New option --oiface for outgoing interface

.github/workflows/test.yml

@@ -44,7 +44,48 @@ jobs:
           flag-name: ${{ matrix.os }}
           parallel: true
 
+      - name: Upload fping binary
+        uses: actions/upload-artifact@v6
+        with:
+          name: fping-binary-${{ matrix.os }}-${{ github.sha }}
+          path: src/fping
+
+  Test-Asymmetric-Routing:
+    needs: [Test-Linux]
+    runs-on: ${{ matrix.os }}
+    strategy:
+      matrix:
+        os: [ubuntu-24.04]
+    steps:
+      - name: Checkout repository
+        uses: actions/checkout@v6
+
+      - name: Download fping binary from Test-Linux
+        id: download
+        uses: actions/download-artifact@v6
+        with:
+          name: fping-binary-${{ matrix.os }}-${{ github.sha }}
+          path: src/
+        continue-on-error: true
+
+      - name: Fallback - Build fping if download failed
+        if: steps.download.outcome == 'failure'
+        run: |
+          sudo apt-get update -qq
+          sudo apt-get install -y libcap2-bin libtest-command-perl
+          ci/build-1-autotools.sh
+          ci/build-4-compile.sh
+
+      - name: Make fping executable
+        run: chmod +x src/fping
+
+      - name: Install tcpdump and net-tools
+        run: |
+          sudo apt-get update -qq
+          sudo apt-get install -y tcpdump net-tools
 
+      - name: Test asymmetric routing (--oiface)
+        run: sudo ci/test-oiface.sh
 
   Test-Mac:
     runs-on: macos-latest

CHANGELOG.md

@@ -3,6 +3,8 @@ Next
 
 ## New features
 
+- New option --oiface for outgoing interface (#463, thanks @gsnw-sebast)
+
 ## Bugfixes and other changes
 
 - ci: Removed travis-ci (#446, thanks @gsnw-sebast)

ci/test-07-options-i-m.pl

@@ -1,6 +1,6 @@
 #!/usr/bin/perl -w
 
-use Test::Command tests => 25;
+use Test::Command tests => 31;
 use Test::More;
 
 #  -i n       interval between sending ping packets (in millisec) (default 25)
@@ -54,6 +54,31 @@
 $cmd->stderr_like(qr{binding to specific interface \(SO_BINDTODEVICE\):.*\n});
 }
 
+# fping --oiface=IFACE
+SKIP: {
+if($^O ne 'linux') {
+    skip '--oiface option functionality is only tested on Linux', 3;
+}
+my $cmd = Test::Command->new(cmd => 'fping --oiface=lo 127.0.0.1');
+$cmd->exit_is_num(0);
+$cmd->stdout_is_eq("127.0.0.1 is alive\n");
+$cmd->stderr_is_eq("");
+}
+
+# fping --oiface=IFACE (IPv6)
+SKIP: {
+    if($^O ne 'linux') {
+        skip '--oiface option functionality is only tested on Linux', 3;
+    }
+    if($ENV{SKIP_IPV6}) {
+        skip 'Skip IPv6 tests', 3;
+    }
+    my $cmd = Test::Command->new(cmd => 'fping -6 --oiface=lo ::1');
+    $cmd->exit_is_num(0);
+    $cmd->stdout_is_eq("::1 is alive\n");
+    $cmd->stderr_is_eq("");
+}
+
 # fping -l
 {
 my $cmd = Test::Command->new(cmd => '(sleep 0.5; pkill -INT fping)& fping -p 100 -l 127.0.0.1');

