the next topic of discussion is the Cisco Proprietary Protocol
enhanced interior Gateway Routing protocol R E i G R P For short
now E i. G R P is an advanced distance vector routing protocol.
especially the older ones. If you read them, it will say that the a G R P. Is a hybrid protocol, insinuating that it's partly dis inspector and partly Link state. That is absolutely incorrect.
So that might have been a marketing ploy by Cisco to say that. Okay, you get the best of both worlds. But that is not the case. Yes, J. R. P is a distance vector routing protocol. However you can say that yes, it is an advanced distance vector routing protocol.
Why is it in advance this in vector routing protocol? Because E I G R P updates are non patriotic, partial and bounded.
So what do I mean by non periodic well
with route information? Total call. The routing update, which was the whole routing table, will sense every 30 seconds.
Yeah, J. R P does not send its updates every 30 seconds or every set Interval e J R B only sends an update when something in the topology changes, a new writer link comes up or a rattling goes down.
That's the only time and update descent.
The next word I use was the updates, uh, partial, which means the contents of the whole routing table is not sent to my directly connected devices.
On Lee, the change in the network is sent,
not the whole routing table. So if a link goes down, I let my neighboring rather know that this this link went down. I won't send the whole routing table over because that's not needed.
Next, I said, the updates are bounded. Bounded means the updates are sent on Lee to neighboring devices that need them not to everybody, which makes it more efficient. Hence, it is an advanced this inspector routing protocol.
Yeah, Jarvi updates are sent to the multi cast address to 24 00 10
now since abates a non periodic. You don't know if your neighboring router went down at some point. So to counter that, yes, you are the uses little packets called hello packets to keep the link alive and to discover directly connected devices. So if I receive e g r P, hello
forma directly connected device. I know that device is alive
and I can discover that it's actually there. I have a neighbor that also speaks E g R P.
is held the whole time
for the neighbor. When I send a hello packet to Annie I g r P neighbor within it, I will set the whole time.
The whole time is the number of seconds. My neighbor is supposed to wait for me to send another helo or update packet before considering me down.
The whole time is usually set to three times the hollow interval
by default. The whole time it's set. Do three times the hello interval.
So for links speeds greater than t one speeds with it which is 1544 kilobits per second. A lose are sent every five seconds.
So the whole time for links speed that is greater than three t one speeds. The whole time will be 15 seconds. Three times the hello interval
fooling speech less than t one speech or less than 1544 kilobits per second.
The hello timer is set to 30 seconds so my whole time is
three times three is 9 90 seconds on my hello time would be 30 seconds
He has your P stores, all routes to all destinations in a table called the topology table. So all routes stored
are stored in the topology table, even if multiple routes to the same destination. In case I have multiple links to the same destination President, even multiple routes to the same destination are stored in the topology table.
Now these routes, as they sit in the topology table, are called feasible successor routes.
One point backing up for a minute is all these routes are stored in the topology table and the topology table exchange occurs after I have discovered my neighbors threw the hello message. So when I send my neighboring router Ah, hello and I receive Ah, hello. Back from my neighboring router.
I will go ahead and exchange the contents off my topology table
with my neighboring router so that he learns all the routes to or that it learns all the routes to
Now, as these routes sit in the topology table, they're called feasible successor routes.
So these route, as they're reciting the topology table, they're called feasible successor routes.
Each one of these routes has an associate ID metric, and the metric for E. I. G R P is called the feasible distance.
I will go into more. About what? How the metric for years, every works in about five minutes. But the metrics for AARP is called feasible Distance.
I said that all the routes to all the destination, even multiple routes to the same destination are stored in the topology table.
The best one of these routes. The best one off each of these routes is plucked from the topology table and implanted in the I P routing table or you're out information base. And then it is called the successor route.
So which is the best route
off all the routes in the topology table, while the best routes will be the one with the Louis Metric or the Louis feasible distance, So the route with the Louis feasible distance is plucked from the topology table and implanted in the route information base or your routing table,
and then it can be used
now. E. A G. R P also has a concept called reported distance.
Now be advised that if you're reading a book on me as your piece. Some of the older books called this the advertised distance. The newer book Now books have now started calling it the reported distance. Now what is the reported distance?
The reported distance.
the feasible distance for your upstream router
and what does that mean?
Well, let's look at this topology router. One is connected to a router to, and rather too, is connected to a router. Three. Network 10 at the very end is available to router to and router one through router tree,
router to is a feasible distance off 50 away from Network 10 or from router three.
So that is router two's feasible distance Now router to reports a distance off 52 router one.
So Router one will see a reported distance off 50 because router to is reporting its own distance, the router one as being 50
router. One will take that 50 and daughter one knows that its own distance from itself to router to is 100 it will add the 50 to 100 to get a total feasible distance off 1 50
So once again, a reporter distance is the distance and upstream or closer to the network that you were trying to get to an ops team. Router reports to you. So the feasible distance of the upstream router. As reported to you
now the next concept in yeah g r p I'm gonna cover is the feasibility condition.
The feasibility condition say's that a route reported distance must be less than the routes
feasible distance for it to be eligible to be installed in the topology table. So a route reported distance must be less than the routes.
Feasible distance for the route to be reported to be installed in the topology table. Let's see how this works.
We have three routes
between Router four and Router five. Let's create Network 10 over here, So Router four has passed a, B and C to choose out of to go from Router four to Network 10.
So path is to router. One path be is to router to and patsies to router three.
So let's calculate the feasible distance off this route.
Router one is reporting a distance or sending a reporter distance off. 32 out of four and the distance from writer for
to router one is 50. So the total distance for Path A is 80
router to is reporting a distance of 92 out of four,
and Router four has a distance of 10 from itself to router to for a total distance of 100.
Router three is reporting a distance off 72 Router four
and router fours. Distance from itself to rather three is 40
for a total distance off
So Path A becomes your successor out with a feasible distance,
an F B off 80 will pass. Be even make it to the topology table. Well,
my feasible distance is 80
and the feasibility condition states that my reported distance must be less than my feasible distance for the route to be installed in the topology table. Over here, Router to is reporting a distance off 90
two out of four, which is higher than my feasible distance.
So path be won't even be considered for installation in the apology table. Why is that Well, in effect, router to is telling router for that I'm further away from you
to get two out of five so router to is telling router. For that, I'm even further from router five than you are
because it is reporting a distance of 90 basically telling router for actually, I'm further away from your destination than you are.
So if Router four tries to route to router to and if you pick router to up and make it, put it further away from now or four. Rather four might send information to route her true and then have to pass back through itself.
Do you get to Network 10
which would cause a rounding loop So the feasibility condition is a new prevention mechanism,
So on the diagram, it might look like this, but in effect, router to is actually further away from Network 10. Then router, for
this could show up as a test question.
Now let's look at the last route,
even though the total distance
then path be. Patsy's total distance has won 10 pat bees. Total distance is 100 but the reported distance
that Router three is reporting
to router 4 70 which is less than your feasible distance. So patsy goes into the topology table and it is your feasible successor out
now. If the successor out fails, which is Path E. The next best feasible successor, which is Patsy, immediately becomes the successor,
which helps with convergence because you already have alternate paths to the same destination stored in your apology table. So if the best path fails, you immediately promote the next best path to the routing table.
This concludes the feasibility condition lecture.