src/net/net.c

/*
 *  Copyright (C) 2004-2007  Anders Gavare.  All rights reserved.
 *
 *  Redistribution and use in source and binary forms, with or without
 *  modification, are permitted provided that the following conditions are met:
 *
 *  1. Redistributions of source code must retain the above copyright
 *     notice, this list of conditions and the following disclaimer.
 *  2. Redistributions in binary form must reproduce the above copyright  
 *     notice, this list of conditions and the following disclaimer in the 
 *     documentation and/or other materials provided with the distribution.
 *  3. The name of the author may not be used to endorse or promote products
 *     derived from this software without specific prior written permission.
 *
 *  THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
 *  ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 *  IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 *  ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE   
 *  FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 *  DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 *  OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 *  HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 *  LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 *  OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 *  SUCH DAMAGE.
 *
 *
 *  $Id: net.c,v 1.12 2007/08/25 22:27:28 debug Exp $
 *
 *  Emulated network.
 *
 *  (Read the README file in this directory for more details.)
 *
 *
 *  NOTE: The 'extra' argument used in many functions in this file is a pointer
 *  to something unique for each NIC (i.e. the NIC itself :-), so that if
 *  multiple NICs are emulated concurrently, they will not get packets that
 *  are meant for some other controller.
 */

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <errno.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <netdb.h>
#include <fcntl.h>
#include <signal.h>

#include "machine.h"
#include "misc.h"
#include "net.h"


/*  #define debug fatal  */


/*
 *  net_allocate_ethernet_packet_link():
 *
 *  This routine allocates an ethernet_packet_link struct, and adds it at
 *  the end of the packet chain.  A data buffer is allocated, and the data,
 *  extra, and len fields of the link are set.
 *
 *  Note: The data buffer is not zeroed.
 *
 *  Return value is a pointer to the link on success. It doesn't return on
 *  failure.
 */
struct ethernet_packet_link *net_allocate_ethernet_packet_link(
        struct net *net, void *extra, size_t len)
{
        struct ethernet_packet_link *lp;

        CHECK_ALLOCATION(lp = malloc(sizeof(struct ethernet_packet_link)));

        lp->len = len;
        lp->extra = extra;
        CHECK_ALLOCATION(lp->data = malloc(len));

        lp->next = NULL;

        /*  Add last in the link chain:  */
        lp->prev = net->last_ethernet_packet;
        if (lp->prev != NULL)
                lp->prev->next = lp;
        else
                net->first_ethernet_packet = lp;
        net->last_ethernet_packet = lp;

        return lp;
}


/*
 *  net_arp():
 *
 *  Handle an ARP (or RARP) packet, coming from the emulated NIC.
 *
 *  An ARP packet might look like this:
 *
 *      ARP header:
 *          ARP hardware addr family:   0001
 *          ARP protocol addr family:   0800
 *          ARP addr lengths:           06 04
 *          ARP request:                0001
 *          ARP from:                   112233445566 01020304
 *          ARP to:                     000000000000 01020301
 *
 *  An ARP request with a 'to' IP value of the gateway should cause an
 *  ARP response packet to be created.
 *
 *  An ARP request with the same from and to IP addresses should be ignored.
 *  (This would be a host testing to see if there is an IP collision.)
 */
static void net_arp(struct net *net, void *extra,
        unsigned char *packet, int len, int reverse)
{
        int q;
        int i;

        /*  TODO: This debug dump assumes ethernet->IPv4 translation:  */
        if (reverse)
                debug("[ net: RARP: ");
        else
                debug("[ net: ARP: ");
        for (i=0; i<2; i++)
                debug("%02x", packet[i]);
        debug(" ");
        for (i=2; i<4; i++)
                debug("%02x", packet[i]);
        debug(" ");
        debug("%02x", packet[4]);
        debug(" ");
        debug("%02x", packet[5]);
        debug(" req=");
        debug("%02x", packet[6]);       /*  Request type  */
        debug("%02x", packet[7]);
        debug(" from=");
        for (i=8; i<18; i++)
                debug("%02x", packet[i]);
        debug(" to=");
        for (i=18; i<28; i++)
                debug("%02x", packet[i]);
        debug(" ]\n");

        if (packet[0] == 0x00 && packet[1] == 0x01 &&
            packet[2] == 0x08 && packet[3] == 0x00 &&
            packet[4] == 0x06 && packet[5] == 0x04) {
                int r = (packet[6] << 8) + packet[7];
                struct ethernet_packet_link *lp;

                switch (r) {
                case 1:         /*  Request  */
                        /*  Only create a reply if this was meant for the
                            gateway:  */
                        if (memcmp(packet+24, net->gateway_ipv4_addr, 4) != 0)
                                break;

