After doing a route add <host> 127.0.0.1 -blackhole on a FreeBSD 8.3 host I noticed that nc <host> 80 would instantly return with ENETUNRACH, instead of timing out, while blackhole routing to a real host would time out. Checking in CURRENT (october 2012) reveals the same behaviour: # netstat -nr Routing tables Internet: Destination Gateway Flags Refs Use Netif Expire default 10.0.2.2 UGS 0 1 vtnet0 10.0.2.0/24 link#1 U 0 1295 vtnet0 10.0.2.15 link#1 UHS 0 0 lo0 10.0.3.0/24 link#2 U 0 0 vtnet1 10.0.3.4 link#2 UHS 0 0 lo0 127.0.0.1 link#3 UH 0 1479 lo0 Internet6: Destination Gateway Flags Netif Expire ::/96 ::1 UGRS lo0 ::1 link#3 UH lo0 ::ffff:0.0.0.0/96 ::1 UGRS lo0 fe80::/10 ::1 UGRS lo0 fe80::%vtnet1/64 link#2 U vtnet1 fe80::a00:27ff:fea4:1a9a%vtnet1 link#2 UHS lo0 fe80::%lo0/64 link#3 U lo0 fe80::1%lo0 link#3 UHS lo0 ff01::%vtnet1/32 fe80::a00:27ff:fea4:1a9a%vtnet1 U vtnet1 ff01::%lo0/32 ::1 U lo0 ff02::/16 ::1 UGRS lo0 ff02::%vtnet1/32 fe80::a00:27ff:fea4:1a9a%vtnet1 U vtnet1 ff02::%lo0/32 ::1 U lo0 # route add 4.2.2.1 127.0.0.1 -blackhole add host 4.2.2.1: gateway 127.0.0.1 # route add 4.2.2.2 10.0.2.15 -blackhole add host 4.2.2.2: gateway 10.0.2.15 # time nc -v -w 3 4.2.2.2 80 nc: connect to 4.2.2.2 port 80 (tcp) failed: Operation timed out real 0m3.089s user 0m0.000s sys 0m0.014s # time nc -v -w 3 4.2.2.1 80 nc: connect to 4.2.2.1 port 80 (tcp) failed: Network is unreachable real 0m0.014s user 0m0.000s sys 0m0.014s # uname -a FreeBSD citske.localdomain 10.0-CURRENT FreeBSD 10.0-CURRENT #3 r241988M: Wed Oct 24 15:21:27 CEST 2012 root_at_citske.localdomain:/usr/obj/usr/src/sys/CITSKE i386 A quick grep -r through the kernel did not provide me with any obvious mistake, but a colleague suggested that for localhost an if 'statement' like the following might be missing somewhere: if (rt && rt->rt_flags & (RTF_REJECT|RTF_BLACKHOLE)) { m_freem(m); return (rt->rt_flags & RTF_BLACKHOLE ? 0 : rt->rt_flags & RTF_HOST ? EHOSTUNREACH : ENETUNREACH); } Any pointers would be appreciated Nick Hibma nick_at_van-laarhoven.org GTD: Time management for chaotic people.Received on Tue Apr 23 2013 - 17:13:40 UTC
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