[nsp] HSRP

[Thomas Renzy]

Peter,

HSRP uses Multicast and the address is 224.0.0.2. HSRP also uses UDP on port
1985.

You can also HSRP to track interfaces and to change the priority in case
there is a problem with it. Here is an example of this.

interface Vlan10
 description Server-Vlan
 ip address 10.1.1.2 255.255.255.0
 standby ip 10.1.1.1
 standby priority 120 preempt
 standby track GigabitEthernet2/16 75

Here this vlan is tracking interface G2/16. The number "75" tells how much
the decrement the priority when the tracked interface goes down.

Thomas

Thomas Renzy 
IS&T Global Network Services
VERITAS Software
Office: +650-527-4734
Mobile: +650-248-1099
Fax: +650-527-2034

"Some people drink from the fountain of knowledge, others just gargle." -
Author Robert Anthony



-----Original Message-----
From: Peter B. Juul [mailto:peter.juul at uni-c.dk]
Sent: Thursday, June 19, 2003 12:17 PM
To: mac
Cc: cisco-nsp at puck.nether.net
Subject: Re: [nsp] HSRP


On Thu, Jun 19, 2003 at 08:29:37PM +0200, mac wrote:

> can one give me a quick explanation of HSRP is and how works?

Sure. HSRP, Hot Standby Router Protocol.

The concept is that you have two routers connected to the same Layer 2
network, say 10.1.0.2/24 and 10.1.0.3/24.

You configure the hosts on the net to use 10.1.0.1 as their default
gateway and you then configure HSRP with a virtual IP address of 10.1.0.1.

The routers then decide amongst each other which of them is to be 10.1.0.1
now and the hosts use that router.

Should that router die a horrible death (or should you decide to shutdown
the interface, yank the wire or somesuch) the other router notices and 
quickly takes over the IP address and (as far as I remember) the MAC address
so the ARP tables doesn't make a fuss. 

You can set up priorities for the routers and you can ask them to pre-empt,
so that when the first router is back on line, it takes over again.

It works a charm to my experience.

(It is, afaik, the Cisco version of that which became VRRP. However, VRRP
uses unicast for checking the status whereas HSRP uses multicast. Please,
someone correct me if that's pure nonsense.)

Peter B. Juul, 
Uni·C (PBJ255-RIPE)
_______________________________________________
cisco-nsp mailing list  cisco-nsp at puck.nether.net
http://puck.nether.net/mailman/listinfo/cisco-nsp
archive at http://puck.nether.net/pipermail/cisco-nsp/