1. Chapter 17 routing sockets

2. abstract Introduction datalink socket address structure reading and writing sysctl operation get_ifi_info function interface name and index fuction

3. Introduction Access the Unix routing table within the kernel –ioctl command (SIOCADDRT, SIODELRT) –netstat: read the kernel memory to obtain the contents of the routing table Routing daemons (gated) –monitor ICMP –AF_ROUTE domain => cleaned up the interface to the kernel’s routing system –only type of socket supported in the route domain => raw socket

4. Three type of operation on routing socket –process can send a message to the kernel by writing to a routing socket(addition and deletion of routes, Only superuser) –process can read a message from the kernel on a routing socket (Only superuser) –process can use the sysctl function to either dump the routing table or to list all the configured interface

5. datalink socket address structure Returned by routing socket Structure sockaddr_dl{ uint8_t sdl_len; sa_family_t sdl_family; /*AF_LINK*/ uint16_t sdl_index;/*system assigned index*/ uint8_t sdl_type; /*IFT_ETHER*/ uint8_t sdl_nlen; /*name length*/ uint8_t sdl_alen;/*link-layer address length*/ uint8_t sdl_slen;/* link-layer selector length */ char sdl_data[12];/*minimum work area, name and link-layer address*/ };

6. reading and writing After a process create a routing socket, it can send commands to the kernel by writing to the socket and read information from the kernel by reading from the socket Three different structure are exchanged across a routing socket –rt_msghdr, if_msghdr, ifa_msghdr (figure 17-3)

7. Figure 17-2

8. Data exchanged with kernel across routing socket for RTM_GET command

9. Figure 17-6 #include"unproute.h" #defineBUFLEN(sizeof(struct rt_msghdr) + 512) /* 8 * sizeof(struct sockaddr_in6) = 192 */ #defineSEQ9999 int main(int argc, char **argv) { int sockfd; char*buf; pid_tpid; ssize_tn; struct rt_msghdr *rtm; struct sockaddr*sa, *rti_info[RTAX_MAX]; struct sockaddr_in*sin;

10. Figure 17-6(2) if (argc != 2)err_quit("usage: getrt "); sockfd = Socket(AF_ROUTE, SOCK_RAW, 0);/* need superuser privileges */ buf = Calloc(1, BUFLEN);/* and initialized to 0 */ rtm = (struct rt_msghdr *) buf; rtm->rtm_msglen = sizeof(struct rt_msghdr) + sizeof(struct sockaddr_in); rtm->rtm_version = RTM_VERSION; rtm->rtm_type = RTM_GET; rtm->rtm_addrs = RTA_DST; rtm->rtm_pid = pid = getpid(); rtm->rtm_seq = SEQ; sin = (struct sockaddr_in *) (rtm + 1); sin->sin_family = AF_INET; Inet_pton(AF_INET, argv[1], &sin->sin_addr); Write(sockfd, rtm, rtm->rtm_msglen); do { n = Read(sockfd, rtm, BUFLEN); } while (rtm->rtm_type != RTM_GET || rtm->rtm_seq != SEQ || rtm->rtm_pid != pid);

11. Figure 17-6(2) rtm = (struct rt_msghdr *) buf; sa = (struct sockaddr *) (rtm + 1); get_rtaddrs(rtm->rtm_addrs, sa, rti_info); if ( (sa = rti_info[RTAX_DST]) != NULL) printf("dest: %s\n", Sock_ntop_host(sa, sa->sa_len)); if ( (sa = rti_info[RTAX_GATEWAY]) != NULL) printf("gateway: %s\n", Sock_ntop_host(sa, sa->sa_len)); if ( (sa = rti_info[RTAX_NETMASK]) != NULL) printf("netmask: %s\n", Sock_masktop(sa, sa->sa_len)); if ( (sa = rti_info[RTAX_GENMASK]) != NULL) printf("genmask: %s\n", Sock_masktop(sa, sa->sa_len)); exit(0); }

12. rti_info structure filled in by our get_rtaddrs function

13. Figure 17-9 #include"unproute.h" #define ROUNDUP(a, size) (((a) & ((size)-1)) ? (1 + ((a) | ((size)-1))) : (a)) /* Step to next socket address structure; if sa_len is 0, assume it is sizeof(u_long). */ #define NEXT_SA(ap)ap = (struct sockaddr *) \ ((caddr_t) ap + (ap->sa_len ? ROUNDUP(ap->sa_len, sizeof (u_long)) : \ sizeof(u_long))) void get_rtaddrs(int addrs, struct sockaddr *sa, struct sockaddr **rti_info) { inti; for (i = 0; i < RTAX_MAX; i++) { if (addrs & (1 << i)) { rti_info[i] = sa; NEXT_SA(sa); } else rti_info[i] = NULL; }

14. sysctl operation Any process can examine both the routing table and the interface list. #include int sysctl(int *name, u_int namelen, void *oldp, size_t *oldlenp, void *newp, size_t newlen); returns:0 if OK, -1 on error

15. Hierarchical arrangement of sysctl names

16. Sysctl information returned for route domain

17. One per interface: interface name, index, and hardware address One per address: configured for the interface Information returned for sysctl,CTL_NET,NET_RT_IFLIST command

18. Figure 17-14 #include"unproute.h" #include #include /* for UDPCTL_xxx constants */ int main(int argc, char **argv) { intmib[5], val; size_t len; mib[0] = CTL_NET; mib[1] = AF_INET; mib[2] = IPPROTO_UDP; mib[3] = UDPCTL_CHECKSUM; len = sizeof(val); Sysctl(mib, 4, &val, &len, NULL, 0); printf("udp checksum flag: %d\n", val); exit(0); }

19. interface name and index fuction RFC 2133 defines four function that deal with interface names and indexes ==>these are used with IPv6 multicasting(chapter 19) each interface has a unique name and a unique positive index(0 is never used )

20. #include unsigned int if_nametoindex(const char *ifname); returns:positive interface index if OK, 0 on error char *if_indextoname(unsigned int ifindex, char *ifname); returns:pointer to interface name if OK, NULL on error struct if_nameindex *if_nameindex(void); returns:nonnull pointer if OK, NULL on error void if_freenameindex(struct if_nameindex *ptr);

21. if_nameindex return a pointer to an array of if_nameindex structure Struct if_nameindex{ unsigned int if_index;/*1, 2,…...*/ char *if_name;/*null terminated name*/ }