From: Narbik Kocharians (narbikk@gmail.com)
Date: Thu Jul 03 2008 - 17:09:38 ART
Before we go into the explanation remember that the queries by default are
set to 3 minutes and can be modified by "timers active-time" this can be
increased or decreased or totally disabled.
Now back to what you were asking, Let's say:
RA is connected to RB and RB is connected to RC, RA is advertising network
1.0.0.0 /8.
"SIA-Queries" and "SIA-Replies" are two new features that Cisco recently
added as an extra TLV in Eigrp packets and the beauty is that you don't need
to configure anything for this feature to be available and it's on by
default starting IOS 12.1 something.
In IOSes prior to 12.1, if RA lost network 1.0.0.0/8 and it had no feasible
successor, RA would send a query for network 1.0.0.0 /8 to RB. RB has no
entry for this network, so it would send a query to RC.
If there was a problem on the link connecting RB to RC, the reply packet
from RC will never get to RB, and as a result of that RA assumes that
because RB did not response in a timely manner (3 minutes by default, and
can be changed using the "timers active-time" command in the sub-router
configuration mode) it must be down. Therefore, RA will tear down the
adjacency to RB.
Now, with this new feature, RA sends a query down to RB (A SIA-Query) at the
midway point of the active timer which is 1.5 minutes (If default values are
used), and RB responds with a SIA-Reply, and once RA receives the SIA-Reply,
RA will know that RB is up and therefore, it does not tear down the neighbor
ship.
What happens down stream between RB and RC is as follows:
RB will send up to three SIA-Query to RC, if it does not receive a response
back from RC, it will tear down their adjacency and it will immediately
notify RA that it has no clue about network 1.0.0.0 /8.
Note, the adjacency between RA and RB is still up.
I hope this helped.
On Thu, Jul 3, 2008 at 10:08 AM, Ashwani ranpise <ashwani.ranpise@gmail.com>
wrote:
> Hello ,
>
> Can someone explain EIGRP query & reply process?
>
> 192.168.1.0/24 & 192.168.2.0/24----R1---R2---R3----R4----R5
>
> 1) What if link between R3 & R2 failed ? How many query & reply R4 & R5
> will
> get & for which routes (assuming no summary on R3)
> 2) What if R3 is summarizing those routes & sending it to R4 & link failed
> between R3 & R2?
>
> I was going through this document but couldn't understand.
>
> http://www.cisco.com/en/US/tech/tk365/technologies_white_paper09186a0080094cb7.shtml
> Any help will be useful for me.
>
> Thanks,
> Ashwani
>
>
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-- Narbik Kocharians CCSI#30832, CCIE# 12410 (R&S, SP, Security) www.Net-Workbooks.com Sr. Technical Instructor
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