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POConnect socket using secondary IP address
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copied!<p>Not too long ago, I was able to connect to a given destination address from either a primary or secondary IP address on a given interface the following steps.</p> <ol> <li>add a secondary IP address to a given interface using <code>ip addr add ...</code>,</li> <li>bind a socket to the primary or secondary address, as desired,</li> <li>connect to destination ip address using primary or secondary address, as bound in #2.</li> </ol> <p>I recently upgraded a machine to Linux 3.3.6 and this no longer works, but I don't remember the last version I tried it on that was actually working. Does anyone know how to do the same kind of thing in newer kernels? I just verified the same code on 2.6.23 on a different machine.</p> <blockquote> <p><strong>UPDATE 2</strong> This seems to be related to the NIC driver. With 3.3.6 and <strong>8139too</strong>, everything is fine. Same machine, but using a different NIC and <strong>via-rhine</strong>, then the problem shows up.</p> </blockquote> <p>Here's what happens when I run the code (source at end) on 3.3.6 (packet capture output from <code>tshark</code> running in the background):</p> <pre><code>$ ./bind_connect 10.0.1.124 10.0.1.120 Bound socket: 10.0.1.120 [10.0.1.120->10.0.1.124] # wrong source IP (should use 10.0.1.120 from bind) # | # v $ 121.051052 10.0.1.220 -> 10.0.1.124 50418 80 TCP 74 50418 > 80 [SYN] Seq=3358582895 Win=14600 Len=0 MSS=1460 SACK_PERM=1 TSval=30589624 TSecr=0 WS=128 121.051428 10.0.1.124 -> 10.0.1.220 80 50418 TCP 74 80 > 50418 [SYN, ACK] Seq=1815118993 Ack=3358582896 Win=5792 Len=0 MSS=1460 SACK_PERM=1 TSval=8157158 TSecr=30589624 WS=2 121.051475 10.0.1.220 -> 10.0.1.124 50418 80 TCP 66 50418 > 80 [ACK] Seq=3358582896 Ack=1815118994 Win=14720 Len=0 TSval=30589624 TSecr=8157158 121.051504 10.0.1.220 -> 10.0.1.124 50418 80 TCP 66 50418 > 80 [FIN, ACK] Seq=3358582896 Ack=1815118994 Win=14720 Len=0 TSval=30589624 TSecr=8157158 121.051768 10.0.1.124 -> 10.0.1.220 80 50418 TCP 66 80 > 50418 [ACK] Seq=1815118994 Ack=3358582897 Win=5792 Len=0 TSval=8157158 TSecr=30589624 121.051913 10.0.1.124 -> 10.0.1.220 80 50418 TCP 66 80 > 50418 [FIN, ACK] Seq=1815118994 Ack=3358582897 Win=5792 Len=0 TSval=8157158 TSecr=30589624 121.051941 10.0.1.220 -> 10.0.1.124 50418 80 TCP 66 50418 > 80 [ACK] Seq=3358582897 Ack=1815118995 Win=14720 Len=0 TSval=30589625 TSecr=8157158 $ ./bind_connect 10.0.1.124 10.0.1.220 Bound socket: 10.0.1.220 [10.0.1.220->10.0.1.124] $ 124.139966 10.0.1.220 -> 10.0.1.124 41470 80 TCP 74 41470 > 80 [SYN] Seq=1404133303 Win=14600 Len=0 MSS=1460 SACK_PERM=1 TSval=30590551 TSecr=0 WS=128 124.140421 10.0.1.124 -> 10.0.1.220 80 41470 TCP 74 80 > 41470 [SYN, ACK] Seq=1918490481 Ack=1404133304 Win=5792 Len=0 MSS=1460 SACK_PERM=1 TSval=8157467 TSecr=30590551 WS=2 124.140478 10.0.1.220 -> 10.0.1.124 41470 80 TCP 66 41470 > 80 [ACK] Seq=1404133304 Ack=1918490482 Win=14720 Len=0 TSval=30590551 TSecr=8157467 124.140553 10.0.1.220 -> 10.0.1.124 41470 80 TCP 66 41470 > 80 [FIN, ACK] Seq=1404133304 Ack=1918490482 Win=14720 Len=0 TSval=30590551 TSecr=8157467 124.140934 10.0.1.124 -> 10.0.1.220 80 41470 TCP 66 80 > 41470 [ACK] Seq=1918490482 Ack=1404133305 Win=5792 Len=0 TSval=8157467 TSecr=30590551 124.140976 10.0.1.124 -> 10.0.1.220 80 41470 TCP 66 80 > 41470 [FIN, ACK] Seq=1918490482 Ack=1404133305 Win=5792 Len=0 TSval=8157467 TSecr=30590551 124.140995 10.0.1.220 -> 10.0.1.124 41470 80 TCP 66 41470 > 80 [ACK] Seq=1404133305 Ack=1918490483 Win=14720 Len=0 TSval=30590551 TSecr=8157467 $ uname -a Linux erebus.mn.ca 3.3.6-1-ARCH #1 SMP PREEMPT Sun May 13 09:59:18 UTC 2012 i686 GNU/Linux $ ip route get 10.0.1.124 10.0.1.124 dev eth0.894 src 10.0.1.220 cache ipid 0x61ca rtt 3ms rttvar 3ms cwnd 10 </code></pre> <p>And then the same on 2.6.23:</p> <pre><code>$ ./bind_connect 10.0.0.123 10.0.0.226 > Bound socket: 10.0.0.226 [10.0.0.226->10.0.0.123] $ 231.566278 10.0.0.226 -> 10.0.0.123 TCP 54109 > http [SYN] Seq=0 Win=5840 Len=0 MSS=1460 TSV=99922052 TSER=0 WS=5 231.566448 10.0.0.123 -> 10.0.0.226 TCP http > 54109 [SYN, ACK] Seq=0 Ack=1 Win=5792 Len=0 MSS=1460 TSV=7060755 TSER=99922052 WS=1 231.566463 10.0.0.226 -> 10.0.0.123 TCP 54109 > http [ACK] Seq=1 Ack=1 Win=5856 Len=0 TSV=99922052 TSER=7060755 231.566510 10.0.0.226 -> 10.0.0.123 TCP 54109 > http [FIN, ACK] Seq=1 Ack=1 Win=5856 Len=0 TSV=99922052 TSER=7060755 231.566593 10.0.0.123 -> 10.0.0.226 TCP http > 54109 [ACK] Seq=1 Ack=2 Win=5792 Len=0 TSV=7060755 TSER=99922052 231.566704 10.0.0.123 -> 10.0.0.226 TCP http > 54109 [FIN, ACK] Seq=1 Ack=2 Win=5792 Len=0 TSV=7060755 TSER=99922052 231.566737 10.0.0.226 -> 10.0.0.123 TCP 54109 > http [ACK] Seq=2 Ack=2 Win=5856 Len=0 TSV=99922052 TSER=7060755 $ ./bind_connect 10.0.0.123 10.0.0.126 > Bound socket: 10.0.0.126 [10.0.0.126->10.0.0.123] $ 235.824867 10.0.0.126 -> 10.0.0.123 TCP 34228 > http [SYN] Seq=0 Win=5840 Len=0 MSS=1460 TSV=99926310 TSER=0 WS=5 235.825185 10.0.0.123 -> 10.0.0.126 TCP http > 34228 [SYN, ACK] Seq=0 Ack=1 Win=5792 Len=0 MSS=1460 TSV=7061180 TSER=99926310 WS=1 235.825236 10.0.0.126 -> 10.0.0.123 TCP 34228 > http [ACK] Seq=1 Ack=1 Win=5856 Len=0 TSV=99926311 TSER=7061180 235.825273 10.0.0.126 -> 10.0.0.123 TCP 34228 > http [FIN, ACK] Seq=1 Ack=1 Win=5856 Len=0 TSV=99926311 TSER=7061180 235.825721 10.0.0.123 -> 10.0.0.126 TCP http > 34228 [ACK] Seq=1 Ack=2 Win=5792 Len=0 TSV=7061180 TSER=99926311 235.825722 10.0.0.123 -> 10.0.0.126 TCP http > 34228 [FIN, ACK] Seq=1 Ack=2 Win=5792 Len=0 TSV=7061180 TSER=99926311 235.825756 10.0.0.126 -> 10.0.0.123 TCP 34228 > http [ACK] Seq=2 Ack=2 Win=5856 Len=0 TSV=99926311 TSER=7061180 $ uname -a Linux gaia.mn.ca 2.6.23.17-88.fc7 #1 SMP Thu May 15 00:35:10 EDT 2008 i686 i686 i386 GNU/Linux $ ip route get 10.0.0.123 10.0.0.123 dev eth0 src 10.0.0.126 cache mtu 1500 advmss 1460 hoplimit 64 </code></pre> <p>Code for bind_connect:</p> <pre><code>#include <arpa/inet.h> #include <errno.h> #include <netinet/in.h> #include <netinet/tcp.h> #include <stdio.h> #include <sys/socket.h> #include <sys/types.h> #include <unistd.h> int main(int argc, char **argv) { struct sockaddr_in sn; socklen_t sn_len; struct sockaddr_in src; struct sockaddr_in dst; int sock; char b1[INET_ADDRSTRLEN]; char b2[INET_ADDRSTRLEN]; char b3[INET_ADDRSTRLEN]; src.sin_family = dst.sin_family = AF_INET; src.sin_port = 0; dst.sin_port = htons(80); if (argc < 3) { printf("missing argument\n"); return 1; } if (inet_pton(AF_INET, argv[1], &dst.sin_addr) != 1) { perror("pton"); return -errno; } if (inet_pton(AF_INET, argv[2], &src.sin_addr) != 1) { perror("pton"); return -errno; } sock = socket(AF_INET, SOCK_STREAM, 0); if (sock < 0) { perror("socket"); return -errno; } if (bind(sock, (struct sockaddr*)&src, sizeof src) != 0) { perror("bind"); return -errno; } sn_len = sizeof sn; if (getsockname(sock, (struct sockaddr*)&sn, &sn_len) != 0) { perror("getsockname"); return -errno; } printf("Bound socket: %s [%s->%s]\n", inet_ntop(AF_INET, &sn.sin_addr, b1, sizeof b1), inet_ntop(AF_INET, &src.sin_addr, b2, sizeof b2), inet_ntop(AF_INET, &dst.sin_addr, b3, sizeof b3)); if (connect(sock, (struct sockaddr*)&dst, sizeof dst) != 0) { perror("connect"); return -errno; } close(sock); return 0; } </code></pre>

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