From: Brian Postma (brpostma-gs@xxxxxxxxx)
Date: Tue Feb 06 2001 - 08:45:48 GMT-3
Oh yeah, I forgot about that. So I added "ip split-horizon eigrp 1" to both
routers (R1 & R2) and I still can't "see" the loop. All of the various show
commands and debugs do not seem to indicate that a loop is present. In the
debugs I have seen where R2 is advertising R5's Ethernet subnet to R1, but I
never see a "rcvupdate" on R1. Maybe I am not reading the debug properly.
The important thing here is to recognize what the default behavior of
split-horizon is and I had forgot that the split horizon rules for rip/igrp don
t
apply to EIGRP. I won't forget it anytime soon now.
But I am still confused that in "Hints for lab 2" under the "task three hints"
it clearly mentions split-horizon. Plus the solution shows the application of
the command "ip split-horizon" on Serial 0 of R2. As we have just seen that
command has no effect on EIGRP. I still would like to see why R1 is not
installing the R5 subnet route from R2? I have modified the admin distance of
external EIGRP so that it is better than OSPF but I still cannot get the looped
route into the routing table. I am missing something here. Any ideas?
brian postma
Justin Menga wrote:
> Rob,
>
> You are correct about split-horizon disabled on a frame physical interface
> by default - HOWEVER, this only applies to RIP and IGRP. To configure
> split-horizon for EIGRP you need to use 'ip split-horizon eigrp xx' and by
> default on ANY interface, split horizon for EIGRP is enabled.
>
> Regards,
>
> Justin Menga CCIE #6640 MCSE+I CCSE
> WAN Specialist
> Computerland New Zealand
> PO Box 3631, Auckland
> DDI: (+64) 9 360 4864 Mobile: (+64) 25 349 599
> mailto: justin.menga@computerland.co.nz
>
> -----Original Message-----
> From: Rob Webber [mailto:rwebber@callisma.com]
> Sent: Friday, 2 February 2001 6:57 a.m.
> To: 'Johnny Dedon'; 'Groupstudy'
> Subject: RE: CCIEbootcamp lab 2
>
> Router 2 is configured for EIGRP and is using Frame Relay without
> subinterfaces. Thus ip split-horizon is disabled by default. Thus everything
> r2 learns from R1 via EIGRP, it will turn right around and advertise back to
> R1. On a "hub" router you often need split-horizon disabled, but on a
> "spoke" router (like r2) you almost always want it enabled.
>
> In this case it could be very dangerous. If r1 redistributes OSPF into
> EIGRP, then advertises all of those EIGRP updates to r2, r2 will advertise
> them all back to r1. Since EIGRP has a lower distance than OSPF, r1 will
> prefer the EIGRP routes coming from r2 - even for networks connected to r5 -
> routing loop!
>
> Hope this helps, Rob.
>
> -----Original Message-----
> From: nobody@groupstudy.com [mailto:nobody@groupstudy.com]On Behalf Of
> Johnny Dedon
> Sent: Wednesday, January 31, 2001 8:02 PM
> To: Groupstudy
> Subject: CCIEbootcamp lab 2
>
> Can anyone help with an explanation as to why split horizon is an issue on
> router2? Its late and I'm sure I'm missing something...be gentle :)
>
> Johnny Dedon
> Senior Staff Consultant
> Exodus Professional Services
> johnny.dedon@exodus.net
> www.exodus.net
>
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