                        lp = net_allocate_ethernet_packet_link(
                            net, extra, 60 + 14);

                        /*  Copy the old packet first:  */
                        memset(lp->data, 0, 60 + 14);
                        memcpy(lp->data + 14, packet, len);

                        /*  Add ethernet ARP header:  */
                        memcpy(lp->data + 0, lp->data + 8 + 14, 6);
                        memcpy(lp->data + 6, net->gateway_ethernet_addr, 6);
                        lp->data[12] = 0x08; lp->data[13] = 0x06;

                        /*  Address of the emulated machine:  */
                        memcpy(lp->data + 18 + 14, lp->data + 8 + 14, 10);

                        /*  Address of the gateway:  */
                        memcpy(lp->data +  8 + 14, net->gateway_ethernet_addr,
                            6);
                        memcpy(lp->data + 14 + 14, net->gateway_ipv4_addr, 4);

                        /*  This is a Reply:  */
                        lp->data[6 + 14] = 0x00; lp->data[7 + 14] = 0x02;

                        break;
                case 3:         /*  Reverse Request  */
                        lp = net_allocate_ethernet_packet_link(
                            net, extra, 60 + 14);

                        /*  Copy the old packet first:  */
                        memset(lp->data, 0, 60 + 14);
                        memcpy(lp->data + 14, packet, len);

                        /*  Add ethernet RARP header:  */
                        memcpy(lp->data + 0, packet + 8, 6);
                        memcpy(lp->data + 6, net->gateway_ethernet_addr, 6);
                        lp->data[12] = 0x80; lp->data[13] = 0x35;

                        /*  This is a RARP reply:  */
                        lp->data[6 + 14] = 0x00; lp->data[7 + 14] = 0x04;

                        /*  Address of the gateway:  */
                        memcpy(lp->data +  8 + 14, net->gateway_ethernet_addr,
                            6);
                        memcpy(lp->data + 14 + 14, net->gateway_ipv4_addr, 4);

                        /*  MAC address of emulated machine:  */
                        memcpy(lp->data + 18 + 14, packet + 8, 6);

                        /*
                         *  IP address of the emulated machine:  Automagically
                         *  generated from the MAC address. :-)
                         *
                         *  packet+8 points to the client's mac address,
                         *  for example 10:20:30:00:00:z0, where z is 0..15.
                         *  10:20:30:00:00:10 results in 10.0.0.1.
                         */
                        /*  q = (packet[8 + 3]) >> 4;  */
                        /*  q = q*15 + ((packet[8 + 4]) >> 4);  */
                        q = (packet[8 + 5]) >> 4;
                        lp->data[24 + 14] = 10;
                        lp->data[25 + 14] =  0;
                        lp->data[26 + 14] =  0;
                        lp->data[27 + 14] =  q;
                        break;
                case 2:         /*  Reply  */
                case 4:         /*  Reverse Reply  */
                default:
                        fatal("[ net: ARP: UNIMPLEMENTED request type "
                            "0x%04x ]\n", r);
                }
        } else {
                fatal("[ net: ARP: UNIMPLEMENTED arp packet type: ");
                for (i=0; i<len; i++)
                        fatal("%02x", packet[i]);
                fatal(" ]\n");
        }
}


/*
 *  net_ethernet_rx_avail():
 *
 *  Return 1 if there is a packet available for this 'extra' pointer, otherwise
 *  return 0.
 *
 *  Appart from actually checking for incoming packets from the outside world,
 *  this function basically works like net_ethernet_rx() but it only receives
 *  a return value telling us whether there is a packet or not, we don't
 *  actually get the packet.
 */
int net_ethernet_rx_avail(struct net *net, void *extra)
{
        if (net == NULL)
                return 0;

        /*
         *  If the network is distributed across multiple emulator processes,
         *  then receive incoming packets from those processes.
         */
        if (net->local_port != 0) {
                struct sockaddr_in si;
                socklen_t si_len = sizeof(si);
                int res, i, nreceived = 0;
                unsigned char buf[60000];

                do {
                        res = recvfrom(net->local_port_socket, buf,
                            sizeof(buf), 0, (struct sockaddr *)&si, &si_len);

                        if (res != -1) {
                                nreceived ++;

