tcp - Connect socket using secondary IP address -

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not long ago, able connect given destination address either primary or secondary ip address on given interface following steps.

  1. add secondary ip address given interface using ip addr add ...,
  2. bind socket primary or secondary address, desired,
  3. connect destination ip address using primary or secondary address, bound in #2.

i upgraded machine linux 3.3.6 , no longer works, don't remember last version tried on working. know how same kind of thing in newer kernels? verified same code on 2.6.23 on different machine.

update 2 seems related nic driver. 3.3.6 , 8139too, fine. same machine, using different nic , via-rhine, problem shows up.

here's happens when run code (source @ end) on 3.3.6 (packet capture output tshark running in background):

$ ./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 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 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

and same on 2.6.23:

$ ./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 10.0.0.123 10.0.0.123 dev eth0  src 10.0.0.126     cache  mtu 1500 advmss 1460 hoplimit 64

code bind_connect:

#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; }

the problem turns out had set nat postrouting rule iptables, i.e.

chain postrouting (policy accept 11 packets, 637 bytes)  pkts bytes target     prot opt in     out     source               destination              0     0 masquerade   --     eth0.894  anywhere             anywhere

once removed rule:

$ sudo iptables -t nat -f

things started work again. had set nat rule while ago while testing problem, , forgotten remove afterward.


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