Temporary IPv6 Addresses

Temporary IPv6 addresses were introduced for privacy reasons in RFC 3041 and updated in RFC 4941. A good overview is given by Privacy and IPv6 Addresses . Another discussion at Understanding security flaws in IPv6 addressing schemes is also relevant.

Listing all IP addresses on a host

The function getifaddrs() will list all IP addresses on the interfaces of the host it is run on. The man page gives a program #define _GNU_SOURCE /* To get defns of NI_MAXSERV and NI_MAXHOST */ #include <arpa/inet.h> #include <sys/socket.h> #include <netdb.h> #include <ifaddrs.h> #include <stdio.h> #include <stdlib.h> #include <unistd.h> #include <linux/if_link.h> int main(int argc, char *argv[]) { struct ifaddrs *ifaddr, *ifa; int family, s, n; char host[NI_MAXHOST]; if (getifaddrs(&ifaddr) == -1) { perror("getifaddrs"); exit(EXIT_FAILURE); } /* Walk through linked list, maintaining head pointer so we can free list later */ for (ifa = ifaddr, n = 0; ifa != NULL; ifa = ifa->ifa_next, n++) { if (ifa->ifa_addr == NULL) continue; family = ifa->ifa_addr->sa_family; /* Display interface name and family (including symbolic form of the latter for the common families) */ printf("%-8s %s (%d)\n", ifa->ifa_name, (family == AF_PACKET) ? "AF_PACKET" : (family == AF_INET) ? "AF_INET" : (family == AF_INET6) ? "AF_INET6" : "???", family); /* For an AF_INET* interface address, display the address */ if (family == AF_INET || family == AF_INET6) { s = getnameinfo(ifa->ifa_addr, (family == AF_INET) ? sizeof(struct sockaddr_in) : sizeof(struct sockaddr_in6), host, NI_MAXHOST, NULL, 0, NI_NUMERICHOST); if (s != 0) { printf("getnameinfo() failed: %s\n", gai_strerror(s)); exit(EXIT_FAILURE); } printf("\t\taddress: <%s>\n", host); } else if (family == AF_PACKET && ifa->ifa_data != NULL) { struct rtnl_link_stats *stats = ifa->ifa_data; printf("\t\ttx_packets = %10u; rx_packets = %10u\n" "\t\ttx_bytes = %10u; rx_bytes = %10u\n", stats->tx_packets, stats->rx_packets, stats->tx_bytes, stats->rx_bytes); } } freeifaddrs(ifaddr); exit(EXIT_SUCCESS); }

On one of my hosts, running it gives

lo       AF_PACKET (17)
		tx_packets =      34146; rx_packets =      34146
		tx_bytes   =    4521698; rx_bytes   =    4521698
enp3s0   AF_PACKET (17)
		tx_packets =          0; rx_packets =          0
		tx_bytes   =          0; rx_bytes   =          0
wlp2s0   AF_PACKET (17)
		tx_packets =    2521087; rx_packets =    4530609
		tx_bytes   =  577960812; rx_bytes   = 1254696604
lo       AF_INET (2)
		address: <127.0.0.1>
wlp2s0   AF_INET (2)
		address: <10.0.237.126>
lo       AF_INET6 (10)
		address: <::1>
wlp2s0   AF_INET6 (10)
		address: <2400:3740:200:d900:1d55:c3c7:4d47:4d02>
wlp2s0   AF_INET6 (10)
		address: <2400:3740:200:d900:90c8:cd68:244:2bac>
wlp2s0   AF_INET6 (10)
		address: <2400:3740:200:d900:6070:9918:bafd:51a5>
wlp2s0   AF_INET6 (10)
		address: <2400:3740:200:d900:3c58:d451:fae2:5a81>
wlp2s0   AF_INET6 (10)
		address: <2400:3740:200:d900:387a:a68c:7a40:6503>
wlp2s0   AF_INET6 (10)
		address: <fe80::f7c3:950c:6f91:90e6%wlp2s0>
      

Using a temporary address to connect to a service

An API is discussed in RFC 5014 IPv6 Socket API for Source Address Selection and implemented in Linux.

There are many web sites which will tell you the IP address you have connected from. Many of them are quite verbose. Dennis points to checkip.dyndns.com as giving one-line answers, with a simple script to extract an IPv4 address at Simplest way to check for dynamic IP change :

wget -q -O - checkip.dyndns.com | grep -Po "[\d\.]+"	  
      

Code from https://gist.github.com/jirihnidek/388271b57003c043d322

An alternative 'global' method is described in IPv6 privacy extensions on Linux using entries in /proc/sys/net/ipv6/conf/eth0/use_tempaddr. Hide code

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