                                /*  fatal("[ incoming DISTRIBUTED packet, %i "
                                    "bytes from %s:%d\n", res,
                                    inet_ntoa(si.sin_addr),
                                    ntohs(si.sin_port));  */

                                /*  Add the packet to all "our" NICs on this
                                    network:  */
                                for (i=0; i<net->n_nics; i++) {
                                        struct ethernet_packet_link *lp;
                                        lp = net_allocate_ethernet_packet_link(
                                            net, net->nic_extra[i], res);
                                        memcpy(lp->data, buf, res);
                                }
                        }
                } while (res != -1 && nreceived < 100);
        }

        /*  IP protocol specific:  */
        net_udp_rx_avail(net, extra);
        net_tcp_rx_avail(net, extra);

        return net_ethernet_rx(net, extra, NULL, NULL);
}


/*
 *  net_ethernet_rx():
 *
 *  Receive an ethernet packet. (This means handing over an already prepared
 *  packet from this module to a specific ethernet controller device.)
 *
 *  Return value is 1 if there was a packet available. *packetp and *lenp
 *  will be set to the packet's data pointer and length, respectively, and
 *  the packet will be removed from the linked list). If there was no packet
 *  available, 0 is returned.
 *
 *  If packetp is NULL, then the search is aborted as soon as a packet with
 *  the correct 'extra' field is found, and a 1 is returned, but as packetp
 *  is NULL we can't return the actual packet. (This is the internal form
 *  if net_ethernet_rx_avail().)
 */
int net_ethernet_rx(struct net *net, void *extra,
        unsigned char **packetp, int *lenp)
{
        struct ethernet_packet_link *lp, *prev;

        if (net == NULL)
                return 0;

        /*  Find the first packet which has the right 'extra' field.  */

        lp = net->first_ethernet_packet;
        prev = NULL;
        while (lp != NULL) {
                if (lp->extra == extra) {
                        /*  We found a packet for this controller!  */
                        if (packetp == NULL || lenp == NULL)
                                return 1;

                        /*  Let's return it:  */
                        (*packetp) = lp->data;
                        (*lenp) = lp->len;

                        /*  Remove this link from the linked list:  */
                        if (prev == NULL)
                                net->first_ethernet_packet = lp->next;
                        else
                                prev->next = lp->next;

                        if (lp->next == NULL)
                                net->last_ethernet_packet = prev;
                        else
                                lp->next->prev = prev;

                        free(lp);

                        /*  ... and return successfully:  */
                        return 1;
                }

                prev = lp;
                lp = lp->next;
        }

        /*  No packet found. :-(  */
        return 0;
}


/*
 *  net_ethernet_tx():
 *
 *  Transmit an ethernet packet, as seen from the emulated ethernet controller.
 *  If the packet can be handled here, it will not necessarily be transmitted
 *  to the outside world.
 */
void net_ethernet_tx(struct net *net, void *extra,
        unsigned char *packet, int len)
{
        int i, eth_type, for_the_gateway;

        if (net == NULL)
                return;

        for_the_gateway = !memcmp(packet, net->gateway_ethernet_addr, 6);

        /*  Drop too small packets:  */
        if (len < 20) {
                fatal("[ net_ethernet_tx: Warning: dropping tiny packet "
                    "(%i bytes) ]\n", len);
                return;
        }

        /*
         *  Copy this packet to all other NICs on this network (except if
         *  it is aimed specifically at the gateway's ethernet address):
         */
        if (!for_the_gateway && extra != NULL && net->n_nics > 0) {
                for (i=0; i<net->n_nics; i++)
                        if (extra != net->nic_extra[i]) {
                                struct ethernet_packet_link *lp;
                                lp = net_allocate_ethernet_packet_link(net,
                                    net->nic_extra[i], len);

                                /*  Copy the entire packet:  */
                                memcpy(lp->data, packet, len);
                        }
        }

        /*
         *  If this network is distributed across multiple emulator processes,
         *  then transmit the packet to those other processes.
         */
        if (!for_the_gateway && net->remote_nets != NULL) {
                struct remote_net *rnp = net->remote_nets;
                while (rnp != NULL) {
                        send_udp(&rnp->ipv4_addr, rnp->portnr, packet, len);
                        rnp = rnp->next;
                }
        }


        /*
         *  The code below simulates the behaviour of a "NAT"-style gateway.
         *
         *  Packets that are not destined for the gateway are dropped first:
         *  (DHCP packets are let through, though.)
         */

        if (!for_the_gateway && packet[0] != 0xff && packet[0] != 0x00)
                return;