ci/test-oiface.sh

@@ -0,0 +1,79 @@
+set -ex
+
+NS_TESTER="tester_ns"
+NS_TARGET="target_ns"
+LOG_FILE="/tmp/asym_trace.log"
+
+cleanup() {
+    echo "--- FINALER TRACE-LOG ---"
+    [ -f "$LOG_FILE" ] && cat $LOG_FILE
+    sudo ip netns del $NS_TESTER 2>/dev/null || true
+    sudo ip netns del $NS_TARGET 2>/dev/null || true
+}
+trap cleanup EXIT
+
+echo "--- Network-Setup ---"
+sudo ip netns add $NS_TESTER
+sudo ip netns add $NS_TARGET
+
+sudo ip link add veth1_tst type veth peer name veth1_trg
+sudo ip link add veth2_tst type veth peer name veth2_trg
+
+sudo ip link set veth1_tst netns $NS_TESTER
+sudo ip link set veth2_tst netns $NS_TESTER
+sudo ip link set veth1_trg netns $NS_TARGET
+sudo ip link set veth2_trg netns $NS_TARGET
+
+sudo ip netns exec $NS_TESTER ip addr add 10.0.1.1/24 dev veth1_tst
+sudo ip netns exec $NS_TESTER ip addr add 10.0.2.1/24 dev veth2_tst
+sudo ip netns exec $NS_TARGET ip addr add 10.0.1.2/24 dev veth1_trg
+sudo ip netns exec $NS_TARGET ip addr add 10.0.2.2/24 dev veth2_trg
+
+sudo ip netns exec $NS_TESTER ip link set veth1_tst up
+sudo ip netns exec $NS_TESTER ip link set veth2_tst up
+sudo ip netns exec $NS_TESTER ip link set lo up
+sudo ip netns exec $NS_TARGET ip link set veth1_trg up
+sudo ip netns exec $NS_TARGET ip link set veth2_trg up
+sudo ip netns exec $NS_TARGET ip link set lo up
+
+echo "--- Configuration for asymmetric routing ---"
+for ns in $NS_TESTER $NS_TARGET; do
+    sudo ip netns exec $ns sysctl -w net.ipv4.conf.all.rp_filter=0
+    sudo ip netns exec $ns sysctl -w net.ipv4.conf.default.rp_filter=0
+    sudo ip netns exec $ns sysctl -w net.ipv4.conf.all.accept_local=1
+    sudo ip netns exec $ns sysctl -w net.ipv4.ip_forward=1
+
+    for dev in $(sudo ip netns exec $ns ls /sys/class/net/); do
+        sudo ip netns exec $ns sysctl -w net.ipv4.conf.$dev.rp_filter=0 2>/dev/null || true
+    done
+done
+
+T_MAC2=$(sudo ip netns exec $NS_TARGET cat /sys/class/net/veth2_trg/address)
+sudo ip netns exec $NS_TESTER arp -s 10.0.2.2 $T_MAC2 -i veth2_tst
+
+echo "--- Tests ---"
+sudo ip netns exec $NS_TESTER tcpdump -i any icmp -n -l > $LOG_FILE 2>&1 &
+TCP_PID=$!
+sleep 2
+
+echo "Send fping (asymmetry check)..."
+sudo ip netns exec $NS_TESTER ./src/fping -c 1 -t 1000 --oiface veth2_tst -S 10.0.1.1 10.0.2.2 || FPING_STATUS=$?
+
+sleep 1
+sudo kill $TCP_PID 2>/dev/null || true
+sleep 1
+
+echo "--- Analysis ---"
+
+REQ_OK=$(grep "veth2_tst Out IP 10.0.1.1 > 10.0.2.2" $LOG_FILE | wc -l)
+REP_OK=$(grep "veth1_tst In  IP 10.0.2.2 > 10.0.1.1" $LOG_FILE | wc -l)
+
+if [ "$REQ_OK" -gt 0 ] && [ "$REP_OK" -gt 0 ]; then
+    echo "RESULT: TEST SUCCESSFUL (True asymmetry detected)"
+    exit 0
+else
+    echo "RESULT: TEST FAILED"
+    [ "$REQ_OK" -eq 0 ] && echo "- The request was not sent correctly with source 10.0.1.1 via veth2_tst."
+    [ "$REP_OK" -eq 0 ] && echo "- The reply was not received asymmetrically via veth1_tst."
+    exit 1
+fi

doc/fping.pod

@@ -157,6 +157,10 @@ was configured with C<--enable-safe-limits>)).
 
 Set the interface (requires SO_BINDTODEVICE support).
 
