From: OhioHondo (ohiohondo@columbus.rr.com)
Date: Fri Feb 28 2003 - 17:31:00 GMT-3
Brian
Just for my own clarification I'm going to try to summarize what I think is
your input on this string -- and maybe ask for a clarification.
Split Horizon is only applied at the interface level.
The setting of split horizon is specific to the interface or sub-interface
on which it is applied.
Split Horizon is only used with IGP's (RIP, IGRP, EIGRP).
Split Horizon only applies to routing updates.
Both RIP/IGRP and EIGRP Split Horizon are on by default.
There are two types of Split Horizon.
RIP and IGRP use the interface command "ip split-horizon".
EIGRP uses the command "ip split-horizon eigrp XXX"
It is not clear as to whether both of these can co-exist on the same
interface but since you can run RIP and EIGRP on the same interface it is
logical that you can.
You can monitor the setting of split horizon for RIP or IGRP using "sho ip
int". If you config "no ip split" it shows up in the config file.
I don't believe anyone has come up with how we can monitor the setting of
split horizon for EIGRP. If you config "no ip split eigrp XX" it shows up in
the config file.
Split Horizon should probably only be disabled on interfaces that are hubs
to two or more spokes. If it is not disabled, routing updates from one spoke
will not be propagated to the other spokes.
-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com]On Behalf Of
Connie Nie
Sent: Friday, February 28, 2003 10:14 AM
To: ccielab@groupstudy.com; 'brian@cyscoexpert.com'
Subject: RE: Split-horizon mystery
Brian,
Can you elaborate a little bit on the effect of IP split-horizon and eigrp
split-horizon if used together? If I have a hub interface with ip
split-horizon enabled but eigrp split-horizon disabled, then the routed
traffic will observe split-horizon rule but routing traffic will not---do I
understand it correctly? If that is the case then the spoke will have a
route for the other spoke, but won't receive any traffic from the other
spoke. I guess my question is how do these two work together?
Thank you very much.
Connie
-----Original Message-----
From: Brian McGahan [mailto:brian@cyscoexpert.com]
Sent: Friday, February 28, 2003 1:11 AM
To: 'OhioHondo'; 'Brian Dennis'; 'Hunt Lee'; 'Jim Brown'
Cc: ccielab@groupstudy.com
Subject: RE: Split-horizon mystery
IP split horizon and EIGRP split horizon are independent of each other.
EIGRP split horizon is always on unless you disable it. You can disable
IP split horizon, and leave EIGRP split horizon on, and vice versa.
As Brian mentioned, sub-interfaces count as different logical entities,
so you could have IP or EIGRP split horizon disabled on one and enabled
on the other. To check if IP split horizon is on, use the 'show ip
interface [int]' command.
HTH
Brian McGahan, CCIE #8593
Director of Design and Implementation
brian@cyscoexpert.com
CyscoExpert Corporation
Internetwork Consulting & Training
Toll Free: 866-CyscoXP
Outside US: 847.674.3392
Fax: 847.674.2625
> -----Original Message-----
> From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf
Of
> OhioHondo
> Sent: Thursday, February 27, 2003 9:40 PM
> To: Brian Dennis; 'OhioHondo'; 'Hunt Lee'; 'Jim Brown'
> Cc: ccielab@groupstudy.com
> Subject: RE: Split-horizon mystery
>
> Brian
>
> Do you know how to check if EIGRP Split Horizon is set?
>
> It is possible to set split horizon and ip eigrp split horizon
separately.
>
> Setting split horizon seems to manipulate the value shown in "sho ip
int".
>
>
> -----Original Message-----
> From: Brian Dennis [mailto:brian@labforge.com]
> Sent: Thursday, February 27, 2003 9:25 PM
> To: 'OhioHondo'; 'Hunt Lee'; 'Jim Brown'
> Cc: ccielab@groupstudy.com
> Subject: RE: Split-horizon mystery
>
>
> Normally you aren't processing IP on the major interface if you are
> using sub-interfaces so anything relating to split-horizon on the
major
> interface has nothing to do with the sub-interface.
>
> Rack4R3#sho ip int | include (Serial)|(Split)
> Serial1/0 is up, line protocol is up
> Serial1/0.32 is up, line protocol is up
> Split horizon is enabled
> Serial1/0.243 is up, line protocol is up
> Split horizon is enabled
> Rack4R3#sho ip int s1/0
> Serial1/0 is up, line protocol is up
> Internet protocol processing disabled
> Rack4R3#
>
> Brian Dennis, CCIE #2210 (R&S/ISP Dial/Security)
> brian@labforge.com
> http://www.labforge.com
>
> -----Original Message-----
> From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf
Of
> OhioHondo
> Sent: Thursday, February 27, 2003 5:36 PM
> To: Hunt Lee; 'Jim Brown'
> Cc: ccielab@groupstudy.com
> Subject: RE: Split-horizon mystery
>
> Hunt/Jim
>
> I believe that split horizon on an interface works for the entire
MAJOR
> interface. If you have applied split horizon applied to an interface
it
> applies to all of the sub-interfaces on that MAJOR interface.
>
> I know that you can apply "ip split eirgp xx" directly on a
> sub-interface,
> but does it then only apply to that sub-interface?
>
> -----Original Message-----
> From: nobody@groupstudy.com [mailto:nobody@groupstudy.com]On Behalf Of
> Hunt Lee
> Sent: Thursday, February 27, 2003 6:10 PM
> To: 'Jim Brown'
> Cc: 'ccielab@groupstudy.com'
> Subject: RE: Split-horizon mystery
>
>
> Hi Jim,
>
> That's kinds of fall into what I was thinking... hence the answer to
my
> lab
> scenario would be wrong?? Since the EIGRP is only running on a
> point-to-point network here?
>
> Or am I completely off?
>
> Thanks in advance,
>
> Regards,
> Hunt
>
>
> -----Original Message-----
> From: Jim Brown [mailto:Jim.Brown@caselogic.com]
> Sent: Friday, 28 February 2003 1:48 AM
> To: Hunt Lee; ccielab@groupstudy.com
> Subject: RE: Split-horizon mystery
>
>
> 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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