What is a split horizon and route poisoning?

Question

Can someone tell me in simple terms, what is a split horizon and route poisoning? Please really use simple terms as I am no IT expert.

I was attending a talk on IT the other day and after the talk, I can go nuts!

Thank you guys for all your answers so far.

Answer 1

The poor guy said in Simple Terms!! look at all that IT cisco jargon there! lol

its basically very simple. Imagine this..
*A networking device (such as a switch or router) is connected in a way that allows information sent from it to loop back to it. For ex. It is connected to another device using 2 cables.
*It would damage your network functionality if the same date passes out from one of the connections and back in from the other connection causing a loop. PPL will get pissed coz the network is slow or unavailable. The net admin gets under a lot of pressure and eventually gets sacked.
** Here comes your terms to save the day.

When a device sends out some data.. it tags it with an ID.
If that data comes back to it (checking the ID) it will discard it and not send it back out (thus not allowing a loop to happen)

Thats it.. its pretty much Cisco propriatary stuff i guess..

Gluk ;)

Answer 2

1

Answer 3

Route Poisoning

Answer 4

These are Cisco terms, of which I am currently learning. Split horizon and route poisoning are basically the same. They prevent the router(s) from going into loops essentially with an information packet. The textbook definition of it is: reduces incorrect routing information and routing overhead in a distance-vector network by enforcing the rule that routing information cannot be sent back in the direction from which it was received. I think the second part of that definition will help you understand it better.

Answer 5

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RE:
What is a split horizon and route poisoning?
Can someone tell me in simple terms, what is a split horizon and route poisoning? Please really use simple terms as I am no IT expert.

I was attending a talk on IT the other day and after the talk, I can go nuts!

Answer 6

split horizon:
A routing technique that eliminates the chance of a routing scheme creating routing loops, effectively making routing more efficient. When a router in a network with only one data path receives a data packet, it does not send routing information back along the path on which the packet traveled (i.e., to an adjacent router); it only sends the information forward so that there is no possibility of the packet being routed back along the path it originally traveled.

route poisoning
Route poisoning is a way to prevent routing loops. Distance-vector routing protocols in computer networks use route poisoning to indicate to other routers that a route is no longer reachable and should be removed from their routing tables. A variation of route poisoning is split horizon with poison reverse whereby a router sends updates with unreachable hop counts back to the sender for every route received to help prevent routing loops.

Some Distance-vector routing protocols use a maximum hop count to determine how many routers traffic must go through to reach the destination. Each route has a hop count number assigned to it which is incremented as the routing information is passed from router to router. A route is considered unreachable if the hop count exceeds the maximum allowed. Route poisoning is a method of quickly removing outdated routing information from other router's routing tables by changing its hop count to be unreachable (higher than the maximum number of hops allowed) and sending a routing update.

In the case of the Routing Information Protocol (RIP), the maximum hop count is 15 so to perform route poisoning on a route its hop count is changed to 16, deeming it unreachable (sometimes referred to as an Infinite metric) and a routing update is sent.

When a router receives a route poisoning, it sends an update back to the router from which it received the route poisoning, this is called poison reverse. This is to ensure that all routers on a segment have received the poisoned route information.