+=item B<--oiface>=I<IFACE>
+
+Send pings via a specific outgoing interface (receive from any)
+
 =item B<--icmp-timestamp>
 
 Send ICMP timestamp requests (ICMP type 13) instead of ICMP Echo requests.

src/flags.c

@@ -45,6 +45,8 @@ int opt_outage_on = 0;
 int opt_random_data_on = 0;
 int opt_check_source_on = 0;
 int opt_size_on = 0;
+int opt_oiface_on = 0;
+int opt_bindiface_on = 0;
 int opt_timestamp_on = 0;
 int opt_timestamp_format = 0;
 int opt_icmp_request_typ = 0;

src/flags.h

@@ -49,6 +49,8 @@ extern int opt_outage_on;
 extern int opt_random_data_on;
 extern int opt_check_source_on;
 extern int opt_size_on;
+extern int opt_oiface_on;
+extern int opt_bindiface_on;
 extern int opt_timestamp_on;
 extern int opt_timestamp_format;
 extern int opt_icmp_request_typ;

src/fping.c

@@ -505,6 +505,7 @@ int main(int argc, char **argv)
         { "ttl", 'H', OPTPARSE_REQUIRED },
         { "interval", 'i', OPTPARSE_REQUIRED },
         { "iface", 'I', OPTPARSE_REQUIRED },
+        { "oiface", 0, OPTPARSE_REQUIRED },
         { "json", 'J', OPTPARSE_NONE },
         { "icmp-timestamp", 0, OPTPARSE_NONE },
 #ifdef SO_MARK
@@ -598,6 +599,21 @@ int main(int argc, char **argv)
 #endif
             } else if (strstr(optparse_state.optlongname, "seqmap-timeout") != NULL) {
                 opt_seqmap_timeout = strtod_strict(optparse_state.optarg) * 1000000;
+            } else if (strstr(optparse_state.optlongname, "oiface") != NULL) {
+                opt_oiface_on = 1;
+#ifdef IP_PKTINFO
+                if (socket4 >= 0) {
+                    socket_set_outgoing_iface_ipv4(socket4, optparse_state.optarg);
+                }
+#ifdef IPV6
+                if (socket6 >= 0) {
+                    socket_set_outgoing_iface_ipv6(optparse_state.optarg);
+                }
+#endif
+#else
+                fprintf(stderr, "%s: --oiface is not supported on this platform (IP_PKTINFO unavailable)\n", prog);
+                exit(3);
+#endif
             } else {
                 usage(1);
             }
@@ -848,6 +864,7 @@ int main(int argc, char **argv)
             exit(1);
 
         case 'I':
+            opt_bindiface_on = 1;
 #ifdef SO_BINDTODEVICE
             if (socket4 >= 0) {
                 if (p_setsockopt(suid, socket4, SOL_SOCKET, SO_BINDTODEVICE, optparse_state.optarg, strlen(optparse_state.optarg))) {
@@ -940,6 +957,11 @@ int main(int argc, char **argv)
         exit(1);
     }
 
+    if (opt_oiface_on && opt_bindiface_on) {
+        fprintf(stderr, "%s: specify only --oiface or -I, --iface\n", prog);
+        exit(1);
+    }
+
     if (opt_count_on && opt_loop_on) {
         fprintf(stderr, "%s: specify only one of c, l\n", prog);
         exit(1);
@@ -3075,6 +3097,9 @@ void usage(int is_error)
 #ifdef SO_BINDTODEVICE
     fprintf(out, "   -I, --iface=IFACE  bind to a particular interface\n");
 #endif
+#ifdef IP_PKTINFO
+    fprintf(out, "       --oiface=IFACE  send pings via a specific outgoing interface (receive from any)\n");
+#endif
 #ifdef SO_MARK
     fprintf(out, "   -k, --fwmark=FWMARK set the routing mark\n");
 #endif

src/fping.h

@@ -128,11 +128,13 @@ int in_cksum( unsigned short *p, int n );
 
 /* socket.c */
 int  open_ping_socket_ipv4(int *socktype);
+void socket_set_outgoing_iface_ipv4(int s, const char *iface_name);
 void init_ping_buffer_ipv4(size_t ping_data_size);
 void socket_set_src_addr_ipv4(int s, struct in_addr *src_addr, int *ident);
 int  socket_sendto_ping_ipv4(int s, struct sockaddr *saddr, socklen_t saddr_len, uint16_t icmp_seq, uint16_t icmp_id, uint8_t icmp_proto);
 #ifdef IPV6
 int  open_ping_socket_ipv6(int *socktype);
+void socket_set_outgoing_iface_ipv6(const char *iface_name);
 void init_ping_buffer_ipv6(size_t ping_data_size);
 void socket_set_src_addr_ipv6(int s, struct in6_addr *src_addr, int *ident);
 int  socket_sendto_ping_ipv6(int s, struct sockaddr *saddr, socklen_t saddr_len, uint16_t icmp_seq, uint16_t icmp_id);

src/socket4.c

@@ -40,6 +40,7 @@
 #include <netinet/in_systm.h>
 #include <netinet/ip.h>
 #include <netinet/ip_icmp.h>
+#include <net/if.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
@@ -49,6 +50,13 @@
 char* ping_buffer_ipv4 = 0;
 size_t ping_pkt_size_ipv4;
 
