From: Kenneth Wygand (KWygand@customonline.com)
Date: Tue Oct 07 2003 - 00:37:11 GMT-3
Sam,
OK, I just did a lot more testing to answer your question accurately.
No, the hello with the lowered priority is not necessarily sent out immediately - the hello with the CHANGED priority is sent out immediately, but it can also be a raised priority. Now, this does not necessarily dictate that the router with the highest priority will immediately assume the role of the active router. Remember from my last email that the "active" state of a router only changes when the router with the HIGHEST priority receives a hello packet from the other router(s) with a LOWER priority.
Lets look at it this way. Say you have routers R1 and R2. Let's say we sent the priority on R1 to be 105 and we leave R2 at the standard of 100. We'll "track" only the serial0 interface on R1 and we'll leave the standard decrement value of 10 (so when the serial0 interface is down, the priority of R1 will be 95).
Now R1 is the active router and R2 is on standby. They continue to exchange hello packets at regular intervals (every 3 seconds by default). Now interface serial 0 on R1 goes down. Immediately R1 decrements its priority value to 95 and sends out a hello packet to R2 stating that its priority is 95. R2 now realizes that the only other router on its segment that is part of the HSRP group is of lower priority than itself. It then sends a "COUP" message to R1 and promotes itself to "active" status and R1 will take over at standby.
Now lets continue the situation. So now R1 has interface serial 0 down and is priority 95 while R2 is priority 100. Now lets bring serial 0 back up on R1. Immediately the priority of router R1 becomes 105. This priority CHANGE causes a hello packet to be sent. So R1 sends R2 a hello packet informing R2 that R1's priority is now 105. R2, however, is currently the active router at priority 100. R2 WILL NOT DO ANYTHING IMMEDIATELY! R2 waits until it's hello timeout expires to inform R1 of its current priority of 100. Once this timeout expires, the hello packet is sent to R1 with the priority of 100. This is the trigger that starts R1 on its promotion to active status.
Hope this clears things up for you. If you have any other questions, don't hesitate to ask!
Ken
-----Original Message-----
From: sam_pilot@hotmail.com [mailto:sam_pilot@hotmail.com]
Sent: Mon 10/6/2003 8:41 PM
To: Kenneth Wygand
Cc:
Subject: Re: HSRP question
So the hello with the lowered priority is sent out immediately..
It does not wait for the next hello packet to be sent out.
Correct??.
Thanks for you help Kenneth
Regards
Sam
----- Original Message -----
From: "Kenneth Wygand" <KWygand@customonline.com>
To: <sam_pilot@hotmail.com>; <ccielab@groupstudy.com>
Sent: Monday, October 06, 2003 7:50 PM
Subject: RE: HSRP question
> Sam,
> As you correctly assumed, an HSRP router will not promote itself until it
receives a packet from it's neighbor with a LOWER priority than its own.
See the inline explanation I provided.
>
> 02:52:01: SB0:Ethernet0 Hello out 10.0.0.1 Active pri 105 hel 3 hol 10 ip
10.0.0
> .3
> 02:52:01: SB0:Ethernet0 Hello in 10.0.0.2 Standby pri 100 hel 3 hol 10 ip
10.0.0
> .3
> 02:52:04: SB0:Ethernet0 Hello in 10.0.0.2 Standby pri 100 hel 3 hol 10 ip
10.0.0
> .3
> 02:52:04: SB0:Ethernet0 Hello out 10.0.0.1 Active pri 105 hel 3 hol 10 ip
10.0.0
> .3
> 02:52:04: %LINEPROTO-5-UPDOWN: Line protocol on Interface Serial0, changed
state
> to down
> 02:52:04: SB0: Ethernet0 Now 0/1 tracked interfaces up
> 02:52:04: SB0: Ethernet0 Priority was 105 now 95, configured as 105
> ***************************************************
> **********ADVERTISEMENT AS LOWER PRIORITY**********
> ***************************************************
> 02:52:04: SB0:Ethernet0 Hello out 10.0.0.1 Active pri 95 hel 3 hol 10 ip
10.0.0.
> 3
> **********************************************************
> **********PROMOTION BY SIDE WITH HIGHER PRIORITY**********
> **********************************************************
> 02:52:04: SB0:Ethernet0 Coup in 10.0.0.2 Standby pri 100 hel 3 hol 10 ip
10.0.0.
> 3
>
> 02:52:04: %STANDBY-6-STATECHANGE: Standby: 0: Ethernet0 state
ve -> Spea
> k
> 02:52:04: SB0:Ethernet0 Resign out 10.0.0.1 Speak pri 95 hel 3 hol 10 ip
10.0.0.
> 3
> 02:52:04: SB0:Ethernet0 Hello out 10.0.0.1 Speak pri 95 hel 3 hol 10 ip
10.0.0.3
> 02:52:04: SB0:Ethernet0 Hello in 10.0.0.2 Active pri 100 hel 3 hol 10 ip
10.0.0.
> 3
> 02:52:07: SB0:Ethernet0 Hello in 10.0.0.2 Active pri 100 hel 3 hol 10 ip
10.0.0.
