Paul Francis (Tsuchiya) -- 19 May 1992
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Pip: The `P' Internet Protocol

Paul F. Tsuchiya
Bellcore
tsuchiya@thumper.bellcore.com
May 19, 1992

1.0  Purpose of this draft

Pip is an IP protocol that scales, encodes policy, and is high speed. The 
purpose of this draft is to explain the basic concepts behind Pip so that 
people can start thinking about potential pitfalls. I am proposing Pip as an 
alternative to the two "medium term" proposals that emerged from the 
Road (Routing and Addressing) group to deal with the dual IP problems 
of scaling and address depletion. Because this proposal, which represents 
new ideas, is competing with old (and therefore well thought-out) ideas, I 
wish to circulate it (and get the process started) as quickly as possible, 
albeit in not as complete a form as I would like. I expect to have a 
complete proposal by the beginning of September. There will be a plenary 
presentation and a BOF covering this material at the Boston meeting of 
IETF.

2.0  Pip General

Pip has the following features:

1.      Pip carries multiple address types in a common format. As such, it is 
beneficial for transition from one address to another, and for future 
evolution (of routing techniques as well as of addressing schemes).

2.      The Pip address is completely general (multiple levels of hierarchy, 
expands to any number of systems).

3.      The Pip address is compact-it grows with the number of systems.

4.      The Pip address efficiently encodes policy (source-based) routes, both 
in "long form" (explicit path) and "short form" (path identifier).

5.      Because the Pip address can be a path identifier (multi-layer if de-
sired, like the ATM VCI/VPI), Pip can be used in a connection-orient-
ed fashion (this paper only briefly touches on mechanisms for 
controlling connections).

6.      The Pip address includes multicasting (potentially substantially more 
sophisticated than what is for IP multicast numbers, for instance, hier-
archical multicast).

7.      Pip efficiently encodes QOS (Quality-of-Service) information.

8.      The routing table lookup with Pip is well-bounded (by the depth of 
the address hierarchy).

9.      Pip accommodates "multiple defaults" routing from (multi-homed) 
stub domains.

10.     Pip allows intra-domain routing and hosts to operate with no notion 
of the "inter-domain" parts of their address, if desired. This is equiva-
lent to current IP hosts and intra-domain routers not needing to know 
their own network number.

11.     Pip accommodates tunneling across transit domains.

12.     By virtue of 8 and 9, Pip accommodates separation of interior and ex-
terior routing.

13.     Pip simplifies handling mobile systems (by having flat network layer 
identifiers).

In short, Pip is a "next generation" protocol, intended to allow the internet 
to evolve over the foreseeable future.

One of the design philosophies behind Pip is that it encodes all "routing" 
information (what is traditionally spread over the address and QOS fields) 
in a single structure (the Routing Directive). The rules for parsing the 
structure are simple on one hand, but provide a rich set of routing 
functions. Therefore, it is possible to build a single forwarding engine that 
will accommodate many different types of routing styles, including 
traditional hierarchical addresses, policy, source route, and virtual circuit. 
This way, the forwarding engine can be built in hardware and can remain 
constant even while internet routing evolves.

Another design philosophy behind Pip is that it delays the definition of 
how internet packet should be composed and interpreted. The meaning of 
addresses and QOS information are dynamically determined by 
information in Directory Services, distributed protocols such as routing 
protocols, and MIBs, rather than in a protocol specification. Current 
internet protocols have continuously been moving towards this 
philosophy, but with header formats that are not conducive to late 
semantic definition. Pip facilitates late semantic definition of the internet 
protocol header. This on one hand makes it easier to evolve the internet 
incrementally, but requires that all systems (hosts, routers, and directory 
servers) be a little smarter, and that algorithms be a little more complex. 
This, in a nutshell, is the trade-off being made by Pip.