New option --oiface for outgoing interface and add source flag to define source ip

.github/workflows/rust-ci.yml

@@ -33,4 +33,36 @@ jobs:
         run: cargo build --all-features --verbose
 
       - name: Run tests
-        run: cargo test --all-features --verbose -- --nocapture
+        run: cargo test --all-features --verbose -- --nocapture
+
+  Test-Asymmetric-Routing:
+    needs: [ci]
+    runs-on: ${{ matrix.os }}
+
+    strategy:
+      matrix:
+        os: [ubuntu-24.04]
+
+    steps:
+      - name: Checkout repository
+        uses: actions/checkout@v5
+
+      - name: Cache cargo registry
+        uses: actions/cache@v4
+        with:
+          path: |
+            ~/.cargo/registry
+            ~/.cargo/git
+            target
+          key: ${{ runner.os }}-cargo-${{ hashFiles('**/Cargo.lock') }}
+
+      - name: Build
+        run: cargo build --all-features --verbose
+
+      - 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

CHANGELOG.md

@@ -1,3 +1,7 @@
+fping-rust 0.2.0 (new)
+======================
+- New option --oiface for outgoing interface and source ip flag (#18, @gsnw-sebast)
+
 fping-rust 0.1.1 (2026-03-28)
 ======================
 - fix: validate ICMP ID per socket, fix dual-stack ID mismatch (#15, @gsnw-sebast)

README.md

@@ -68,6 +68,7 @@ Options:
   -6, --ipv6               Use IPv6 only
       --report-all-rtts    Show all individual RTTs
   -x, --reachable <N>      Minimum number of reachable hosts to be considered success
+      --oiface <IFACE>     Bind outgoing packets to this network interface (e.g. eth0)
   -h, --help               Print help
   -V, --version            Print version
 ```

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 $NS_TESTER ./target/debug/fping -c 1 -t 1000 --oiface veth2_tst -S 10.0.1.1 10.0.2.2 || FPING_STATUS=$?
+
+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

src/args.rs

@@ -98,6 +98,14 @@ pub struct Args {
   /// Minimum number of reachable hosts to be considered success
   #[arg(short = 'x', long = "reachable", value_name = "N")]
   pub reachable: Option<u32>,
+
+  /// Source address for outgoing pings
+  #[arg(short = 'S', long = "source")]
+  pub source: Option<String>,
+
+  /// Bind outgoing packets to this network interface (e.g. eth0)
+  #[arg(long = "oiface", value_name = "IFACE")]
+  pub oiface: Option<String>,
 }
 
 impl Args {

src/pinger.rs

@@ -9,7 +9,7 @@ use crate::output::{
   print_global_stats, print_per_host_stats, print_recv, print_timeout,
   max_host_len, GlobalStatsSummary, RecvLineOpts, TimeoutLineOpts,
 };
-use crate::socket::{build_icmp_packet, open_raw_socket, recv_ping, send_ping_v4, send_ping_v6, SocketKind};
+use crate::socket::{bind_source_v4, bind_source_v6, build_icmp_packet, open_raw_socket, recv_ping, send_ping_v4, send_ping_v6, set_outgoing_iface_v4, set_outgoing_iface_v6, SocketKind};
 use crate::types::{HostEntry, PendingPing};
 
 pub fn run(args: Args, hosts_in: Vec<(String, IpAddr)>) {
@@ -56,6 +56,52 @@ pub fn run(args: Args, hosts_in: Vec<(String, IpAddr)>) {
   let fd4 = owned_fd4.as_ref().map(|o| o.as_raw_fd());
   let fd6 = owned_fd6.as_ref().map(|o| o.as_raw_fd());
 
+  if let Some(ref src) = args.source {
+    match src.parse::<IpAddr>() {
+      Ok(IpAddr::V4(_)) => {
+        if let Some(fd) = fd4 {
+          if let Err(e) = bind_source_v4(fd, src) {
+            eprintln!("fping: {}", e);
+            std::process::exit(1);
+          }
+        }
+      }
+      Ok(IpAddr::V6(_)) => {
+        if let Some(fd) = fd6 {
+          if let Err(e) = bind_source_v6(fd, src) {
+            eprintln!("fping: {}", e);
+            std::process::exit(1);
+          }
+        }
+      }
+      Err(_) => {
+        eprintln!("fping: -S/--source '{}' is not a valid IP address", src);
+        std::process::exit(1);
+      }
+    }
+  }
+
+  let oiface_idx4: Option<u32> = if let Some(ref iface) = args.oiface {
+    if let Some(fd) = fd4 {
+      match set_outgoing_iface_v4(fd, iface) {
+        Ok(idx) => Some(idx),
+        Err(e)  => { eprintln!("fping: {}", e); std::process::exit(1); }
+      }
+    } else { None }
+  } else { None };
+
+  let oiface_idx6: Option<u32> = if let Some(ref iface) = args.oiface {
+    if let Some(fd) = fd6 {
+      match set_outgoing_iface_v6(fd, iface) {
+        Ok(idx) => Some(idx),
+        Err(e)  => { eprintln!("fping: {}", e); std::process::exit(1); }
+      }
+    } else { None }
+  } else { None };
+
+  let src_v4: Option<std::net::Ipv4Addr> = args.source.as_ref().and_then(|s| s.parse::<IpAddr>().ok()).and_then(|a| if let IpAddr::V4(v4) = a { Some(v4) } else { None });
+  let src_v6: Option<std::net::Ipv6Addr> = args.source.as_ref().and_then(|s| s.parse::<IpAddr>().ok()).and_then(|a| if let IpAddr::V6(v6) = a { Some(v6) } else { None });
+
   let pid_id  = (std::process::id() & 0xFFFF) as u16;
   let my_id4  = dgram_id4.unwrap_or(pid_id);
   let my_id6  = dgram_id6.unwrap_or(pid_id);
@@ -108,8 +154,8 @@ pub fn run(args: Args, hosts_in: Vec<(String, IpAddr)>) {
       let pkt = build_icmp_packet(pkt_id, seq, args.size, is_ipv6, kind);
 
       let sent = match hosts[idx].addr {
-        IpAddr::V4(ref a) => fd4.map(|fd| send_ping_v4(fd, a, &pkt)).unwrap_or(false),
-        IpAddr::V6(ref a) => fd6.map(|fd| send_ping_v6(fd, a, &pkt)).unwrap_or(false),
+        IpAddr::V4(ref a) => fd4.map(|fd| send_ping_v4(fd, a, &pkt, oiface_idx4, src_v4)).unwrap_or(false),
+        IpAddr::V6(ref a) => fd6.map(|fd| send_ping_v6(fd, a, &pkt, oiface_idx6, src_v6)).unwrap_or(false),
       };
 
       if sent && !seqmap.contains_key(&seq) {