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fix: use correct guest IP for slirp4netns port forwarding #216

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fix: use correct guest IP for slirp4netns port forwarding #216

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14 changes: 7 additions & 7 deletions src/network/slirp.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -175,10 +175,10 @@ impl SlirpNetwork {
set -e

# Create slirp0 TAP for slirp4netns connectivity
# Use 10.0.2.100 as the address for DNAT to work with port forwarding
# Use 10.0.2.15 as the guest address (standard slirp4netns guest IP)
# fd00::100 for IPv6 (slirp4netns uses fd00::/64 subnet with gateway fd00::2)
ip tuntap add {slirp_dev} mode tap
ip addr add 10.0.2.100/24 dev {slirp_dev}
ip addr add 10.0.2.15/24 dev {slirp_dev}
ip -6 addr add fd00::100/64 dev {slirp_dev}
ip link set {slirp_dev} up

Expand Down Expand Up @@ -227,9 +227,9 @@ iptables -t nat -A POSTROUTING -s {guest_subnet} -o {slirp_dev} -j MASQUERADE 2>
ip6tables -t nat -A POSTROUTING -s {guest_ipv6_subnet} -o {slirp_dev} -j MASQUERADE 2>/dev/null || true

# Set up DNAT for inbound connections from slirp4netns
# When slirp4netns forwards traffic to 10.0.2.100, redirect it to the actual guest IP
# This enables port forwarding: host -> slirp4netns -> 10.0.2.100 -> DNAT -> guest (192.168.x.2)
iptables -t nat -A PREROUTING -d 10.0.2.100 -j DNAT --to-destination {guest_ip} 2>/dev/null || true
# When slirp4netns forwards traffic to 10.0.2.15, redirect it to the actual guest IP
# This enables port forwarding: host -> slirp4netns -> 10.0.2.15 -> DNAT -> guest (192.168.x.2)
iptables -t nat -A PREROUTING -d 10.0.2.15 -j DNAT --to-destination {guest_ip} 2>/dev/null || true
"#,
slirp_dev = self.slirp_device,
fc_tap = self.tap_device,
Expand Down Expand Up @@ -388,15 +388,15 @@ iptables -t nat -A PREROUTING -d 10.0.2.100 -j DNAT --to-destination {guest_ip}
super::Protocol::Udp => "udp",
};

// Port forward to slirp's internal guest IP (10.0.2.100)
// Port forward to slirp's internal guest IP (10.0.2.15)
// which then gets routed to the actual guest via IP forwarding
let request = serde_json::json!({
"execute": "add_hostfwd",
"arguments": {
"proto": proto,
"host_addr": bind_addr,
"host_port": mapping.host_port,
"guest_addr": "10.0.2.100",
"guest_addr": "10.0.2.15",
"guest_port": mapping.guest_port
}
});
Expand Down
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