Routing Algorithms????

So this is what the routing protocols are made up of mostly???

Im learing about routing algorithms and I think this is what makes up a routing protocols or how they work. I know some routing protocols contain more stuff such as other protocols but I think this is the general idea.

Routing Algorithms are composed of metrics that they used to function while Routing Protocols are composed of Routing Algorithms.

so i think it goes like this,

metrics

>Routing Algorithms

> Routing Protocols

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Comments

Webmaster

Yeah, that's pretty much it. A routing protocol is used to exchange address information of routed protocols. It is used to create a map with possible destinations. To calculate the best route to a destination, a routing algorithm is used. An algorithm needs values as input, in this case metrics. A metric value is assigned (often automatically, based on bandwidth for example) to each link between two routers (hops).

Alien

A routing protocol is used by a router to find the best path to a destination network. Examples include RIP, IGRP, OSPF, EIGRP, BGP etc.

A routing algorithm is the method used by a routing protocol to calculate the best path to a destination. Examples of routing algorithms are bellman ford which is used by EIGRP and Djikstra algorithm or shortest path fast used by OSPF.

Just my 2.cts

x_Danny_x

excellent! I am on the right track.

that last sentence, can that be applied to the RIP protocol? Cause it gives a number of hops (16 to be exact) to reach the destination or it drops it.

I know there is more towards RIP such as that split horizons that uses some other type of algorithm to do its calculation.

Webmaster

Yes, RIP uses hop count as its metric. This means that every router between the source and destination is a 'hop'. The next router is 1 hop away. The route with the least amount of hops is the route that the router will prefer (depending on several other things indeed, including administrative distance). This is not a very good approach, as it will prefer a 56k connection thru 2 other routers over a 1.5 MB frame relay link with three intermediate routers.

I posted some related info in this topic: www.techexams.net/forums/viewtopic.php?t=466

x_Danny_x

thanks Johan/Webmaster. I did went through all of that but didnt understood it much, the topics that werent cover on the Network+ I mean.

so OSPF protocol uses the Link State Algorithm and IGRP, EIGRP, & RIP using the Bellman/Distance Vector Algorithm like the poster Alien said.

gotcha!

Im going to review the technotes over again! Thanks!

EdTheLad

Hey Dannyx,
Just to let you know Rip has a 15 max hop count not 16.
16 means unreachable.

Alien

RIP and IGRP are distance vector protocols that use distance and direction to build a routing table. A major difference between them is that RIP uses hop count as cost while IGRP uses Bandwidth Reliability Load and Delay(some books say Bandwidth and Delay).

OSPF uses Djikstra algorithm which is based on cost and the state of a link. It uses a neighborship relational database which is used to store link state information about neighbors on the same network. It also has a topology database containing all the learned routes from other routers. It uses a SPF (shortest path first) algorithm to build a SPF tree with itself as route. The SPF tree is then used to fill up the routing table with the best paths to a destination network from the SPF tree.

EIGRP is a high breed routing protocol meaning it shares features from both link state protocols and distant vector protocols. This makes it the most complicated and most efficient of the lot. It is also the fastest convergence. EIGRP has qualities of OSPF in that it forms neighbor relationship with its neighbors. It uses a neighbour table, topology table and a routing table. EIGRP uses an DUAL (Diffusing Update Algorithm) to select the best routes(normally called a designated route) from the its topology table and places it on the routing table. EIGRP uses RTP (Reliable Transport Protocol) to ensure reliable communication with other EIGRP routers in an EIGRP topology. Another important aspect of EIGRP is its ability to support multiple protocols using a feature Protocol Dependent Modules. This enables EIGRP to route packets from routed protocols such TCP/IP, Appletalk, IPX/SPX. Each protocol uses its own PDM and EIGRP creates a separate routing table for each protocol.
Guess i better stop here before i doze off again or worse still get lost. I feel like i have overstepped my zone but i'm quite sure all these stuff are contained in Webmaster tutorial.

Bravo Webmaster for rectifying what could have been a confusing situation. Like you stated, a routing protocol is used by routers to share routing information which is used to build the routing table. My mistake, i must have been sleepy headed on my first reply since it was 2 hrs past midnight. Next time i'll be more carefull. This thread has got me so motivated after missing the CCNA twice with 815 the first time and 801 second time. It really put me off and i laid down my tools. Now i feel i'm back in the zone because of this thread.

Thanks Webmaster and goodluck x_Danny_x

Fu Loser

I Think of routing algorithms has complex math code for Routing Protocols to use.

EdTheLad

It's not complex at all, just read the RFC's and you will see everything explained there.

Alien

I agree that the theory is not that complex as such at the CCNA level. I made some typo error here which might make it seem so but the configuration and troubleshooting is a bit complex especially OSPF. The study guides cover this topic pretty well.

In response to FULoser: Its not scary at all once you capture the concept infact DUAL is a very interesting algorithm and so is SPF.

After many long hours infront of the screen, most of my close associates have been advicing me to pay the optician a visit and get meself some spectacles. I think its time i heeded their advice before something terrible happens on my CV.

Fu Loser

hehe cool.

Ill have to check out the RFC's