From: McLaughlin, Jeffery (JMcLaughlin@sfchronicle.com)
Date: Thu Dec 23 2004 - 18:20:22 GMT-3
"Ok....so if you have a point-to-point subinterface, you specify the
dlci with the 'frame-relay interface-dlci xxx' command."
You have to use that command with *any* subinterface. Otherwise the router
doesn't know which DLCI's belong to the sub-if, and will assign them to the
physical interface, even if you're not using it. Remember, if a router has
ten subinterfaces and ten DLCI's, how does it know which DLCI goes with which
subinterface?
"By using the frame-relay interface-dlci command, aren't you relying on
inverse-arp,
and hence dynamic mapping, to give you the ip address of the other end of the
link?"
Not really. The frame-relay interfacace-dlci command just tells the router
which DLCI's (or PVCs) go where. It doesn't enable or disable inarp. For
example, you could have a physical interface only, which does not require a
frame interface-dlci statement, but it would still use inarp by default.
"If a requirement is to not use dynamic mapping, wouln't you have to change
that interface
type to multipoint so that you can disable inverse-arp and put in a specific
map statement?"
Nope. If the requirement is not to use a dynamic mapping, you could either
(a) use a p2p subinterface or (b) use frame-relay map statements (either under
the physical interface or the multipoint sub-if.) Using frame-relay map
statements disables inverse arp for that protocol.
HTH,
Jeff McLaughlin
CCIE #14023
-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of Kurt
VanDerMark
Sent: Thursday, December 23, 2004 1:08 PM
To: ccie2be; ccielab@groupstudy.com
Subject: RE: Frame Relay Questions
Ok....so if you have a point-to-point subinterface, you specify the
dlci with the 'frame-relay interface-dlci xxx' command. You cannot use
frame-relay map statements with a point-to-point subinterface.
By using the frame-relay interface-dlci command, aren't you relying on
inverse-arp,
and hence dynamic mapping, to give you the ip address of the other end of the
link?
If you show your frame-relay map, won't this result in a dynamic entry?
If a requirement is to not use dynamic mapping, wouln't you have to change
that interface
type to multipoint so that you can disable inverse-arp and put in a specific
map statement?
I hope I'm not splitting hairs here...
-----Original Message-----
From: ccie2be [mailto:ccie2be@nyc.rr.com]
Sent: Thursday, December 23, 2004 10:51 AM
To: Kurt VanDerMark; ccielab@groupstudy.com
Subject: Re: Frame Relay Questions
Kurt,
I'll tackle your question about inarp.
This is how I understand it.
By default, inarp is enabled and so is LMI.
LMI is a managment protocol that runs between the router and the switch -
it's local to that link.
There are 3 "versions" of LMI and you don't have to run the same version at
each end of the pvc.
What LMI does is announce to the router what pvc's (dlci's, really) are
active on the interface.
Once the router knows what dlci's are active, the router can inarp on each
dlci. This means the
router is asking for the remote router's Layer 3
address. (Note, I said Layer 3 address, not ip address because the same
process can work for clns or ipx I believe).
When you disable inarp, you disable the either the asking for or responding
to portion of the inarp process - I always forget.
But, the result is the same. If inarp is disabled throughout, you
effectively disable dynamic mapping.
HTH, Tim
----- Original Message -----
From: "Kurt VanDerMark" <kvandermark@highpoint.com>
To: <ccielab@groupstudy.com>
Sent: Thursday, December 23, 2004 8:39 AM
Subject: Frame Relay Questions
> I'm doing a little frame relay review, trying to make sure I nail down the
basics...and I have a few questions.
>
> Please correct anything I say that's wrong...
>
> I understand frame relay can be configured on an interface 3 ways:
> - physical interface (considered multipoint)
> - subinterface point-to-point
> - subinterface multipoint
>
> Say for instance I have a connection going from one router defined as a
physical interface, to another router defined via a subinterface. To avoid
routing issues such as interface mismatch with IS-IS (any other issues or is
this the only one?), I'll want to define the subinterface as multipoint.
If the other end of the connection is defined by a physical interface, why
wouldn't I always define the subinterface end as multipoint? If you aren't
worried about routing issues, is there some advantage to defining that end
as point-to-point?? Are there some split-horizon issues?
>
> Also, as a best practice, I understand its best to disable inarp on an
interface if you plan to use map statements before bringing the interface
up. If you don't plan to use map statements, and want to use dynamic
maps, does the FR switch just notify the router about all the mappings it
knows about, or does the service provider do filtering on the switch, or how
does that work?
>
> Sorry if these are basic questions, but I want to make sure I have this
down...
>
> Thanks.
>
> _______________________________________________________________________
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