Re: GLBP Priority Change

Right. This is a tricky one.
Priority of AVG cannot be reduced dynamically via built-in tools.
However, you can do so via EEM (but then again, you can do pretty much
anything via EEM).

Here is the reasoning behind that logic:
AVG only needs a connection to the LAN, where it can hear about other AVFs
and standby virtual gateways.
The forwarding is done by AVFs, so this is where manipulation makes the
most sense.

Even if the AVG only has LAN connection, and all WAN connections have
failed, it will assign MAC address of other AVFs to the incoming ARP
requests.
And if AVG looses the LAN connection, then AVG state is assumed via standby
device.

You need to realize that the primary function of AVG in this case is to
reply to ARP requests from individual hosts, which it can do via only one
LAN connection. And the actual forwarding is performed by AVF. AVFs are
controlled by weights, which can be tracked as you mentioned. Therefore
tracking AVFs is the main concern. There is no real reason to track
priority of AVG.

Can you think of a scenario, where this will be needed? That might help in
explanation.

Here is the example:
2 routers, with VLAN555 running on LAN, and AVFs track WAN interface
reachability.
R1s WAN interface has failed, and therefore it cannot forward traffic
itself. Tracking reduced its weight, so the AVF on the R2 take over that
responsibility, and forwards all packets destined to that AVFs MAC address.
So the role in R1 in this case is just to reply to all ARP requests with
either AVF1 MAC or AVF2 MAC, but both AVF MACs are handled by R2.

R1#sh glbp brief
Interface Grp Fwd Pri State Address Active router Standby
router
Vl555 1 - 150 Active 5.5.5.1 local 5.5.5.6
Vl555 1 1 - Listen 0007.b400.0101 5.5.5.6 -
Vl555 1 2 - Listen 0007.b400.0102 5.5.5.6 -
R2#show glbp brief
Interface Grp Fwd Pri State Address Active router Standby
router
Vl555 1 - 140 Standby 5.5.5.1 5.5.5.5 local
Vl555 1 1 - Active 0007.b400.0101 local -
Vl555 1 2 - Active 0007.b400.0102 local -

If R1 would loose its LAN connection as well, then R2 would take over AVG
function as well.

HTH
On Sun, Oct 30, 2011 at 1:23 PM, Sandaka Ranatunga <
sandakaranatunga_at_gmail.com> wrote:

> Hi all,
>
> Can some body explian me how to reduce the GLBP Priority dynamically by
> tracking and object?
> is it possible to do ?
>
> When we track and object using "GLBP weighting " command, it will only
> dynamically change the weight but not Priority
>
> Please help on this
>
>
> Thanx
>
> Regards,
> Sandaka
>
>
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