Different sites have different answers to these questions: What helps speed up convergence? answer is "Triggered updates" Then somewhere it says "Route poisoning (used with holddowns) speeds up convergence. Because neighbors dont have to wait 30 sec. I understand both the questions but what i am afraid of is if i get something like the above questions in the actual exam I might do it wrong because they both say "speed up convergence" can somebody explain the 2 apart so i would not make a mistake incase? Thanks

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Tulip and others you can help and are in need of the convergece in the mind.

Convergence and loop avoidance according to Odom

Route poisoning
" is another method to help avoid loops and speed up convergence"

"unfortunately, some well known TCP/IP references have used these terms in different ways, making things a mess"

"Route poisoning is different than poison reverse"

(The typical description in the Cisco context follows) When a Distance vector routing protocol notices that a route is no longer valid, it has 2 choices
1.quit advertising about the subnet
2.Advertize that route, but with an infinite metric (is this not holddown?)

Route poisoning calls for the second of the two options, which removes the ambiguity about whether the route is still valid.

"One final loop prevention that also speeds up convergeance is calles Flash Updates, better known as Triggered Updates" When a router notices a subnet has changed state, it immediately sends another routing update on its other interface rather than waiting on the routing update timer to expire (is this not holddown timer, "better metric"). This causes the information about the route whose status has changed to be forwarded faster and starts the holddown timers more quickly.

"Split horizon with poison reverse, or simply poison reverse, is similar to split horizon"
I don't' know but I think this phrase stinks!

As we all know the Split Horizon does not allow a route that was learned through an interface to be readvertized out that interface.
Split horizon defeats counting to infinity problem over a single link.
Holddown timers resolves the counting to infinity problem when networks have multple paths to many subnets.Split horizion does not solve counting to infinity in all topologys. An addtional solution is required
Holddown timers
Route posioning (a routing update feature)

Could some one paraphrase this, maybe an anology.

Or the simple answear is Cram Exam
Routing Protocols
Convergence occurs when all routers in an interwork agree on optimal routes. A loop occurs when a packet bounces back and forth between two or more routers. A routing loop is sometimes called " count to infinity" Counting to infinity is a problem for distance vector routing protocols. It can be eliminated or mitigated by useing the following techniques
Max hop count-RIP 15,16 INFINITY
Split horizon- No readvertizing back out interface/ single link
Route poisoning- advertises the route, but with an infinite metric
Holddown timers-1.it expires
2. Infinity is finally defined as some max. #
3. Another update is received indicating the original route to the
network has been restored."
I need to see with better eyes
Thanks in advance
Sea******out*******

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quote:

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Originally posted by Sea Dragon:
<snip>
Or the simple answear is Cram Exam
<snip>
2. Infinity is finally defined as some max. #
<snip>

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The three holddowns are not from Cram Exam "the 1 out of the 3 questionable ways that holddowns are used", it says that holddowns are part of the loop resolution (stablization of vector protocols)
Here is what Cram Exam says
" A hold down timer indicates that no updates to a paticular route should be accepted until the timer expires.A hold down is triggerd when a router recieves an update from its neighbor indicating that reachable network has just gone down. The oruter marks the route as unreachable and starts its holddown timer.Whet the timer is active no updates are ignored. Updates about the unreachable network are only accepted from the neighboring router that initially indicated the unreachable network while the timer is active. If the neighboring router inticates that the network is reachable again, the router stops the hold down timers and updates its routing table. When the hold down timer expires, the router marks the network reachable and recieves updates from any router".
Also "Route posioning works well with holddown timers"

You may be right about the " infinity is a max #"
because by definition from Odom
"infinte is not a number, it is a concept"

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[This message has been edited by haubest (edited 01-09-2001).]

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