#if 0
        fatal("[ net: ethernet: ");
        for (i=0; i<6; i++)     fatal("%02x", packet[i]); fatal(" ");
        for (i=6; i<12; i++)    fatal("%02x", packet[i]); fatal(" ");
        for (i=12; i<14; i++)   fatal("%02x", packet[i]); fatal(" ");
        for (i=14; i<len; i++)  fatal("%02x", packet[i]); fatal(" ]\n");
#endif

        eth_type = (packet[12] << 8) + packet[13];

        /*  IP:  */
        if (eth_type == ETHERTYPE_IP) {
                /*  Routed via the gateway?  */
                if (for_the_gateway) {
                        net_ip(net, extra, packet, len);
                        return;
                }

                /*  Broadcast? (DHCP does this.)  */
                if (packet[0] == 0xff && packet[1] == 0xff &&
                    packet[2] == 0xff && packet[3] == 0xff &&
                    packet[4] == 0xff && packet[5] == 0xff) {
                        net_ip_broadcast(net, extra, packet, len);
                        return;
                }

                if (net->n_nics < 2) {
                        fatal("[ net_ethernet_tx: IP packet not for gateway, "
                            "and not broadcast: ");
                        for (i=0; i<14; i++)
                                fatal("%02x", packet[i]);
                        fatal(" ]\n");
                }
                return;
        }

        /*  ARP:  */
        if (eth_type == ETHERTYPE_ARP) {
                if (len != 42 && len != 60)
                        fatal("[ net_ethernet_tx: WARNING! unusual "
                            "ARP len (%i) ]\n", len);
                net_arp(net, extra, packet + 14, len - 14, 0);
                return;
        }

        /*  RARP:  */
        if (eth_type == ETHERTYPE_REVARP) {
                net_arp(net, extra, packet + 14, len - 14, 1);
                return;
        }

        /*  Sprite:  */
        if (eth_type == ETHERTYPE_SPRITE) {
                /*  TODO.  */
                fatal("[ net: TX: UNIMPLEMENTED Sprite packet ]\n");
                return;
        }

        /*  IPv6:  */
        if (eth_type == ETHERTYPE_IPV6) {
                /*  TODO.  */
                fatal("[ net_ethernet_tx: IPv6 is not implemented yet! ]\n");
                return;
        }

        fatal("[ net_ethernet_tx: ethernet packet type 0x%04x not yet "
            "implemented ]\n", eth_type);
}


/*
 *  parse_resolvconf():
 *
 *  This function parses "/etc/resolv.conf" to figure out the nameserver
 *  and domain used by the host.
 */
static void parse_resolvconf(struct net *net)
{
        FILE *f;
        char buf[8000];
        size_t len;
        int res;
        unsigned int i, start;

        /*
         *  This is a very ugly hack, which tries to figure out which
         *  nameserver the host uses by looking for the string 'nameserver'
         *  in /etc/resolv.conf.
         *
         *  This can later on be used for DHCP autoconfiguration.  (TODO)
         *
         *  TODO: This is hardcoded to use /etc/resolv.conf. Not all
         *        operating systems use that filename.
         *
         *  TODO: This is hardcoded for AF_INET (that is, IPv4).
         *
         *  TODO: This assumes that the first nameserver listed is the
         *        one to use.
         */
        f = fopen("/etc/resolv.conf", "r");
        if (f == NULL)
                return;

        /*  TODO: get rid of the hardcoded values  */
        memset(buf, 0, sizeof(buf));
        len = fread(buf, 1, sizeof(buf) - 100, f);
        fclose(f);
        buf[sizeof(buf) - 1] = '\0';

        for (i=0; i<len; i++)
                if (strncmp(buf+i, "nameserver", 10) == 0) {
                        char *p;

                        /*
                         *  "nameserver" (1 or more whitespace)
                         *  "x.y.z.w" (non-digit)
                         */

                        /*  debug("found nameserver at offset %i\n", i);  */
                        i += 10;
                        while (i<len && (buf[i]==' ' || buf[i]=='\t'))
                                i++;
                        if (i >= len)
                                break;
                        start = i;

                        p = buf+start;
                        while ((*p >= '0' && *p <= '9') || *p == '.')
                                p++;
                        *p = '\0';

