From: Carlos G Mendioroz (tron@huapi.ba.ar)
Date: Thu Oct 27 2005 - 12:37:40 GMT-3
Hmm,
HSRP works between DSWs, and they are connected through the ASW as long
as both links are up. Standard cisco design advices not to have DSWs
directly linked.
ASW
/ \
/ \
DSW1 DSW2
So when any of the ASW - DSW links breaks, HSRP is not happy.
But both are isolated islands, in the same IP subnet (unless the L#
interface goes down altogether in the DSW).
-Carlos
Brant I. Stevens @ 27/10/2005 12:23 dixit:
> In order for HSRP to work properly, routers in a given group would need
> Layer 2 adjacency. In the case of an ASW-DSW link failing, the "other" link
> connecting the access switch to the distribution would carry the traffic,
> and HSRP would be happy.
>
> Do you mean if the DSW-DSW link fails? In that scenario, HSRP would peer
> across the access layer (if the links were either (a)trunks that carried the
> management VLAN, or (b) in the same VLAN)
>
> But both uplinks would have to be trunks in order for the access switch to
> continue to have access to the separate management VLAN HSRP group and pass
> user traffic at the same time.
>
> -----Original Message-----
> From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
> Carlos G Mendioroz
> Sent: Thursday, October 27, 2005 11:07 AM
> To: ccielab@groupstudy.com
> Subject: OT: HSRP in multilayer switching architecture
>
> Hi,
> I'm back again with this topic, "HSRP backtraffic howto" so to say.
>
> While reading (again) the campus network design paper, I see that you can
> use HSRP to have default GW for ASWs (Access switches) to reach the world in
> case of DSW (Distribution switch) failure.
> So basically ASWs do have dedicated IP subnets (usually two for load
> balancing) and then is a DSW goes down, the remaining DSW (they go in
> pairs) takes the whole traffic.
>
> Great.
>
> But what happens if a ASW - DSW link goes down ?
> HSRP still works because DSWs are linked by the failing link, so both
> pretend to be active (isolated I guess) and the one talking to the ASW does
> the job. But what about the traffic going to the ASW ? Both DSW are layer 3
> active on that IP subnet, and unless there is hardware indication of the
> link down at the switch, traffic will be half dropped.
>
> Am I missing something ?
>
> Regards,
> --
> Carlos G Mendioroz <tron@huapi.ba.ar> LW7 EQI Argentina
>
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-- Carlos G Mendioroz <tron@huapi.ba.ar> LW7 EQI Argentina
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