From: Hobbs (deadheadblues@gmail.com)
Date: Sat Sep 20 2008 - 15:47:32 ART
Thanks Darby. I do understand the need for the preemption delay, I will
check out that CCDA book. I was really wondering what the functional
differences were between "reloaded" and "restarted" if there were any...does
the router behave differently when its powered on/off or issued the reload
command?...and do the two options (minimum vs reload) refer to those
differences?
i hope that's a little clearer
On Sat, Sep 20, 2008 at 12:40 PM, Darby Weaver <ccie.weaver@gmail.com>wrote:
> This should answer the question:
>
> When a router first comes up, it does not have a complete routing table. If
> it is configured to preempt, it will become the active router, yet it is
> unable to provide adequate routing services. Solve this problem by
> configuring a delay before the preempting router actually preempts the
> currently active router.
>
> Remember routing protocols need time to reconverge. So the delay can be a
> handy feature in terms of increasing the stability of a given network.
> Otherwise we may see flapping and we may also lose traffic while the network
> stabilizes from the preemption.
>
> I found some more stuff below.
>
> Also if you have a chance to take a look at Diane Teare's CCDA Book from
> Cisco Press you will note she goes into ample detail explaining just how
> long this reconvergence can take and why under different failure scenarios.
>
> HTH
>
> Darby Weaver
>
> Later
>
>
>
>
>
> According to the Cisco Documentation for these commands they appear quite
> clear on the matter:
>
> 1. Defaults
>
> The default group number is 0.
> The default delay is 0 seconds; if the router wants to preempt, it will do
> so immediately.
> By default, the router that comes up later becomes the standby.
>
> 2. (Optional) Specifies the preemption delay, in seconds, after a reload
> only. This delay period applies only to the first interface-up event after
> the router has reloaded.
>
> Here's some verbage:
>
> When this command is configured, the router is configured to preempt, which
> means that when the local router has a Hot Standby priority higher than the
> current active router, the local router should attempt to assume control as
> the active router. If preemption* *is not configured, the local router
> assumes control as the active router only if it receives information
> indicating no router is in the active state (acting as the designated
> router).
>
> When a router first comes up, it does not have a complete routing table. If
> it is configured to preempt, it will become the active router, yet it is
> unable to provide adequate routing services. Solve this problem by
> configuring a delay before the preempting router actually preempts the
> currently active router.
>
> When group number 0 is used, no group number is written to NVRAM, providing
> backward compatibility.
>
> IP redundancy clients can prevent preemption from taking place. The *standby
> preempt* *delay* *sync* *seconds* command specifies a maximum number of
> seconds to allow IP redundancy clients to prevent preemption. When this
> expires, then preemption takes place regardless of the state of the IP
> redundancy clients.
>
> The* standby preempt* *delay* *reload* *seconds** *command allows
> preemption to occur only after a router reloads. This provides stabilization
> of the router at startup. After this initial delay at startup, the operation
> returns to the default behavior.
>
> The *no standby preempt delay* command will disable the preemption delay
> but preemption will remain enabled. The *no standby preempt delay minimum*
> *seconds* command will disable the minimum delay but leave any
> synchronization delay if it was configured. So this should answer the
> question:
>
>
>
>
> On Sat, Sep 20, 2008 at 1:20 PM, Hobbs <deadheadblues@gmail.com> wrote:
>
>> Hello,
>>
>> The HSRP preemption configuration options are as follows:
>>
>> standby [group-number] preempt [delay {minimum delay | reload delay | sync
>> delay}]
>>
>> I always thought that the "minimum" keyword was used for preemption when
>> the
>> router was already loaded and it's priority was just increased (through
>> tracking or other means). However the documentation explains it like this:
>>
>> *minimum *seconds
>> ...causes the local router to postpone taking over the active role for a
>> minimum number of seconds since that router was last restarted.
>>
>> *reload *seconds
>> Specifies the preemption delay, in seconds, after a reload only.
>>
>> What is the difference between reload and restarted in these explanations?
>>
>> thanks
>>
>>
>> Blogs and organic groups at http://www.ccie.net
>>
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