From c160c6b035ac86d53860631269d0f614b5f209a9 Mon Sep 17 00:00:00 2001 From: Gunnar Beutner Date: Fri, 7 May 2021 18:55:42 +0200 Subject: [PATCH] Kernel: Use correct destination MAC address for multicast packets Previously we'd incorrectly use the default gateway's MAC address. Instead we must use destination MAC addresses that are derived from the multicast IPv4 address. With this patch applied I can query mDNS on a real network. --- Kernel/Net/Routing.cpp | 8 ++++++++ 1 file changed, 8 insertions(+) diff --git a/Kernel/Net/Routing.cpp b/Kernel/Net/Routing.cpp index 28e44057dd..e207cd35f4 100644 --- a/Kernel/Net/Routing.cpp +++ b/Kernel/Net/Routing.cpp @@ -122,6 +122,11 @@ bool RoutingDecision::is_zero() const return adapter.is_null() || next_hop.is_zero(); } +static MACAddress multicast_ethernet_address(IPv4Address const& address) +{ + return MACAddress { 0x01, 0x00, 0x5e, (u8)(address[1] & 0x7f), address[2], address[3] }; +} + RoutingDecision route_to(const IPv4Address& target, const IPv4Address& source, const RefPtr through) { auto matches = [&](auto& adapter) { @@ -198,6 +203,9 @@ RoutingDecision route_to(const IPv4Address& target, const IPv4Address& source, c if (target_addr == 0xffffffff && matches(adapter)) return { adapter, { 0xff, 0xff, 0xff, 0xff, 0xff, 0xff } }; + if ((target_addr & IPv4Address { 240, 0, 0, 0 }.to_u32()) == IPv4Address { 224, 0, 0, 0 }.to_u32()) + return { adapter, multicast_ethernet_address(target) }; + { Locker locker(arp_table().lock()); auto addr = arp_table().resource().get(next_hop_ip);