On Wed, Dec 02, 2020 at 07:26:46AM +0300, Fatih USTA wrote: > > > On Tue, Dec 1, 2020 at 1:19 PM Marcin Szewczyk <marcin.szewczyk@xxxxxxxxx> wrote: > > > > Brian Aanderud on 23 Mar 2015 wrote: > > > > > What must I do to get the multicast frames routed out a 'different' > > > > > interface from the default one after applying a fwmark in iptables the > > > > > routing table? I am able to do this with unicast with a combination > > > > > of 'ip rule', 'ip route' to a different table, and iptables to apply a > > > > > 'mark'. But, the marked multicast frames never seem to follow the > > > > > other routing table's routes. > > > > > [...] > > > > I've stumbled upon the same problem as the one discussed over 5 years > > > > ago (with no answer) on this mailing list[1], ie. locally generated > > > > multicast and broadcast traffic do not seem to follow policy routing > > > > when it is constructed using `iptables --set-mark` and `ip rule fwmark`. > > > > [...] > > > > Can anyone suggest if I am trying to do something that just should not > > > > work, am I missing some small but vital detail or is it some kind of a > > > > bug? > > > > > > > > [...] > > > > [1]: https://marc.info/?l=netfilter&m=142714167809246&w=2 > > > > [2]: https://upload.wikimedia.org/wikipedia/commons/3/37/Netfilter-packet-flow.svg > By default, the multicast packet TTL 1. Have you changed the TTL? > Otherwise, the routing cannot be made because the packet's life is over. Increasing TTL doesn't seem to change anything. For broadcast it was already 64. Testing with: - nc -nvbu 255.255.255.255 2000 - nc -nvbu 255.255.255.255 3000 - nc -nvbu 239.1.1.1 2000 - nc -nvbu 239.1.1.1 3000 This works: # ip rule 0: from all lookup local 30000: from all dport 3000 lookup test 32766: from all lookup main 32767: from all lookup default This does not: # ip rule 0: from all lookup local 30000: from all fwmark 0x1 lookup test 32766: from all lookup main 32767: from all lookup default For both iptables rules are: # iptables -L OUTPUT -n -v -t mangle Chain OUTPUT (policy ACCEPT 12M packets, 1507M bytes) pkts bytes target prot opt in out source destination 4 128 TTL udp -- * * 0.0.0.0/0 0.0.0.0/0 udp dpt:3000 TTL set to 32 4 128 MARK udp -- * * 0.0.0.0/0 0.0.0.0/0 udp dpt:3000 MARK set 0x1 The test table and interfaces: # ip route show table test default dev wlp2s0.2 scope link # ip -br -4 addr | grep wlp2s0 wlp2s0 UP 192.168.1.32/24 wlp2s0.2@wlp2s0 UP 192.168.20.20/24 # ip -d link show dev wlp2s0 3: wlp2s0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc mq state UP mode DORMANT group default qlen 1000 link/ether 00:c2:c6:1d:39:e5 brd ff:ff:ff:ff:ff:ff promiscuity 0 minmtu 256 maxmtu 2304 addrgenmode none numtxqueues 4 numrxqueues 1 gso_max_size 65536 gso_max_segs 65535 # ip -d link show dev wlp2s0.2 10: wlp2s0.2@wlp2s0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue state UP mode DEFAULT group default qlen 1000 link/ether 00:c2:c6:1d:39:e5 brd ff:ff:ff:ff:ff:ff promiscuity 0 minmtu 0 maxmtu 65535 vlan protocol 802.1Q id 2 <REORDER_HDR> addrgenmode eui64 numtxqueues 1 numrxqueues 1 gso_max_size 65536 gso_max_segs 65535 tcpdump results for the working `ip rule dport` solution (dport 3000 is sent on VLAN 2): 11:59:23.301939 00:c2:c6:1d:39:e5 > ff:ff:ff:ff:ff:ff, ethertype IPv4 (0x0800), length 46: (tos 0x0, ttl 64, id 15506, offset 0, flags [DF], proto UDP (17), length 32) 192.168.1.32.37387 > 255.255.255.255.2000: UDP, length 4 0x0000: 4500 0020 3c92 4000 4011 3c73 c0a8 0120 E...