+/* Interface index for outgoing packets (0 = not set, use routing table) */
+static int outgoing_iface_idx_ipv4 = 0;
+
+/* Source address for outgoing packets (used to populate ipi_spec_dst) */
+static struct in_addr outgoing_src_addr_ipv4;
+static int outgoing_src_addr_set_ipv4 = 0;
+
 int open_ping_socket_ipv4(int *socktype)
 {
     struct protoent* proto;
@@ -84,6 +92,22 @@ int open_ping_socket_ipv4(int *socktype)
     return s;
 }
 
+void socket_set_outgoing_iface_ipv4(int s, const char *iface_name)
+{
+    unsigned int idx = if_nametoindex(iface_name);
+    if (idx == 0) {
+        fprintf(stderr, "fping: unknown interface '%s'\n", iface_name);
+        exit(1);
+    }
+    outgoing_iface_idx_ipv4 = (int)idx;
+
+    int on = 1;
+    if (setsockopt(s, IPPROTO_IP, IP_PKTINFO, &on, sizeof(on)) < 0) {
+        perror("setsockopt IP_PKTINFO");
+        exit(1);
+    }
+}
+
 void init_ping_buffer_ipv4(size_t ping_data_size)
 {
     /* allocate ping buffer */
@@ -98,6 +122,10 @@ void socket_set_src_addr_ipv4(int s, struct in_addr* src_addr, int *ident)
     struct sockaddr_in sa;
     socklen_t len = sizeof(sa);
 
+    /* Remember source address so we can set ipi_spec_dst in sendmsg() */
+    outgoing_src_addr_ipv4 = *src_addr;
+    outgoing_src_addr_set_ipv4 = 1;
+
     memset(&sa, 0, len);
     sa.sin_family = AF_INET;
     sa.sin_addr = *src_addr;
@@ -161,7 +189,41 @@ int socket_sendto_ping_ipv4(int s, struct sockaddr* saddr, socklen_t saddr_len,
 
     icp->icmp_cksum = calcsum((unsigned short*)icp, ping_pkt_size_ipv4);
 
-    n = sendto(s, icp, ping_pkt_size_ipv4, 0, saddr, saddr_len);
+    if (outgoing_iface_idx_ipv4 > 0) {
+        struct iovec iov = {
+            .iov_base = icp,
+            .iov_len  = ping_pkt_size_ipv4
+        };
+
+        char cmsg_buf[CMSG_SPACE(sizeof(struct in_pktinfo))];
+        memset(cmsg_buf, 0, sizeof(cmsg_buf));
+
+        struct msghdr msg = {
+            .msg_name       = saddr,
+            .msg_namelen    = saddr_len,
+            .msg_iov        = &iov,
+            .msg_iovlen     = 1,
+            .msg_control    = cmsg_buf,
+            .msg_controllen = sizeof(cmsg_buf),
+            .msg_flags      = 0
+        };
+
+        struct cmsghdr *cmsg = CMSG_FIRSTHDR(&msg);
+        cmsg->cmsg_level = IPPROTO_IP;
+        cmsg->cmsg_type  = IP_PKTINFO;
+        cmsg->cmsg_len   = CMSG_LEN(sizeof(struct in_pktinfo));
+
+        struct in_pktinfo *pktinfo = (struct in_pktinfo *)CMSG_DATA(cmsg);
+        memset(pktinfo, 0, sizeof(*pktinfo));
+        pktinfo->ipi_ifindex = outgoing_iface_idx_ipv4;
+        if (outgoing_src_addr_set_ipv4) {
+            pktinfo->ipi_spec_dst = outgoing_src_addr_ipv4;
+        }
+
+        n = sendmsg(s, &msg, 0);
+    } else {
+        n = sendto(s, icp, ping_pkt_size_ipv4, 0, saddr, saddr_len);
+    }
 
     return n;
 }