Re: EIGRP Basic DUAL rule

To answer your questions. With a multi-access interface like frame relay or
ethernet we can have multiple neighbors on a single interface. With the
interface command ip eigrp split-horizon (the default) enabled and if we
are receive an update from a neighbor on this interface we will not send out
an update to other neighbors on this interface. EIGRP split horizon is a
routing loop prevention mechanism. If we disable EIGRP split horizon then we
allow updates received on the interface to be sent back out the interface to
other neighbors. This is the reason why the poison reverse packet is sent
out to all neighbors if EIGRP split horizon is disabled. The reason for the
poison reverse to be sent when a new successor is chosen is to let the other
routers know to not use this router as a next hop for best path.

If you type the command show ip int "interface-name" you will see either
Split horizon is enabled or disabled. This is not for EIGRP this is for RIP.
To check if EIGRP split horizon is enable type show run interface
"interface-name".

Steve Lyons

On Sat, Aug 22, 2009 at 8:04 PM, Anantha Subramanian Natarajan <
anantha.natarajan_at_gravitant.com> wrote:

> Hi All,
>
> I am able to understand the delay infinity value.It seems that vector
> metric value of set to -1(minus 1) is infinity.Kinldy clarify the other
> part of the questions.
>
> Thank You
>
> Regards
> Anantha Subramanian Natarajan
>
> On Sat, Aug 22, 2009 at 6:45 PM, Anantha Subramanian Natarajan <
> anantha.natarajan_at_gravitant.com> wrote:
>
> > Hi All,
> >
> > I was going though the "EIGRP Network Design solutions" and have couple
> > of questions based on the below lines.Kindly help me to understand the
> same.
> >
> >
> > *Basic DUAL Rules*
> > *
> >
> > 1) Whenever a router chooses a new successor,it informs all its other
> > neighbors about the new reported distance
> >
> > 2) Every time a router selects a successor,it sends a poison update to
> > its successor(poison reverse)
> >
> > 3) A poison update is sent to all neighbors on the interface through
> > which the successor is reachable unless split-horizon is turned off,in
> which
> > case,it's sent to only the successor
> >
> > I am understanding that a posion update is a regular update with delay
> set
> > to infinity.What is that infinity value,is it the maximum delay value
> which
> > can be set on an interface (16777215 tens of microseconds)? .If that is
> the
> > case,why not the other parameters like bandwith is not set to maximum
> value
> > in the posion update.
> >
> > Also I am trying to undertstand,point 3 above,is the posion update
> depends
> > on the split-horizon enabled on the interface.
> >
> > Kindly clarify the above.Thanks for the assistance.
> >
> >
> >
> > Regards
> >
> > Anantha Subramanian Natarajan
> >
> >
> >
> >
> > *
> >
> > **
>
>
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Received on Sat Aug 22 2009 - 21:40:35 ART