Subject: Re: when to run in NBMA or P2MP mode?

From: "Naidu, Venkata" <[email-masked]>
Date: Thu, 3 Oct 2002 13:27:59 -0400

Dave,

-> From: Dave Katz [mailto:[email-masked]]
-> Sent: Thursday, October 03, 2002 12:52 PM
->
->    what exactly is the difference between p2p interfaces and
-> p2p subinterfaces.
->    I tried searching for that in google but couldnt find any
-> information. I
->    come across this term a lot of times and would be glad if
-> somebody could
->    explain me about it.
->
-> A subinterface (or logical interface) is a way of subdividing a
-> physical interface into multiple logical interfaces.

  Is this same as *multi-netting* ? I think there is a small
  difference between *multi-netting* and *subinterfaces*.
  Multi-netting can be applicable to BCs also (not only NBMAs)?!?

-> NBMA interface
-> are often treated this way--one or more PVCs is treated as a logical
-> interface.  If only one PVC is bound to a logical interface, that
-> logical interface can appear to the rest of the system as a standard
-> point-to-point interface.  You can also bind multiple PVCs and treat
-> it as a multipoint interface, but this is rarely done in practice.
-> Subinterfaces are often used with other media, such as VLANs--each
-> VLAN is treated as a separate multipoint subinterface.
->
-> From the point of view of router applications (such as
-> OSPF), there is
-> no difference between a true P2P interface and a P2P subinterface,
-> which of course is the whole point fo the exercise.

--
Venkata.

---

From: Dave Katz <[email-masked]>
Date: Thu, 3 Oct 2002 12:52:08 -0700

If by "multi-netting" you mean assigning multiple subnets to a
physical interface, this isn't necessarily the same.  The key to
subinterfaces is that an incoming packet must have sufficient
information to be able to demultiplex to the proper subinterface.  You
can't assign multiple subnets to an Ethernet, for instance, using
subinterfaces, because you can't tell by looking at an incoming packet
the interface with which it is associated.  (But you can if you are
using VLANs by looking at the VLAN ID, or on ATM or FR by looking at
the VC information.)