From: Chris Lewis \(chrlewis\) (chrlewis@cisco.com)
Date: Thu Sep 08 2005 - 12:03:04 GMT-3
I'd like to clarify my previous post by examining the behavior of the
commands in the command reference;
I take the following configuration directly from the documentation and
post it in to two routers in this configuration. I have to admit that
upon closer reading of the documentation, I have to be extremely
generous in my interpretation of the wording for it to be viewed as
totally correct.
S3/0
|
R3 (E0/0)----------(E0/0) R1 (e1/0)
R3
!
track 100 interface serial3/0 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
R1
track 100 interface E1/0 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
If I do a show standby on R1 immediately after entering these configs I
show this
Router1#show standby
Ethernet0/0 - Group 1
State is Speak
Virtual IP address is 10.1.0.1
Active virtual MAC address is 0000.0c07.ac01
Local virtual MAC address is 0000.0c07.ac01 (default)
Hello time 3 sec, hold time 10 sec
Next hello sent in 2.240 secs
Preemption disabled
Active router is 10.1.0.21, priority 105 (expires in 8.300 sec)
Standby router is unknown
Priority 100 (default 100)
Track object 100 state Up decrement 10
IP redundancy name is "hsrp-Et0/0-1" (default)
Then after a while I see the following on R3
R3#
*Sep 8 14:27:49.191: %SYS-5-CONFIG_I: Configured from console by
console
*Sep 8 14:27:58.631: %HSRP-6-STATECHANGE: Ethernet0/0 Grp 1 state
Standby -> Active
If I check back on R1, I now see this
Router1#show standby
Ethernet0/0 - Group 1
State is Standby
1 state change, last state change 00:00:23
Virtual IP address is 10.1.0.1
Active virtual MAC address is 0000.0c07.ac01
Local virtual MAC address is 0000.0c07.ac01 (default)
Hello time 3 sec, hold time 10 sec
Next hello sent in 0.472 secs
Preemption disabled
Active router is 10.1.0.21, priority 105 (expires in 8.532 sec)
Standby router is local
Priority 100 (default 100)
Track object 100 state Up decrement 10
IP redundancy name is "hsrp-Et0/0-1" (default)
Which shows R1 moving from Speak to Standby, R3 is now the active
router. If I shut down S3/0 on R3, the priority is reduced to 95, but it
remains as the active router (but note the standby router has changed to
R1, which could be a trick wording in the exam), as shown by the output
of the debug standby terse and show standby command
R3(config)#int s3/0
R3(config-if)#shut
R3(config-if)#
*Sep 8 14:36:35.195: HSRP: Et0/0 Grp 1 Track 100 object changed, state
Up -> Down
*Sep 8 14:36:35.195: HSRP: Et0/0 Grp 1 Priority 105 -> 95
R3#
*Sep 8 14:36:37.027: %LINK-5-CHANGED: Interface Serial3/0, changed
state to administratively down
*Sep 8 14:36:38.067: %LINEPROTO-5-UPDOWN: Line protocol on Interface
Serial3/0, changed state to down
R3#sho stand
Ethernet0/0 - Group 1
State is Active
2 state changes, last state change 00:17:56
Virtual IP address is 10.1.0.1
Active virtual MAC address is 0000.0c07.ac01
Local virtual MAC address is 0000.0c07.ac01 (default)
Hello time 3 sec, hold time 10 sec
Next hello sent in 2.652 secs
Preemption disabled
Active router is local
Standby router is 10.1.0.22, priority 100 (expires in 8.480 sec)
Priority 95 (configured 105)
Track object 100 state Down decrement 10
IP redundancy name is "hsrp-Et0/0-1" (default)
However if I reload R3, to simulate a failure of R3 (which is the way I
generously interpreted the phrase "if IP routing on serial interface 1/0
in Router A fails") this happens:
Router1#
*Sep 8 14:47:28.631: HSRP: Et0/0 Grp 1 Resign in 10.1.0.21 Active pri
95 vIP 10.1.0.1
*Sep 8 14:47:28.631: HSRP: Et0/0 Grp 1 Standby: i/Resign rcvd
(95/10.1.0.21)
*Sep 8 14:47:28.631: HSRP: Et0/0 Grp 1 Active router is local, was
10.1.0.21
*Sep 8 14:47:28.631: HSRP: Et0/0 Grp 1 Standby router is unknown, was
local
*Sep 8 14:47:28.631: HSRP: Et0/0 Grp 1 Standby -> Active
*Sep 8 14:47:28.631: %HSRP-6-STATECHANGE: Ethernet0/0 Grp 1 state
Standby -> Active
I think I was too generous in my interpretation of what the
documentation says. If it is relying on a failure of the router, there
is no need to have the track serial command.
Chris
-----Original Message-----
From: Chris Lewis (chrlewis)
Sent: Thursday, September 08, 2005 8:29 AM
To: 'Bob Nelson'; ccielab@groupstudy.com
Subject: RE: HSRP and Track - 3550
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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