NHRP questions

[David Horton <[e-mail]>]

I have been away from the discussions for longer than I would like and 
have a few questions about the NHRP draft <draft-ietf-rolc-nhrp-IV.txt>

(a) Is NHRP intended to replace rfc1735 NBMA Address Resolution Protocol (NARP)?

(b) If not, how are the overlaps and incompatibilities between them resolved?
    i.e. they use the same IP protocol number, but the formats differ.

(c) Why are packets encapsulated in IP?
    My understanding is that the packets are encapsulated in IP packets
    with protocol type 54 (c.f. 1-ICMP, 6-TCP, 17-UDP etc).
    The ATMARP in rfc1577 (Classical IP and ARP over ATM) uses AAL5 directly
    with an ether type 0x08-06 (c.f. IP 0x08-00).

    What is the IP encapsulation providing the protocol? 
    - an easier implementation for those with IP
    - a way of identifying the source (since there is no source HW address?)

    On the downside it would seem to make things difficult for other protocols.
    (Wouldn't another protocol implementation, e.g. IPX(?), have difficulty 
    with just entering the IP addressing space?)

    Are there reasons why rfc1483 encapsulation isn't used?
    Could NHRP be implemented as extensions to ATMARP instead?

(d) How IP masks registered?
    I am confused as to how a edge router can register with the NHS that
    it acts as a gateway to other IP networks. I presume it would have to
    be via the NHRP register.
    In addition, the NHRP MIB <draft-ietf-rolc-nhrp-mib-00.txt> has an IP mask
    attribute in the NHRP address table, nhrpAddrDestNetMask. How would
    this be filled in from the protocol supplied information?

    Does NHRP need an extension (IP specific) to specify the net mask 
    associated with the source IP address?

(e) What documents exist at the moment that specify the routing functionality
    of NHRP?
    Does an NHS (server mode) just look up its own IP routing tables
    and apply those entries to the incoming NHRP requests?

(f) Why aren't the NBMA addresses as richly defined as those in ATMARP?
    My understanding from rfc1577 is that the ATM addresses in ATMARP are
    defined to contain type and length fields for ATM number and subaddress,
    effectively 6 fields (although type and length are merged so they
    only take 1x8 bit field, so actually only 4 fields).
    In NHRP, there is only the type, length and address field (i.e. 3 fields).
    Why isn't the subaddress needed?
    Is there a document describing the addressing that I need to read?

(g) Is there a need for InARP with NHRP?

(h) How does an end system or intermediate system get in contact with the NHS?
    My understanding is that each ES and IS is specially configured with
    IP address of its designated NHS. Wouldn't that imply that you would
    need a special config file (or other mechanism) just for NHRP, 
    i.e. a file like /etc/nhrp?
    Are there other options like:
    - a well known IP address in the reserved IP address range > 240.0.0.0
    - a well known permanent IP multicast address in the
      reserved IP address range > 224.0.0.0
    - a well known name that resolves to the NHS, 
      e.g. via /etc/hosts or name serving
    - a well known ATM address


Does that expose my degree of confusion?

regards,
David

 David Horton
 Centre for Information Technology Research
 University of Queensland, 4072        Australia
 Email: [e-mail]         Phone [phone]   Fax [phone]