#ifdef HAVE_INET_PTON
                        res = inet_pton(AF_INET, buf + start,
                            &net->nameserver_ipv4);
#else
                        res = inet_aton(buf + start, &net->nameserver_ipv4);
#endif
                        if (res < 1)
                                break;

                        net->nameserver_known = 1;
                        break;
                }

        for (i=0; i<len; i++)
                if (strncmp(buf+i, "domain", 6) == 0) {
                        /*  "domain" (1 or more whitespace) domain_name  */
                        i += 6;
                        while (i<len && (buf[i]==' ' || buf[i]=='\t'))
                                i++;
                        if (i >= len)
                                break;

                        start = i;
                        while (i<len && buf[i]!='\n' && buf[i]!='\r')
                                i++;
                        if (i < len)
                                buf[i] = '\0';
                        /*  fatal("DOMAIN='%s'\n", buf + start);  */
                        CHECK_ALLOCATION(net->domain_name = strdup(buf+start));
                        break;
                }
}


/*
 *  net_add_nic():
 *
 *  Add a NIC to a network. (All NICs on a network will see each other's
 *  packets.)
 */
void net_add_nic(struct net *net, void *extra, unsigned char *macaddr)
{
        if (net == NULL)
                return;

        if (extra == NULL) {
                fprintf(stderr, "net_add_nic(): extra = NULL\n");
                exit(1);
        }

        net->n_nics ++;
        CHECK_ALLOCATION(net->nic_extra = realloc(net->nic_extra, sizeof(void *)
            * net->n_nics));

        net->nic_extra[net->n_nics - 1] = extra;
}


/*
 *  net_gateway_init():
 *
 *  This function creates a "gateway" machine (for example at IPv4 address
 *  10.0.0.254, if the net is 10.0.0.0/8), which acts as a gateway/router/
 *  nameserver etc.
 */
static void net_gateway_init(struct net *net)
{
        unsigned char *p = (void *) &net->netmask_ipv4;
        uint32_t x;
        int xl;

        x = (p[0] << 24) + (p[1] << 16) + (p[2] << 8) + p[3];
        xl = 32 - net->netmask_ipv4_len;
        if (xl > 8)
                xl = 8;
        x |= ((1 << xl) - 1) & ~1;

        net->gateway_ipv4_addr[0] = x >> 24;
        net->gateway_ipv4_addr[1] = x >> 16;
        net->gateway_ipv4_addr[2] = x >> 8;
        net->gateway_ipv4_addr[3] = x;

        net->gateway_ethernet_addr[0] = 0x60;
        net->gateway_ethernet_addr[1] = 0x50;
        net->gateway_ethernet_addr[2] = 0x40;
        net->gateway_ethernet_addr[3] = 0x30;
        net->gateway_ethernet_addr[4] = 0x20;
        net->gateway_ethernet_addr[5] = 0x10;
}


/*
 *  net_dumpinfo():
 *
 *  Called from the debugger's "machine" command, to print some info about
 *  a network.
 */
void net_dumpinfo(struct net *net)
{
        int iadd = DEBUG_INDENTATION;
        struct remote_net *rnp;

        debug("net:\n");

        debug_indentation(iadd);

        debug("simulated network: ");
        net_debugaddr(&net->netmask_ipv4, NET_ADDR_IPV4);
        debug("/%i", net->netmask_ipv4_len);

        debug(" (max outgoing: TCP=%i, UDP=%i)\n",
            MAX_TCP_CONNECTIONS, MAX_UDP_CONNECTIONS);

        debug("simulated gateway+nameserver: ");
        net_debugaddr(&net->gateway_ipv4_addr, NET_ADDR_IPV4);
        debug(" (");
        net_debugaddr(&net->gateway_ethernet_addr, NET_ADDR_ETHERNET);
        debug(")\n");

        if (!net->nameserver_known) {
                debug("(could not determine nameserver)\n");
        } else {
                debug("simulated nameserver uses real nameserver ");
                net_debugaddr(&net->nameserver_ipv4, NET_ADDR_IPV4);
                debug("\n");
        }

        if (net->domain_name != NULL && net->domain_name[0])
                debug("domain: %s\n", net->domain_name);

        rnp = net->remote_nets;
        if (net->local_port != 0)
                debug("distributed network: local port = %i\n",
                    net->local_port);
        debug_indentation(iadd);
        while (rnp != NULL) {
                debug("remote \"%s\": ", rnp->name);
                net_debugaddr(&rnp->ipv4_addr, NET_ADDR_IPV4);
                debug(" port %i\n", rnp->portnr);
                rnp = rnp->next;
        }
        debug_indentation(-iadd);

