From: Przemyslaw Karwasiecki (karwas@xxxxxxxxxxx)
Date: Sun Jul 28 2002 - 09:25:25 GMT-3
Quote from cisco documentation (both RIP and IGRP) :
"For all interfaces except those for which either Frame Relay
or Switched Multimegabit Data Service (SMDS) encapsulation is
enabled, the default condition for this command is ip split-horizon;
in other words, the split horizon feature is active.
If the interface configuration includes either the encapsulation
frame-relay or encapsulation smds command, then the default is
for split horizon to be disabled."
In the normal circumstances (e.g. no loops in the topology),
routes "backfired" via IGRP or RIP will have increased metric,
so they will not be accepted back:
(RouterA)-----------------------------(RouterB)
1. n hops to a.b.c.d ---[hop++]--> n+1 hops to a.b.c.d
2. n+2 hops to a.b.c.d <--[hop++]--- n+1 hops to a.b.c.d
But beware strange things which will happen while doing
redistribution between different protocols on RouterA.
In such case you prettty much ignore metrics, so everything
can happen.
PRzemek
On Sun, 2002-07-28 at 03:10, steven owen wrote:
> on p-to-p fr lines ,which runs rip ,i think i should
> enable ip split-horizon (which is disable default),or
> route loop may appear .but if runs ospf,it seems
> unnecessary.
> so is "ip split-horizon "necessary only on rip&igrp
> routing network?
>
> Thanks
>
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