From: routerjocky (elouie@xxxxxxxxx)
Date: Mon Oct 15 2001 - 15:30:57 GMT-3
> All:
> Can someone please help me understand Frame Relay, physical
> and subinterfaces. What works with what?
Any can work with any at a Layer 2 perspective.
example - you have a hub router with two spoke routers and 2 PVCs, hub to
spoke1 and hub to spoke2.
The Hub can have a physical interface with a PVC configured to Spoke1 and a
subinterface with a PVC configured to Spoke2.
At Layer 3 different combinations of physical/subinterface require some
additional configuration. You actually touch on those your subsequent
questions.
> How do you decide to use either phycical, point to point or
> multipoint?
By knowing the topology that's being implemented. Using the same example as
above, if the Hub were to use only the full interface, that (by definition)
becomes a multipoint circuit. If the Hub were to use only one subinterface
to reach both Spoke routers, that would be a multipoint subinterface. It's
a design and implementation decision that one makes based on the
applications that will be travelling on the network and the topology within
the frame relay cloud. Review Caslow again - p 126 (1st Ed, Survey the
primary combinations) and perhaps draw them out yourself in addition to his
diagrams.
> Also, how do you know when to use map statements?
When you don't have a direct connection between sites and you need IP
connectivity between them, the most basic way to enable that (Layer 3)
connection is to use a map statement. Assuming no PVC between Spoke1 and
Spoke2, both spokes would need frame relay map statements to each other to
get basic IP connectivity between them.
Once a map statement is entered, inverse arp for that DLCI is disabled.
Thus, on the spoke router(s), if you enter ONE frame relay map statement,
you'd better enter the other frame relay map statement too (the map to the
hub). Otherwise, when the router is rebooted, inverse arp will be
disabled, and therefore the dynamic frame-relay map to the hub router will
not appear resulting in no IP connectivity to the hub.
> When do you use map statements vs. dlci command?
Re-Read p 121 (1st edition) The "frame-relay inteface dlci" statement. Is
there something specific in that section that do you not understand?
> I just got done with Caslow am somewhat confused trying to
> tie it all together?
>
> Thanks,
> Steve
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