        debug_indentation(-iadd);
}


/*
 *  net_init():
 *
 *  This function creates a network, and returns a pointer to it.
 *
 *  ipv4addr should be something like "10.0.0.0", netipv4len = 8.
 *
 *  If n_remote is more than zero, remote should be a pointer to an array
 *  of strings of the following format: "host:portnr".
 *
 *  Network settings are registered if settings_prefix is non-NULL.
 *  (The one calling net_init() is also responsible for calling net_deinit().)
 *
 *  On failure, exit() is called.
 */
struct net *net_init(struct emul *emul, int init_flags,
        const char *ipv4addr, int netipv4len,
        char **remote, int n_remote, int local_port,
        const char *settings_prefix)
{
        struct net *net;
        int res;

        CHECK_ALLOCATION(net = malloc(sizeof(struct net)));
        memset(net, 0, sizeof(struct net));

        /*  Set the back pointer:  */
        net->emul = emul;

        /*  Sane defaults:  */
        net->timestamp = 0;
        net->first_ethernet_packet = net->last_ethernet_packet = NULL;

#ifdef HAVE_INET_PTON
        res = inet_pton(AF_INET, ipv4addr, &net->netmask_ipv4);
#else
        res = inet_aton(ipv4addr, &net->netmask_ipv4);
#endif
        if (res < 1) {
                fprintf(stderr, "net_init(): could not parse IPv4 address"
                    " '%s'\n", ipv4addr);
                exit(1);
        }

        if (netipv4len < 1 || netipv4len > 30) {
                fprintf(stderr, "net_init(): extremely weird ipv4 "
                    "network length (%i)\n", netipv4len);
                exit(1);
        }
        net->netmask_ipv4_len = netipv4len;

        net->nameserver_known = 0;
        net->domain_name = "";
        parse_resolvconf(net);

        /*  Distributed network? Then add remote hosts:  */
        if (local_port != 0) {
                struct sockaddr_in si_self;

                net->local_port = local_port;
                net->local_port_socket = socket(AF_INET, SOCK_DGRAM, 0);
                if (net->local_port_socket < 0) {
                        perror("socket");
                        exit(1);
                }

                memset((char *)&si_self, 0, sizeof(si_self));
                si_self.sin_family = AF_INET;
                si_self.sin_port = htons(local_port);
                si_self.sin_addr.s_addr = htonl(INADDR_ANY);
                if (bind(net->local_port_socket, (struct sockaddr *)&si_self,
                    sizeof(si_self)) < 0) {
                        perror("bind");
                        exit(1);
                }

                /*  Set the socket to non-blocking:  */
                res = fcntl(net->local_port_socket, F_GETFL);
                fcntl(net->local_port_socket, F_SETFL, res | O_NONBLOCK);
        }
        if (n_remote != 0) {
                struct remote_net *rnp;
                while ((n_remote--) != 0) {
                        struct hostent *hp;

                        /*  debug("adding '%s'\n", remote[n_remote]);  */
                        CHECK_ALLOCATION(rnp =
                            malloc(sizeof(struct remote_net)));
                        memset(rnp, 0, sizeof(struct remote_net));

                        rnp->next = net->remote_nets;
                        net->remote_nets = rnp;

                        CHECK_ALLOCATION(rnp->name = strdup(remote[n_remote]));
                        if (strchr(rnp->name, ':') != NULL)
                                strchr(rnp->name, ':')[0] = '\0';

                        hp = gethostbyname(rnp->name);
                        if (hp == NULL) {
                                fprintf(stderr, "could not resolve '%s'\n",
                                    rnp->name);
                                exit(1);
                        }
                        memcpy(&rnp->ipv4_addr, hp->h_addr, hp->h_length);
                        free(rnp->name);

                        /*  And again:  */
                        CHECK_ALLOCATION(rnp->name = strdup(remote[n_remote]));
                        if (strchr(rnp->name, ':') == NULL) {
                                fprintf(stderr, "Remote network '%s' is not "
                                    "'host:portnr'?\n", rnp->name);
                                exit(1);
                        }
                        rnp->portnr = atoi(strchr(rnp->name, ':') + 1);
                }
        }

        if (init_flags & NET_INIT_FLAG_GATEWAY)
                net_gateway_init(net);

        net_dumpinfo(net);

        /*  This is necessary when using the real network:  */
        signal(SIGPIPE, SIG_IGN);

        return net;
}
