From: Jim Brown (Jim.Brown@caselogic.com)
Date: Thu Feb 27 2003 - 12:47:46 GMT-3
Think about what split horizon is....
Split horizon basically keeps a router from advertising a route out the
interface it learned the route from. Most of the time this is the
desired behavior, but in the case of a multipoint interface it might not
be.
If the spokes are advertising routes to the hub and the hub has split
horizon enabled, it will not advertise routes from one spoke to another
if they are on the same interface.
Split horizon only affects DV protocols and to disable it for EIGRP you
must use a different command than other DV protocols. The command is no
ip split-horizon eigrp <AS> while all other DV protocols us the command
no ip split-horizon.
You can also use show ip interface to determine the status of split
horizon on an interface.
-----Original Message-----
From: Hunt Lee [mailto:huntl@webcentral.com.au]
Sent: Thursday, February 27, 2003 12:20 AM
To: 'ccielab@groupstudy.com'
Subject: Split-horizon mystery
Hi Group,
Does anyone know when one should use "ip split-horizon" for EIGRP?
RTD
/
RTA---- RTB
\
RTC
RTA, RTB & RTD are using OSPF, while RTA & RTC are both using EIGRP...
RTA & RTC are point-to-point, while..
RTA, RTB & RTD are point-to-multipoint
On the solutions, I was told that I need to use "ip split-horizon" on
RTC
outgoing interface (to RTA), why??? I thought we only need to use this
command on the hub if it is point-to-multipoint sub-interface...
anyway, here's the config:-
On RTC:-
interface Serial0
ip address 137.20.200.18 255.255.255.240
ip nat outside
encapsulation frame-relay
ip split-horizon <------ Do we need this???
no ip mroute-cache
keepalive 15
no fair-queue
frame-relay lmi-type ansi
router eigrp 10
network 137.20.0.0
no auto-summary
And on RTA:-
interface Serial0.1 multipoint
ip address 137.20.100.34 255.255.255.224
ip ospf network point-to-multipoint
frame-relay de-group 1 502
frame-relay map ip 137.20.100.33 502 broadcast
frame-relay map ip 137.20.100.35 503 broadcast
!
interface Serial0.2 point-to-point
bandwidth 2000
ip address 137.20.200.17 255.255.255.240
frame-relay interface-dlci 504
router eigrp 10
redistribute ospf 10 metric 2000 100 255 1 1500
passive-interface BRI0
passive-interface Ethernet0
passive-interface Serial0.1
passive-interface Serial1
network 137.20.0.0
no auto-summary
no eigrp log-neighbor-changes
Any help / ideas would be greatly appreciated.
Regards,
Hunt
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