Please Heeeeelp me

Hi,
I will be crazy, I read in (CCNP BSCI Official Exam Certification Guide, Fourth Edition)

Page#64 the author said,
"If the querier does not receive a reply from each of its neighbors, it repeats the
query as a unicast to each unresponsive neighbor until it either gets a reply or gives up after
sixteen tries."

And in Page#70the author said,
"When queries are produced, the router changes to an active state and sets a timer (typically three minutes). If the timer expires before an answer comes back then the router is considered stuck in active."

My question is it is tries 16 attempts to get replay or waiting 3 minute to consider is SIA or both is different.

BR,
Auos

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Comments

Forsaken_GA

The 3 minute SIA timer is definetly correct, and one of the reasons why it's so important to design an EIGRP network properly and limit query range.

Keep in mind that EIGRP queries, unless properly contained, have a cascading effect. So Router A queries Router B which is connected to routers C and D which are connected to routers E,F,G and H,I,J. And nobody is going to reply back to the router that it heard the query from until all of it's other neighbors answer it.

So I think the first statement is also correct Let's say it gets all the way down to router Z, I believe that after the 16th unicast retry, Router Y will say screw it and return unreachable to the router that queried it. In the meantime, 3 minutes have passed since Router A put out it's initial query, and it says screw it, tosses the route into SIA and bounces it's neighbor relationship with router B

jason_lunde

Great explanation foresaken! Thanks

auos

Ok, but where is a hello message in this scenario. I mean if query message is start the message is postpone or what.

Forsaken_GA

hello messages should still be being sent as normal, otherwise, it'll send more routes into active. A router will bounce it's adjacency with a neighbor when the SIA timer expires simply because it doesn't trust a neighbor that doesn't answer it's queries

Forsaken_GA

after reading through the EIGRP section of TCP/IP vol.1, I think I can better answer this question now (it was bothering me) -

I think on page #64, the author chose the wrong word in using reply. The initial query is sent multicast, and should have received an ACK, but not necessarily a reply yet. So I think it'd be better said that if the initial Query isn't ACK'd, it will resend it unitcast 16 times, and if it still isn't ACK'd, it'll bounce the adjacency. If it doesn't receive the REPLY packet back 3 minutes after the query goes out, then it'll declare the route Stuck in Active and bounce the adjacency.

Hope that makes sense, someone correct me if I'm on crack.

auos

Forsaken_GA wrote: »

after reading through the EIGRP section of TCP/IP vol.1, I think I can better answer this question now (it was bothering me) -

I think on page #64, the author chose the wrong word in using reply. The initial query is sent multicast, and should have received an ACK, but not necessarily a reply yet. So I think it'd be better said that if the initial Query isn't ACK'd, it will resend it unitcast 16 times, and if it still isn't ACK'd, it'll bounce the adjacency. If it doesn't receive the REPLY packet back 3 minutes after the query goes out, then it'll declare the route Stuck in Active and bounce the adjacency.

Hope that makes sense, someone correct me if I'm on crack.

Great thanks for your helpful explanation, I think you are right.

adam-b

Forsaken_GA wrote: »

after reading through the EIGRP section of TCP/IP vol.1, I think I can better answer this question now (it was bothering me) -

I think on page #64, the author chose the wrong word in using reply. The initial query is sent multicast, and should have received an ACK, but not necessarily a reply yet. So I think it'd be better said that if the initial Query isn't ACK'd, it will resend it unitcast 16 times, and if it still isn't ACK'd, it'll bounce the adjacency. If it doesn't receive the REPLY packet back 3 minutes after the query goes out, then it'll declare the route Stuck in Active and bounce the adjacency.

Hope that makes sense, someone correct me if I'm on crack.

This is a perfect explanation...one that is not always spelled out well in the study guides.