HSRP, preempt, spanning tree root and portfast.

[bruce.porter]

I have some dual homed servers connected to 6513s. The servers are connected to the same vlan on each router.

Documentation seems a bit weak about HSRP configuration. From what I have gathered, you must set the vlan to preempt on both routers if you want to return to the primary router after the primary router's vlan returns to operation.

Does this also mean that should an individual link, attached to one of my servers, within that vlan fail and then return to operation, that that link would failover to the standby and then preempt back to the priority router?

How do you show this with either show commands or debug commands. I haven't been able to see this type of link-down-up by any debugging or show commands etc.

Next question: It would seem that the router with the higher priority Standby setting would cause that link to be the link used by my dual homed servers, iregardless of the spanning tree root priorities of either router for that vlan.

I would also think that, with portfast set, that spanning tree would be disabled and all associated timing delays associated with it avoided as well. So why specify a spanning tree root on one or the other routers? Just run portfast and use the standby priority to determine which link on the server will be primary.

Thx

[right_guy12]

Hi! Bruce,

As far as I am aware you are correct in thinking that you have to set your vlan to pre-empt on one or both routers, so that the primary router can become active when it returns to normal operation.

In case an individual link attached to your server fails, I believe that it would'nt cause a change in active vlan on the router, what it would do is route the traffic through standby router.

Hope it helps...

Regards.

[right_guy12]

Hi! Bruce,

You can use the command "show standby" to view detailed information and "show standby brief" to view information on active vlans in brief.

Hope it helps...

Regards.

[ankurbhasin]

HI Bruce,

You need not configure preempt on both the routers if you have HSRP running for single vlan in a single group.

You can just configure preempt on the router which you think should always be active router and incase it goes down due to some reason and comes up again later should become active again.

Yes if your individual link attached to your server within that vlan fail the standby link will take over the connection but incase your primary link comes up the preempt feature comnfigured on active router will make that link active again.

To check the status of the router which is active and which is in standby state just run the command "sh standby" on any of the router and it will show you which router is active and which router is standby.

So as you asked about the show command you can run

"show standby" to check the HSRP routres status

To know more about HSRP you can read this document

http://www.cisco.com/univercd/cc/td/doc/product/lan/c3550/12120ea2/3550scg/swhsrp.htm#wp1044503

Coming to your last question now

If you configure spanning tree root command that will decide which should be the root bridge for that vlan but in your topology there is no loop between the 2 swicth router and your dual nic cards.

Also your NIC cards will not understand the STP BPDU so STP root command will definetely make the root bridge but will not hamper your traffic decision.

Also setting the spanning tree portfast will never disables the STP it will just reduce the convergence time so incase your ports on which nic is connected goes down will just take few seconds to come up because of STP portfast configured.

Because you have nic cards directly connected to the switch routers STP will not play a major role here.

HTH, if yes please rate the post.

Ankur