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| Hi guys,
Long story short: I brought up a router with HSRP statements that were misconfigured, and down 16 remote locations... in 3 seconds. Ouch. We are talking real live network, here, not a home lab. My mistake? The router was configured by someone else, who by the way is a whole lot more knowledgeable about Cisco than I am, and I did not check the config. Bottom line is 30mn of downtime.
So I scoured the internet for a simple explanation of HSRP, and found the most hilarious yet interesting article on HSRP. So I figured I would share!
http://routergod.com/paulhogan/
Hope this helps... | |
| jeff_j_black 2002-07-26, 8:55 am |
| Router God is sooo funny! What was your particular predicament? | |
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| The HSRP statements confused another router and populated the ARP cache with wrong info, which resulted in nobody being able to route anything anymore... | |
| jeff_j_black 2002-07-26, 9:07 am |
| So it related to the configured MAC addresses then? After reading the article I imagined that would be something that someone setting it up at another location could overlook or not be able to do. | |
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| basically, both routers were now seen as one sharing a "virtual" MAC address. That ended up creating the problem. HSRP is supposed to bring fault tolerance. One router goes down, the other takes over, and it is seamless to the user. But that means that both those routers must be equiped with the same routing table -- which they were not, hence the problems with routing... | |
| jeff_j_black 2002-07-26, 9:34 am |
| I see, thanks for the illustration. Have an awesome Friday. | |
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| you're welcome. I figured my mistake might as well benefit all of us  | |
| darthfeces 2002-07-26, 12:18 pm |
| i been working on a lot of projects lately
and i have the most problems when my boss half configs a router or firewall as opposed to me doing it from scratch.
look at it as good troubleshooting experience
for the lab. | |
| darthfeces 2002-07-26, 12:22 pm |
| i think i read somewhere that hsrp works best in an "internal" envionment,
we use it on our rsm's.
i guess on wan's good old fashioned physical
rendundacy is best. | |
| Yankee 2002-07-26, 3:16 pm |
| agreed, Darth....Our WAN is two pvcs, one to each HQs core (we have two major sites in North America) for us and HSRP is used only on the Campus LANs.
Works for us....smaller place may use two core routers for the WAN with a PVC to each. You don't pay much if anything for the extra PVC, primarily the cost is in the port speed.
Just a thought,
Yankee | |
| jeff_j_black 2002-07-26, 7:55 pm |
| Great thread, just gotta give it five stars. | |
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| Thanks Jeff. This was a real life issue that popped up that prompted me to research this stuff. I figured it might be of interest to this forum since we often end up lost in academia more than real world.
Thanks to the contributors of this thread as well. This is when we really learn together! | |
| darthfeces 2002-07-26, 8:23 pm |
| i think the reason is :
hsrp functions best when working with a
routing protocol such as ospf or eigrp that converges quickly. the reason for this is that hsrp relies heavily on multicast messaging and any
interruption of the transport of packets causes
instability and unpredictable behavior.
hsrp is designed to quickly re route packets
upon router or link failure without retranmissions
or drops.
hence , a lan enviornment would provide the optimum atmosphere
and a wan
well a wan is a wan. |
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