This is a very common design in a campus backbone to track the vlan uplink from the distribution layer to the core layer. In that design, there is only one port at L2 that is in the uplink vlan (i.e. it is a point-to-point L3 vlan). So, when that one port goes down, auto-state brings the vlan down and HSRP can fail-over.
Chris ""Frank Merrill"" wrote in message [EMAIL PROTECTED]">news:[EMAIL PROTECTED]... > Comments in-line... > > Phil Lorenz wrote: > > > > I'm a little confused by configs I see in production that > > appear to be > > contrary to how I think HSRP works. > > > > What is the significance of the preempt statement on Switch #2 > > in this > > example below ??? > > In your example there isn't a preempt command on the second one, but I'm > assuming you mean if there is one there... > > I also assume you mean router? (Must be an RSM or MSFC since it has VLAN > interfaces!) > > > > > Is it- without the preempt statement on the second switch (even > > though > > it > > has the lower priority), the HSRP priority would not change > > back if > > Switch > > #1 flapped a few times ??? > > It would switch back if 'preempt' is configured on the first one. > We commonly configure all HSRP routers in an HSRP group with 'preempt' > because we might have 4 routers in the group. > > This way we can assure that the 'preferred' order (1,2,3,4 for example) will > be maintained in a multiple failure scenario. > Of course the last one in a group shouldn't need it, but, it's more > consistent to configure it, and it won't hurt a thing. > > Given such a scenario with four HSRP routers in a group: > If the first and second routers failed, then the third would become the > active one. If the second one came back, we want it to be the active one (if > number 1 is still down), and if we didn't configure 'preempt' on it, number > 3 would be the gateway for that group until number 1 came back up. > That could possibly be a less than desirable router-load situation on the > VLAN/network that these four routers are on. > > > > > ex: > > Switch #1 > > > > inter vlan 1 > > 10.10.10.1 255.255.255.0 > > standbye priority 255 preempt > > standbye IP 10.10.10.3 > > standby track vlan 101 > > > > Switch #2 > > > > inter vlan 1 > > 10.10.10.2 255.255.255.0 > > standbye priority 254 > > standbye IP 10.10.10.3 > > standby track vlan 102 > > > > Thanks > > Phil > > > Hmmm... Vlan tracking? Although it technically will work, your VLAN > interfaces will only go down if you have no active switch ports in them. > > Good Luck! Message Posted at: http://www.groupstudy.com/form/read.php?f=7&i=44927&t=44762 -------------------------------------------------- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
