Judging by the web page on Cisco's site
(http://www.cisco.com/warp/public/779/smbiz/service/knowledge/wan/subifs.htm),
it appears as if split-horizon is disabled for routing IP on physical
(multipoint) interfaces as well as multipoint subinterfaces.
Here's the part I'm referring to:
"Note: For TCP/IP, Cisco routers can disable split-horizon limitations on all
frame relay interfaces and multipoint subinterfaces and do this by default.
However, split-horizon cannot be disabled for other protocols like IPX and
AppleTalk. These other protocols must use subinterfaces if dynamic routing is
desired."
Out of curiosity, what is it that leads you to believe that split-horizon is
enabled on frame relay subinterfaces?
-- Leigh Anne
> -----Original Message-----
> From: Brian Lodwick [mailto:[EMAIL PROTECTED]]
> Sent: February 27, 2001 1:45 PM
> To: [EMAIL PROTECTED]; [EMAIL PROTECTED]
> Subject: RE: FR + Poison Reverse...
>
>
> Leigh Anne Chisholm,
> Actually by default on IP interfaces:
> Split-horizon is disabled on Frame-relay physical interfaces
> Split-horizon is enabled on Frame-relay point-to-point and multipoint
> subinterfaces
> (but who cares it's configurable)
>
> There is a difference between a multipoint physical interface and a
> multipoint subinterface. Althought there aren't too many
> differences (static
> mapping and dynamic mapping allowed on both) there are subtle differences.
> My brother and I went over this yesterday and wondered what the differences
> are. What we came down to was that the big difference is simple
> -subinterfaces function is to provide a means to logically separate a
> physical interface. The subtle differences like the default split-horizon
> setting and default OSPF network type aren't the big differences. You can
> build a fully scaleable hub spoke frame model using a physical multipoint
> interface on the hub and point-to-point subinterfaces on the spokes. The
> advantage of using the Multipoint subinterface on the hub? You would only
> need 1 physical interface for 2 hub spoke frame models. I am interested in
> learning more about other things you can do with the hub as a multipoint
> subinterface to control traffic, such as for filtering or traffic shaping.
>
>
> >>>Brian
>
>
>
>
> >From: "Leigh Anne Chisholm" <[EMAIL PROTECTED]>
> >Reply-To: <[EMAIL PROTECTED]>
> >To: "Brian Lodwick" <[EMAIL PROTECTED]>, "Cisco@Groupstudy. Com"
> ><[EMAIL PROTECTED]>
> >Subject: RE: FR + Poison Reverse...
> >Date: Tue, 27 Feb 2001 12:41:07 -0700
> >
> >Whoops! When I posted Excerpt 1, I missed the part in the first sentence
> >that
> >seems to imply that frame-relay interfaces and multipoint interfaces
> >disable
> >split-horizon BY DEFAULT (when using TCP/IP).
> >
> >When I took ICRC so many years ago, I remember discussing split-horizon but
> >don't recall any explicit mention that split-horizon is disabled by default
> >for the IP routing protocols (RIP and IGRP). I remember discussing this
> >issue
> >as well in CIT but I don't think the exception to the rule was noted
> >either--but because I wasn't aware of it, it may have been something that
> >went
> >in one ear and out the other.
> >
> >It's interesting to note that in the current ICND curriculum, I know the
> >section that talks about configuring subinterfaces indicates that
> >"multipoint
> >subinterfaces act as NBMA network so they do not resolve the split horizon
> >issue". I don't have the entire official ICND curriculum available, but I
> >don't notice anything specifically mentioning the exception.
> >
> >So, in summary - we're both right with respect to multipoint interfaces:
> >
> >With multipoint (or physical) interfaces: split horizon is ENABLED by
> >default
> >unless you are routing IP across the link. Then it is DISABLED. If you're
> >routing using RIP, IGRP, or EIGRP to route IP, it's DISABLED. If you're
> >routing IPX using RIP, EIGRP, NLSP, it's ENABLED. It's also enabled if
> >routing AppleTalk.
> >
> >With point-to-point subinterfaces, split horizon is ENABLED but isn't much
> >of
> >an issue since it's a point-to-point link.
> >
> >
> > -- Leigh Anne
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