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#include <stdlib.h>
#include <stdio.h>
#include <unistd.h>
#include <string.h>
#include <ctype.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <sys/time.h>
#include <errno.h>
#include <signal.h>
#include <netdb.h>
#include <netinet/in.h>
#include <netinet/in_systm.h>
#include <netinet/ip.h>
#include <netinet/ip_icmp.h>
#include <machine/in_cksum.h>
#include <alias.h>
#include "natd.h"
int SendNeedFragIcmp (int sock, struct ip* failedDgram, int mtu)
{
char icmpBuf[IP_MAXPACKET];
struct ip* ip;
struct icmp* icmp;
int icmpLen;
int failBytes;
int failHdrLen;
struct sockaddr_in addr;
int wrote;
struct in_addr swap;
/*
* Don't send error if packet is
* not the first fragment.
*/
if (ntohs (failedDgram->ip_off) & ~(IP_MF | IP_DF))
return 0;
/*
* Dont respond if failed datagram is ICMP.
*/
if (failedDgram->ip_p == IPPROTO_ICMP)
return 0;
/*
* Start building the message.
*/
ip = (struct ip*) icmpBuf;
icmp = (struct icmp*) (icmpBuf + sizeof (struct ip));
/*
* Complete ICMP part.
*/
icmp->icmp_type = ICMP_UNREACH;
icmp->icmp_code = ICMP_UNREACH_NEEDFRAG;
icmp->icmp_cksum = 0;
icmp->icmp_void = 0;
icmp->icmp_nextmtu = htons (mtu);
/*
* Copy header + 64 bits of original datagram.
*/
failHdrLen = (failedDgram->ip_hl << 2);
failBytes = failedDgram->ip_len - failHdrLen;
if (failBytes > 8)
failBytes = 8;
failBytes += failHdrLen;
icmpLen = ICMP_MINLEN + failBytes;
memcpy (&icmp->icmp_ip, failedDgram, failBytes);
/*
* Calculate checksum.
*/
icmp->icmp_cksum = InternetChecksum ((u_short*) icmp, icmpLen);
/*
* Add IP header using old IP header as template.
*/
memcpy (ip, failedDgram, sizeof (struct ip));
ip->ip_v = 4;
ip->ip_hl = 5;
ip->ip_len = htons (sizeof (struct ip) + icmpLen);
ip->ip_p = IPPROTO_ICMP;
ip->ip_tos = 0;
swap = ip->ip_dst;
ip->ip_dst = ip->ip_src;
ip->ip_src = swap;
PacketAliasIn ((char*) ip, IP_MAXPACKET);
addr.sin_family = AF_INET;
addr.sin_addr = ip->ip_dst;
addr.sin_port = 0;
/*
* Put packet into processing queue.
*/
wrote = sendto (sock,
icmp,
icmpLen,
0,
(struct sockaddr*) &addr,
sizeof addr);
if (wrote != icmpLen)
Warn ("Cannot send ICMP message.");
return 1;
}
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