From: Brian McGahan (brian@cyscoexpert.com)
Date: Fri Feb 28 2003 - 18:16:30 GMT-3
You got it. In addition to hub and spoke configurations, split-horizon
has an effect on how a router running RIP and IGRP behaves with
secondary addressing. See this document for more info on that
situation:
http://www.cisco.com/en/US/tech/tk648/tk365/technologies_tech_note09186a
0080093fdd.shtml
HTH
Brian McGahan, CCIE #8593
Director of Design and Implementation
brian@cyscoexpert.com
CyscoExpert Corporation
Internetwork Consulting & Training
Toll Free: 866.CyscoXP
Fax: 847.674.2625
> -----Original Message-----
> From: OhioHondo [mailto:ohiohondo@columbus.rr.com]
> Sent: Friday, February 28, 2003 2:31 PM
> To: Connie Nie; ccielab@groupstudy.com; brian@cyscoexpert.com
> Subject: RE: Split-horizon mystery
>
> 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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