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Aft r Sept. I, regist r on-sit bytaking this form to the generalpublic registration d k at thSan Diego Convention Cent r.Registration is open Sundaythrough Thursday.

by the Internet Engineering Ta k Forceand the Internet Architecture Board.Even if CIDR is adopted though, IP willhave to move to a wider space sooner orlater, and how to do so is the subject ofheated debate.

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assignment of blocks of Class C addressesto a rvice provider, which then allocatesthem to an organization, a single prefix forthe service pro' r can be announced in­stead of lots of individual numbers.

CIDR is currently Wlder consideration

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The most crucial issue in the Internet today twork nwnbers instead of a sin-is routing and addre ing. The combina . 8 address. Just giving lots of Classof not enough addresses and C addresses would ccmpound the rootingrouting tables are threatening to . table problems, so inter-d<xnain routing pro-the network. Here's a party ver- tocoIs would be modified to use variable-sion of the i ues inv eel. length network addresses. With inteDigent

The Internet PI: sa 32-bit r-'-------------------...-----------------------addre field, room for 4.2 billion address-es. You can't u aD potential addressesthough, or you don't have much of a net-

ork. Routing protocol are used by arouter to "armounce" to other routerswhich hosts can be. reached. If each nodegets a unique addres given out at random,like with Ethernet addresses, each hosthas to be individually announced and, in theworst case, routershave to schlepparound 4.2 billionroute announcements.

To avoid the prob­lem of unmanageablerouting tables, the IPaddress is split into anetwork nwnberhost nwnber.of tellingabout available hosts,routers announce which networks th yknow about.

The trick is to balance the split be­tween the network and host number . Ifthe network number uses a lot of bits,then you can have lot of networks, buteach 0 can ha e a' hosts. ForIP, the etwork Information Center as­signs three classes, or types, of networkaddresses, Class A networks support 16million hosts, but the larg ho t pacemeans that there are only 126 a.V3lI:·able

Class A networks, of which 46 have al­ready been assigned.

Class 8 networks support 65,534 ho ts.Because the network addre i larger,there are 16,256 po ible Cia 8 net­works. Cia C networks support only 255hosts, but there are several million avail­able Class C network nwnbers.

Here's the problem. Most networks are,or plan to be, bigger than 255 oodes. Every­body wants the flexblity of a Class 8 ad­dress, but there are 5,400 already a ignedand the figure is doubling every year,

Simple math shows that we will, givencurrent trends, run out of Class 8 spacesometime in 1993. Moreover, routing ta­bles are g tting huge, with more than5,000 networks announced on the ationalScience Foundation' SF et baCJlbOIlle

A proposed solution is known asles Inter-Domain Routing (CIDR), Orga­nizations would be allocated a block of

CARL MALAMUD is writing Exploringthe Internet: A Technical Travelogue, abook that will be featured as T1te lnteropBook at lnterop Fall. Tile opinions ex­pressed are his own,

CheckR servtce No. 15

. July 20, 1992 Communications W