Re: GLBP Priority Change

Nice explanation Pavel. The distinction of AVG from AVF is definitely one
that I think trips up a lot of folks.

On Mon, Oct 31, 2011 at 5:01 AM, Pavel Bykov <slidersv_at_gmail.com> wrote:

> 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
> >
> >
> > Blogs and organic groups at http://www.ccie.net
> >
> > _______________________________________________________________________
> > Subscription information may be found at:
> > http://www.groupstudy.com/list/CCIELab.html
> >
> >
> >
> >
> >
> >
> >
> >
>
>
> --
> Pavel Bykov
>
>
> Blogs and organic groups at http://www.ccie.net
>
> _______________________________________________________________________
> Subscription information may be found at:
> http://www.groupstudy.com/list/CCIELab.html
>
>
>
>
>
>
>
>

-- 
Regards,
Joe Astorino
CCIE #24347
Blog: http://astorinonetworks.com
"He not busy being born is busy dying" - Dylan
Blogs and organic groups at http://www.ccie.net