If i only have one host currently forwarded by the AVF, would that affect the current weight? If not, what would cause the weight to drop without tracking?

Thanks again.

yuriz43

weighting is the initial value. Upper value specifies the weight you must rise above to become an AVF. This is useful in situations where you're tracking multiple interfaces and would like to prevent your router from becoming an AVF when only 1 out of 3 interfaces come back online.

Take the following example:

Fa0/1 - Tracked, -25
Fa0/2 - Tracked -25
Fa0/3 - Tracked, -25


GLBP:

weighting 150 lower 76 upper 149


All three interfaces go offline. This brings you to 75. Below 76 which means you drop from AVF state.


2 interfaces come back online, however you do not become AVF because you do not meet the upper requirement.

last interface comes back online and now you can become AVF again.

SysAdmin4066

Yuriz has got you covered.

ZblaJhaNi

Hi,

Just a quick question about GLBP.
I understand the AVG election (higher priority or higher ip address), i understand the interface tracking and corresponding weighting.

But something is still not clear to me.

example:

-6 routers is GLBP group
-AVG elected because of priority 200
-all other routers: default priority, default weight, no tracking.....

On which criteria are than the AVF`s elected?
Is the first criteria weighting (and if it is), and than the higher IP address?!

Thanks for help

BR

jeanathan

ZblaJhaNi wrote: »

Hi,

Just a quick question about GLBP.
I understand the AVG election (higher priority or higher ip address), i understand the interface tracking and corresponding weighting.

But something is still not clear to me.

example:

-6 routers is GLBP group
-AVG elected because of priority 200
-all other routers: default priority, default weight, no tracking.....

On which criteria are than the AVF`s elected?
Is the first criteria weighting (and if it is), and than the higher IP address?!

Thanks for help

BR

From my understanding there is one AVG that handles virtual mac address assignments to host. All active routers in the group with a priority value (weighting) higher than the lower threshold value will be virtual forwarding routers (AVF) on behalf of host. The AVG will assign the virtual mac addresses in a round robin fashion to host so that they are load balanced across all active forwarding routers (AVF's). The minimum threshold value is the cutoff point for whether or not the router is an AVF, it still can be the AVG but is no longer an AVG+AVF, and so if your priority value - the interface tracking decrement value is lower than the lower threshold value you will no longer forward traffic in the GLBP group. I don't remember what the upper threshold value is for.

You might want to get a second opinion on this I too am just learning it.

DevilWAH

ZblaJhaNi wrote: »

On which criteria are than the AVF`s elected?
Is the first criteria weighting (and if it is), and than the higher IP address?!

Thanks for help

BR

If all other things are eaqual it is much like msot other thing in cisco, it becomes things like mac addess / ip address on the GLBP interface.

usualy it is the lower port mac address that if every thing else is eaqual will be used.

ZblaJhaNi

jeanathan wrote: »

.The minimum threshold value is the cutoff point for whether or not the router is an AVF, it still can be the AVG but is no longer an AVG+AVF, and so if your priority value - the interface tracking decrement value is lower than the lower threshold value you will no longer forward traffic in the GLBP group. I don't remember what the upper threshold value is for.

HI,

From my point of understanding; if the minimum threshold is reached the router is not an legitimate AVF anymore and it must reached upper threshold again to become a AVF candidate.

If the weight falls from the maximum weight in between the upper and lower threshold, the router is still a AVF candidate.

My two cents