From: Chris Lewis \(chrlewis\) (chrlewis@cisco.com)
Date: Thu Sep 08 2005 - 10:28:56 GMT-3
The quotes to be taken from the command reference and it does seem to be
correct. It does not talk about router A re-establishing itself after it
fails, which is what the preempt command does. I guess the example in
the command reference is assuming the interfaces are brought up at the
same time and they negotiate the router with higher priority as the
active one. Regarding your second bullet, if Router A fails, Router B is
the only choice for taking over, regardless of priority or preempt.
The discussion of preempt in the configuration guide below may be of
additional help
http://www.cisco.com/univercd/cc/td/doc/product/software/ios122/122cgcr/
fipr_c/ipcprt1/1cfip.htm)
Chris
-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
Bob Nelson
Sent: Wednesday, September 07, 2005 9:19 PM
To: ccielab@groupstudy.com
Subject: HSRP and Track - 3550
Hello All:
I want to make sure I am clear on the preempt and track for HSRP.
Here is an example from the DocCD. My questions follow the example
In the following example, the tracking process is configured to track
the IP routing capability of serial interface 1/0. HSRP on Ethernet
interface 0/0 then registers with the tracking process to be informed of
any changes to the IP routing state of serial interface 1/0. If the IP
state on Serial interface 1/0 goes down, then the priority of the HSRP
group is reduced by 10.
If both serial interfaces are operational, then Router A will be the
HSRP active router because it has the higher priority.
However, if IP routing on serial interface 1/0 in Router A fails, then
the HSRP group priority will be reduced and Router B will take over as
the active router, thus maintaining a default virtual gateway service to
hosts on the 10.1.0.0 subnet.
Router A Configuration
track 100 interface serial1/0 ip routing !
interface Ethernet0/0
ip address 10.1.0.21 255.255.0.0
standby 1 ip 10.1.0.1
standby 1 priority 105
standby 1 track 100 decrement 10
Router B Configuration
track 100 interface serial1/0 ip routing !
interface Ethernet0/0
ip address 10.1.0.22 255.255.0.0
standby 1 ip 10.1.0.1
standby 1 priority 100
standby 1 track 100 decrement 10
1. "If both serial interfaces are operational, then Router A will be the
HSRP active router because it has the higher priority."
Is this necessarily true. Does it not depend on which interface
was brought up first?. Without preempt, A will not become active if it
is brought up second, correct?
Without the preempt command on Router A, it will not take over
just by virtue of the higher priority.
2. "if IP routing on serial interface 1/0 in Router A fails, then the
HSRP group priority will be reduced and Router B will take over as the
active router"
Again, just because the priority on A (assuming it is the active)
drops below router B's priority, does not mean it will take over as
active,
without B having preempt configured. Additionally, if B is
configured
to preempt A when Serial 1/0 goes down on router A, so it become the
active,
A must also have preempt configured to resume its active role when
the
serial comes up.
Is this correct and they just did not put the preempt statements for
brevity(confuse me) or am I missing the concept.
Thanks for the help. Sorry for the length, wanted to be complete
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