Im working with libpcap and I want to print the protocol field of the IP header and the type field of the ICMP header. Here the important code: Code: #include <pcap.h> #include <stdio.h> #include <string.h> #include <stdlib.h> #include <ctype.h> #include <errno.h> #include <sys/types.h> #include <sys/socket.h> #include <arpa/inet.h> #include <netinet/in.h> struct ip { u_int8_t ip_vhl; /* header length, version */ #define IP_V(ip) (((ip)->ip_vhl & 0xf0) >> 4) #define IP_HL(ip) ((ip)->ip_vhl & 0x0f) u_int8_t ip_tos; /* type of service */ u_int16_t ip_len; /* total length */ u_int16_t ip_id; /* identification */ u_int16_t ip_off; /* fragment offset field */ #define IP_DF 0x4000 /* dont fragment flag */ #define IP_MF 0x2000 /* more fragments flag */ #define IP_OFFMASK 0x1fff /* mask for fragmenting bits */ u_int8_t ip_ttl; /* time to live */ u_int8_t ip_p; /* protocol */ u_int16_t ip_sum; /* checksum */ struct in_addr ip_src,ip_dst; /* source and dest address */ }; struct icmp { u_int8_t icmp_type; /* type of message, see below */ u_int8_t icmp_code; /* type sub code */ u_int16_t icmp_cksum; /* ones complement cksum of struct */ }; void got_packet(u_char *args, const struct pcap_pkthdr *header, const u_char *packet) { static int count = 1; /* packet counter */ struct ip *ip; struct icmp *icmp; printf("\nPacket number %d:\n", count); count++; printf("\nProtocol field: "); switch(ip->ip_p) { case IPPROTO_IP : printf("Dummy protocol for TCP"); break; case IPPROTO_ICMP : printf("ICMP"); break; case IPPROTO_TCP : printf("TCP"); break; case IPPROTO_UDP : printf("UDP"); break; default : printf("???"); break; } fprintf(stdout," ICMP type: %d\n", icmp->icmp_type); } I call this function in my program in main() with : Code: pcap_loop(handle, num_packets, got_packet, NULL); When I start this program I do a ping to my gateway 192.168.1.1 in another window and I cant get the right values for protocol field and type field. What I need to change or to add in order to get the right values? Extra information: When I do a ping to my router I think that I should get: Protocol field: ICMP ICMP type: 0 or 8
