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HSRP Question.

Posted on 2008-06-26
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Last Modified: 2008-06-26
I have two Catalyst6509 connected through trunk.

 Have fastEthernets of both 6509 into a VLAN. Connected these fastEthernets to a Layer-2 switch and associated the interfaces in the L-2 switch to the same VLAN. Configured HSRP on the 6509 Vlans.

That means HSRP messages have two paths to between each Cat6509.
1. Through the trunk
2. Through the L2 switch.

 My question here is, which path will the HSRP hello message take?

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Question by:ravisimpi
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by:Don Johnston
Don Johnston earned 800 total points
ID: 21873754
> My question here is, which path will the HSRP hello message take?

Whichever one spanning tree is NOT blocking. :-)

While you may have two physical paths, both of them can't be forwarding traffic (or at least they shouldn't be). If you do a "show span" on all three switches, you'll see that on one of them, your VLAN is being blocked on one of the switch-to-switch links.
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harbor235 earned 1200 total points
ID: 21874238
HSRP is between the 6509s, I suspect one of them is the root bridge? Preferrably the root bridge is
defined to be on the 6509 nearest to the preferred layer 3 egress point.

The hsrp hello message is will go over the directly connected trunk between the 6509s if one of them is root for the vlan in question. If you did not nail down the root to one of the 6509s and the L2 switch is root then it will go through the layer 2 switch since all paths to that vlan directly connected to the root must be active.

harbor235 ;}

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by:ravisimpi
ID: 21874558
The problem here is that the L2 switch (which actually is a ATCA shelf having different modules which act as a L2 switch) don't support STP. Now I want to force the HSRP messages to go through this L2 switch first, and not through trunk or probably secondary path should be the trunk.



 
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by:harbor235
ID: 21874850

If one of the 6509's is root then this is not possible, and since the other device does not speak STP it is not possible in your configuration.

Having a device act as a switch that does not support STP in your switch mesh is dangerous, I also cannot imagine why you would want  to run hsrp between the 6509s and not want the failover mechinisms inherent with HSRP to comminucate over a directly connected link.  Anything else increases the failure domain of the configuration.

harbor235 ;}
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