Path: utzoo!censor!geac!torsqnt!lethe!yunexus!ists!helios.physics.utoronto.ca!news-server.csri.toronto.edu!cs.utexas.edu!sdd.hp.com!apollo!beierl_c
From: beierl_c@apollo.HP.COM (Christopher Beierl)
Newsgroups: comp.sys.apollo
Subject: Re: internet address
Message-ID: <50115509.19050@apollo.HP.COM>
Date: 27 Feb 91 17:07:00 GMT
References: <9102261044.AA02546@apo.esiee.fr>
Reply-To: beierl_c@apollo.HP.COM (Christopher Beierl)
Organization: Hewlett-Packard Apollo Division - Chelmsford, MA
Lines: 180

In article <9102261044.AA02546@apo.esiee.fr> bonnetf@apo.esiee.fr (bonnet-franck) writes:
>Hi,
>
>Does somebody knows how to get the internet address of a machine
>when I am working on it ( whithout looking in /etc/hosts ) ?

How about

    /etc/ifconfig <interface>

where <interface> is one of dr0, dr1, eth0, etc.

    Apollo Token Ring            dr0,1
    IEEE 802.3 (ETHERNET)        eth0,1
    IEEE 802.5 (IBM Token Ring)  itr0,1
    Serial Line (SLIP)           sl0

-Chris

Here's a little program which interprets the network address info
supplied by ifconfig.  I have found it useful for explaining and
understanding network addresses, subnetting, etc.

--------------------------- Cut Here ----------------------------------
/*
** Pipe the output of "/etc/ifconfig <net>" into this program
*/

#include <stdio.h>

#define MAXLEN  256

main()
{
    int         net_shift, subnet_shift;
    char        buf[MAXLEN], *ptr, class;
    unsigned    a1, a2, a3, a4, n1, n2, n3, n4, s1, s2, s3, s4, b1, b2, b3, b4;
    unsigned    net, subnet, host, address, local_address, net_mask, subnet_mask;
    void        print_bin(), print_hex();

    fgets(buf, MAXLEN, stdin);
    printf(buf);
    if (fgets(buf, MAXLEN, stdin)) {
        printf(buf);
        for (ptr = buf; *ptr; ++ptr) {
            if (*ptr == '.') {
                *ptr = ' ';
            }
        }
        if (sscanf(buf, "%*s%u%u%u%u%*s%x%*s%u%u%u%u", &a1, &a2, &a3, &a4,
                &subnet_mask, &b1, &b2, &b3, &b4) == 9) {
            address = (a1 << 24) + (a2 << 16) + (a3 << 8) + a4;
            if ((address & 0x80000000) == 0) {
                class = 'A';
                net_mask = 0xff000000;
                net_shift = 24;
            }
            else if ((address & 0x40000000) == 0) {
                class = 'B';
                net_mask = 0xffff0000;
                net_shift = 16;
            }
            else if ((address & 0x20000000) == 0) {
                class = 'C';
                net_mask = 0xffffff00;
                net_shift = 8;
            }
            else {
                class = 'D';
                net_mask = 0xfffffff;
                net_shift = 4;
            }
            n1 = (net_mask & 0xff000000) >> 24;
            n2 = (net_mask & 0x00ff0000) >> 16;
            n3 = (net_mask & 0x0000ff00) >> 8;
            n4 = net_mask & 0x000000ff;

            s1 = (subnet_mask & 0xff000000) >> 24;
            s2 = (subnet_mask & 0x00ff0000) >> 16;
            s3 = (subnet_mask & 0x0000ff00) >> 8;
            s4 = subnet_mask & 0x000000ff;

            for (subnet_shift = 0; subnet_shift < net_shift; ++subnet_shift) {
                if (subnet_mask & (1 << subnet_shift)) {
                    break;
                }
            }

            printf("\nADDRESS\n");
            printf("(decimal) = %6u    . %6u    . %6u    . %6u\n", a1, a2, a3, a4);
            print_hex(a1, a2, a3, a4);
            print_bin(a1, a2, a3, a4);

            printf("\nBROADCAST ADDRESS\n");
            printf("(decimal) = %6u    . %6u    . %6u    . %6u\n", b1, b2, b3, b4);
            print_hex(b1, b2, b3, b4);
            print_bin(b1, b2, b3, b4);
                                               
            printf("\nNET MASK\n");
            printf("(decimal) = %6u    . %6u    . %6u    . %6u\n", n1, n2, n3, n4);
            print_hex(n1, n2, n3, n4);
            print_bin(n1, n2, n3, n4);

            printf("\nSUBNET MASK\n");
            printf("(decimal) = %6u    . %6u    . %6u    . %6u\n", s1, s2, s3, s4);
            print_hex(s1, s2, s3, s4);
            print_bin(s1, s2, s3, s4);

            net = (address & net_mask) >> net_shift;
            subnet = ((address & ~net_mask) & subnet_mask) >> subnet_shift;
            host = address & ~subnet_mask;

            printf("\nThis means:\n");
            printf("    Class:  %c\n", class);
            printf("      Net:  %d (%x hex)\n", net, net);
            printf("   Subnet:  %d (%x hex)\n", subnet, subnet);
            printf("     Host:  %d (%x hex)\n", host, host);
        }
    }
}

void
print_hex(v1, v2, v3, v4)
unsigned v1, v2, v3, v4;
{
    void p_hex();

    printf("    (hex) = ");
    p_hex(v1);
    printf("  . ");
    p_hex(v2);
    printf("  . ");
    p_hex(v3);
    printf("  . ");
    p_hex(v4);
    putchar('\n');
}

void
p_hex(d)
unsigned d;
{
    printf("%3x  %3x", (d & 0xf0) >> 4, d & 0xf);
}

void
print_bin(v1, v2, v3, v4)
unsigned v1, v2, v3, v4;
{
    void    p_bin();

    printf(" (binary) = ");
    p_bin(v1, 8);
    printf(". ");
    p_bin(v2, 8);
    printf(". ");
    p_bin(v3, 8);
    printf(". ");
    p_bin(v4, 8);
    putchar('\n');
}

void
p_bin(d, bits)
unsigned d;
int bits;
{
    for (--bits; bits >= 0; --bits) {
        putchar((d & (1 << bits)) ? '1' : '0');
        if (!(bits % 4)) {
            putchar(' ');
        }
    }
}
--------------------------- Cut Here ----------------------------------
-- 
=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
 Christopher T. Beierl  Internet: beierl_c@apollo.HP.COM;beierl_c@apollo.com
 Apollo Computer, Inc.      UUCP: {mit-eddie,yale,uw-beaver}!apollo!beierl_c
 A Subsidiary of Hewlett-Packard                       Phone: (508) 256-6600