Hitchhikers Guide to the Internet | Page 6

dealing with
subnets. Frequently these machines can be used as a leaf on a network

but not as a gateway within the subnetted portion of the network. As
time passes and more systems become 4.3BSD based, these problems
should disappear.
There has been some confusion in the past over the format of an IP
broadcast address. Some machines used an address of all zeros to mean
broadcast and some all ones. This was confusing when machines of
both type were connected to the same network. The broadcast address
of all ones has been adopted to end the grief. Some systems (e.g. 4.2
BSD) allow one to choose the format of the broadcast address. If a
system does allow this choice, care should be taken that the all ones
format is chosen. (This is explained in RFC-1009 and RFC-1010).
Internet Problems
There are a number of problems with the Internet. Solutions to the
problems range from software changes to long term research projects.
Some of the major ones are detailed below:
Number of Networks
When the Internet was designed it was to have about 50 connected
networks. With the explosion of networking, the number is now
approaching 300. The software in a group of critical gateways (called
the core gateways of the ARPAnet) are not able to pass or store much
more than that number. In the short term, core reallocation and
recoding has raised the number slightly. By the summer of '88 the
current PDP-11 core gateways will be replaced with BBN Butterfly
gateways which will solve the problem.
Routing Issues
Along with sheer mass of the data necessary to route packets to a large
number of networks, there are many problems with the updating,
stability, and optimality of the routing algorithms. Much research is
being done in the area, but the optimal solution to these routing
problems is still years away. In most cases the the routing we have
today works, but sub-optimally and sometimes unpredictably.
-8-
Trust Issues
Gateways exchange network routing information. Currently, most
gateways accept on faith that the information provided about the state
of the network is correct. In the past this was not a big problem since
most of the gateways belonged to a single administrative entity

(DARPA). Now with multiple wide area networks under different
administrations, a rogue gateway somewhere in the net could cripple
the Internet. There is design work going on to solve both the problem
of a gateway doing unreasonable things and providing enough
information to reasonably route data between multiply connected
networks (multi-homed networks).
Capacity & Congestion
Many portions of the ARPAnet are very congested during the busy part
of the day. Additional links are planned to alleviate this congestion, but
the implementation will take a few months.
These problems and the future direction of the Internet are determined
by the Internet Architect (Dave Clark of MIT) being advised by the
Internet Activities Board (IAB). This board is composed of chairmen of
a number of committees with responsibility for various specialized
areas of the Internet. The committees composing the IAB and their
chairmen are:
Committee Chair Autonomous Networks Deborah Estrin End-to-End
Services Bob Braden Internet Architecture Dave Mills Internet
Engineering Phil Gross EGP2 Mike Petry Name Domain Planning
Doug Kingston Gateway Monitoring Craig Partridge Internic Jake
Feinler Performance & Congestion ControlRobert Stine NSF Routing
Chuck Hedrick Misc. MilSup Issues Mike St. Johns Privacy Steve Kent
IRINET Requirements Vint Cerf Robustness & Survivability Jim
Mathis Scientific Requirements Barry Leiner
Note that under Internet Engineering, there are a set of task forces and
chairs to look at short term concerns. The chairs of these task forces are
not part of the IAB.
-9- Routing
Routing is the algorithm by which a network directs a packet from its
source to its destination. To appreciate the problem, watch a small child
trying to find a table in a restaurant. From the adult point of view the
structure of the dining room is seen and an optimal route easily chosen.
The child, however, is presented with a set of paths between tables
where a good path, let alone the optimal one to the goal is not
discernible.***
A little more background might be appropriate. IP gateways (more
correctly routers) are boxes which have connections to multiple

networks and pass traffic between these nets. They decide how the
packet is to be sent based on the information in the IP header of the
packet and the state of the network. Each interface on a router has an
unique address appropriate to the network to which it is connected. The
information in the IP header which is used is primarily the destination
address. Other information (e.g. type of service) is largely ignored at
this time. The state of the network is determined by the routers passing
information among themselves.