Re: HIP, the Host Identification Protocol

[Paul Francis--formerly Tsuchiya <[e-mail]>]

>  
>  (This proposal was generated out of the genuine frustration of having
>  too many times asked officemates what subnet a particular cable
>  belonged to, and hearing in reply, ``Well, plug something into it and
>  see if it works.''  There is no need for Pip to perpetuate this
>  problem.)

If this is the main problem, then the need for such addressing
goes way down with Pip.  Since it will have auto-address configuration,
this question won't need to be asked.  Just plug in the host and
off it goes.......

I recognize the potential benefit for routers to make
local decisions about this LAN or that LAN to reach a
destination, but at the time being don't consider this to
be a major consideration.  I still think the need to
support mobile hosts across multiple, localized, LANs is
a good reason, though....

>  
>  
>  Definitions
>  ===========
>  
>  Area: One or more physical networks (subnets in the IPv4 sense),
>  interconnected by a small number of Pip routers; typically all under
>  the administration of one organization.
>  
>  Responsible Router: A Pip router which is capable of routing from one

Could this be changed to "area border router" or some such
phrase?  Have a responsible router implies that some other
router is irresponsible!  I can just see a future quote....
We use ciscos as our responsible routers and wellfleets otherwise.

>  
>  Protocol Operation (Broadcast Media)
>  ====================================
>  
>  All Systems
>  -----------
>  All systems shall periodically send a HELLO packet filled in with
>  information about itself to the all-systems-multicast address (or a

With ESIS, this is sent to all-routers.  This is preferable as it
won't bother hosts that don't care to listen to the multicasts of
other hosts.

>  
>  Hosts
>  -----
>  When a host wishes to transmit a Pip packet to an in-area host, it
>  should first search the ID table for an SNPA value.  If one is found,
>  then the host is located on the same physical wire, and the packet can
>  be sent directly.  If not, the sender should get a router list from
>  the router table, and choose the entry from that list with the
>  numerically smallest preference value that does not point to a stale
>  entry in the ID table.
>  
>  If no SNPA was found, the sender should transmit the packet

Why would a host ever have an ID entry without a corresponding
SNPA entry?  The periodically hello contains the SNPA address,
so if it is stored at all, it is stored with this address.....

If the host has no ID entry at all, then it must send to the
router because it doesn't know if the dest host is on the LAN
or not.....

Also, I think router hellos should have a bit that indicates
whether all systems that share a prefix with it are on the LAN
or not.  Thus, for the more general case of LAN-based addressing,
hosts can avoid sending hellos.....

>  
>  Responsible Routers
>  -------------------
>  A responsible router must keep track of all the systems in the area.
>  When it wishes to send a packet to a system in the area, it should
>  look up the appropriate SNPA in the table and send the packet as
>  expected.  If there is no SNPA in the table /and/ this is the only
>  Responsible Router in the area, then it may attempt to send the packet
>  as detailed for hosts.  If it does not do so, or if there is no HELLO
>  response forthcoming, then it must send back the appropriate PCMP PND
>  message as specified in [cite].

With ISIS, all routers in the area keep routing table entries for
all hosts in the area.

If only the responsible router keeps the information, how can other
routers do such things as load balancing?

>  
>  As a specific example, say that the area consists of subnet1 and
>  subnet2, which are interconnected by router1.  In addition, an exit
>  router is located on subnet1, and an inter-area router on subnet2.  It
>  is the responsibility of router1 to engage in Pip router discovery
>  with the systems on subnet1 as a proxy for the inter-area router on
>  subnet2, and with the systems on subnet2 for the exit router on
>  subnet1.

This still confuses me.  THe inter-area and exit routers will learn
about each other via the routing protocol.  Router discovery is
limited to a single subnet (LAN).

PX