> 3
> 02:52:07: SB0:Ethernet0 Hello out 10.0.0.1 Speak pri 95 hel 3 hol 10 ip
10.0.0.3
> 02:52:10: SB0:Ethernet0 Hello out 10.0.0.1 Speak pri 95 hel 3 hol 10 ip
10.0.0.3
> 02:52:10: SB0:Ethernet0 Hello in 10.0.0.2 Active pri 100 hel 3 hol 10 ip
10.0.0.
> 3
> 02:52:12: SB0:Ethernet0 Hello in 10.0.0.2 Active pri 100 hel 3 hol 10 ip
10.0.0.
> 3
> 02:52:12: SB0:Ethernet0 Hello out 10.0.0.1 Speak pri 95 hel 3 hol 10 ip
10.0.0.3
> 02:52:14: %STANDBY-6-STATECHANGE: Standby: 0: Ethernet0 state
-> Stan
> dby
> 02:52:14: SB0:Ethernet0 Hello out 10.0.0.1 Standby pri 95 hel 3 hol 10 ip
10.0.0
> .3
> 02:52:15: SB0:Ethernet0 Hello in 10.0.0.2 Active pri 100 hel 3 hol 10 ip
10.0.0.
> 3
> =====================================================
> =====================================================
>
> 02:52:24: SB0:Ethernet0 Hello in 10.0.0.2 Active pri 100 hel 3 hol 10 ip
10.0.0.
> 3
> 02:52:24: %LINEPROTO-5-UPDOWN: Line protocol on Interface Serial0, changed
state
> to up
> 02:52:24: SB0: Ethernet0 Now 1/1 tracked interfaces up
> 02:52:24: SB0: Ethernet0 Priority was 95 now 105, configured as 105
> *******************************************
> EVEN THOUGH THIS ROUTER KNOWS IT IS HIGHER
> THAN THE OTHER SIDE, IT WAITS TO CONFIRM THAT THE
> OTHER SIDE IS INDEED OF LOWER PRIORITY BEFORE
> REQUESTING THE PROMOTION TO ACTIVE
> *******************************************
> 02:52:24: SB0:Ethernet0 Hello out 10.0.0.1 Standby pri 105 hel 3 hol 10 ip
10.0.
> 0.3
> 02:52:27: SB0:Ethernet0 Hello out 10.0.0.1 Standby pri 105 hel 3 hol 10 ip
10.0.
> 0.3
> ***************************************************
> **********ADVERTISEMENT AS LOWER PRIORITY**********
> ***************************************************
> 02:52:27: SB0:Ethernet0 Hello in 10.0.0.2 Active pri 100 hel 3 hol 10 ip
10.0.0.
> 3
> **********************************************************
> **********PROMOTION BY SIDE WITH HIGHER PRIORITY**********
> **********************************************************
> 02:52:27: SB0:Ethernet0 Coup out 10.0.0.1 Standby pri 105 hel 3 hol 10 ip
10.0.0
> .3
> 02:52:27: %STANDBY-6-STATECHANGE: Standby: 0: Ethernet0 state
ndby -> Acti
> ve
> 02:52:27: SB0:Ethernet0 Hello out 10.0.0.1 Active pri 105 hel 3 hol 10 ip
10.0.0
> .3
> 02:52:27: SB0: Ethernet0 changing MAC address to 0000.0c07.ac00
> 02:52:27: SB0:Ethernet0 Resign in 10.0.0.2 Speak pri 100 hel 3 hol 10 ip
10.0.0.
> 3
> 02:52:27: SB0:Ethernet0 Hello in 10.0.0.2 Speak pri 100 hel 3 hol 10 ip
10.0.0.3
> 02:52:29: SB0:Ethernet0 Hello out 10.0.0.1 Active pri 105 hel 3 hol 10 ip
10.0.0
> .3
> 02:52:29: SB0:Ethernet0 Hello in 10.0.0.2 Speak pri 100 hel 3 hol 10 ip
10.0.0.3
> 02:52:32: SB0:Ethernet0 Hello in 10.0.0.2 Speak pri 100 hel 3 hol 10 ip
10.0.0.3
> 02:52:32: SB0:Ethernet0 Hello out 10.0.0.1 Active pri 105 hel 3 hol 10 ip
10.0.0
> .3u all
> All possible debugging has been turned off
> R1#
> 02:52:35: SB0:Ethernet0 Hello in 10.0.0.2 Speak pri 100 hel 3 hol 10 ip
10.0.0.3
> 02:52:35: SB0:Ethernet0 Hello out 10.0.0.1 Active pri 105 hel 3 hol 10 ip
10.0.0
> .3
>
> HTH,
> Ken
>
> -----Original Message-----
> From: sam_pilot@hotmail.com [mailto:sam_pilot@hotmail.com]
> Sent: Mon 10/6/2003 5:58 PM
> To: ccielab@groupstudy.com
> Cc:
> Subject: HSRP question
>
>
>
> Can someone clarify how HSRP works when I am tracking a serial interface.
>
> Specifically if a tracked serial interface goes down, does HSRP wait for
the
> next hello packet with its lowered priority to go out (based on the hello
> timer)?
>
> Or does it do send out the hello packet immediately?
>
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This archive was generated by hypermail 2.1.4 : Mon Nov 24 2003 - 07:52:58 GMT-3