<.@.@.<s.... 0x0010: ffff ffff 920b 07d0 000c ceb8 666f 6f0a ............foo. 11:59:26.485132 00:c2:c6:1d:39:e5 > ff:ff:ff:ff:ff:ff, ethertype 802.1Q (0x8100), length 50: vlan 2, p 0, ethertype IPv4, (tos 0x0, ttl 32, id 44759, offset 0, flags [DF], proto UDP (17), length 32) 192.168.20.20.51634 > 255.255.255.255.3000: UDP, length 4 0x0000: 4500 0020 aed7 4000 2011 d739 c0a8 1414 E.....@....9.... 0x0010: ffff ffff c9b2 0bb8 000c 8143 6261 720a ...........Cbar. 12:05:42.945432 00:c2:c6:1d:39:e5 > 01:00:5e:01:01:01, ethertype IPv4 (0x0800), length 46: (tos 0x0, ttl 1, id 20557, offset 0, flags [DF], proto UDP (17), length 32) 192.168.1.32.51491 > 239.1.1.1.2000: UDP, length 4 0x0000: 4500 0020 504d 4000 0111 77b5 c0a8 0120 E...PM@...w..... 0x0010: ef01 0101 c923 07d0 000c a79d 666f 6f0a .....#......foo. 12:05:56.710881 00:c2:c6:1d:39:e5 > 01:00:5e:01:01:01, ethertype 802.1Q (0x8100), length 50: vlan 2, p 0, ethertype IPv4, (tos 0x0, ttl 32, id 62586, offset 0, flags [DF], proto UDP (17), length 32) 192.168.20.20.40605 > 239.1.1.1.3000: UDP, length 4 0x0000: 4500 0020 f47a 4000 2011 a193 c0a8 1414 E....z@......... 0x0010: ef01 0101 9e9d 0bb8 000c bc55 6261 720a ...........Ubar. tcpdump results for the non-working `ip rule fwmark` solution (everything goes without VLAN tag): 11:57:54.899126 00:c2:c6:1d:39:e5 > ff:ff:ff:ff:ff:ff, ethertype IPv4 (0x0800), length 46: (tos 0x0, ttl 64, id 60815, offset 0, flags [DF], proto UDP (17), length 32) 192.168.1.32.42413 > 255.255.255.255.2000: UDP, length 4 0x0000: 4500 0020 ed8f 4000 4011 8b75 c0a8 0120 E.....@.@..u.... 0x0010: ffff ffff a5ad 07d0 000c bb16 666f 6f0a ............foo. 11:57:57.499439 00:c2:c6:1d:39:e5 > ff:ff:ff:ff:ff:ff, ethertype IPv4 (0x0800), length 46: (tos 0x0, ttl 32, id 61431, offset 0, flags [DF], proto UDP (17), length 32) 192.168.1.32.33153 > 255.255.255.255.3000: UDP, length 4 0x0000: 4500 0020 eff7 4000 2011 a90d c0a8 0120 E.....@......... 0x0010: ffff ffff 8181 0bb8 000c dc68 6261 720a ...........hbar. 12:06:35.215904 00:c2:c6:1d:39:e5 > 01:00:5e:01:01:01, ethertype IPv4 (0x0800), length 46: (tos 0x0, ttl 1, id 31632, offset 0, flags [DF], proto UDP (17), length 32) 192.168.1.32.49461 > 239.1.1.1.2000: UDP, length 4 0x0000: 4500 0020 7b90 4000 0111 4c72 c0a8 0120 E...{.@...Lr.... 0x0010: ef01 0101 c135 07d0 000c af8b 666f 6f0a .....5......foo. 12:06:39.911621 00:c2:c6:1d:39:e5 > 01:00:5e:01:01:01, ethertype IPv4 (0x0800), length 46: (tos 0x0, ttl 32, id 31890, offset 0, flags [DF], proto UDP (17), length 32) 192.168.1.32.46976 > 239.1.1.1.3000: UDP, length 4 0x0000: 4500 0020 7c92 4000 2011 2c70 c0a8 0120 E...|.@...,p.... 0x0010: ef01 0101 b780 0bb8 000c b666 6261 720a ...........fbar. -- Marcin Szewczyk http://wodny.org
