Take the 2-minute tour ×
Super User is a question and answer site for computer enthusiasts and power users. It's 100% free, no registration required.

I am trying to route packets generated by a specific user out over a VPN. I have this configuration:

$ sudo iptables -S -t nat
-P PREROUTING ACCEPT
-P OUTPUT ACCEPT
-P POSTROUTING ACCEPT
-A POSTROUTING -o tun0 -j MASQUERADE 

$ sudo iptables -S -t mangle
-P PREROUTING ACCEPT
-P INPUT ACCEPT
-P FORWARD ACCEPT
-P OUTPUT ACCEPT
-P POSTROUTING ACCEPT
-A OUTPUT -m owner --uid-owner guy -j MARK --set-xmark 0xb/0xffffffff 

$ sudo ip rule show
0:      from all lookup local 
32765:  from all fwmark 0xb lookup 11 
32766:  from all lookup main 
32767:  from all lookup default 

$ sudo ip route show table 11
10.8.0.5 dev tun0  proto kernel  scope link  src 10.8.0.6 
10.8.0.6 dev tun0  scope link 
10.8.0.1 via 10.8.0.5 dev tun0 
0.0.0.0/1 via 10.8.0.5 dev tun0

$ sudo iptables -S -t raw
-P PREROUTING ACCEPT
-P OUTPUT ACCEPT
-A OUTPUT -m owner --uid-owner guy -j TRACE 
-A OUTPUT -p tcp -m tcp --dport 80 -j TRACE 

It seems that some sites work fine and use the VPN, but others don't and fall back to the normal interface. This is bad. This is a packet trace that used VPN:

Oct 27 00:24:28 agent kernel: [612979.976052] TRACE: raw:OUTPUT:rule:2 IN= OUT=eth0 SRC=XXX.YYY.ZZZ.AAA DST=23.1.17.194 LEN=60 TOS=0x00 PREC=0x00 TTL=64 ID=14494 DF PROTO=TCP SPT=57502 DPT=80 SEQ=2294732931 ACK=0 WINDOW=5840 RES=0x00 SYN URGP=0 OPT (020405B40402080A03A6E01D0000000001030307) UID=999 GID=999
Oct 27 00:24:28 agent kernel: [612979.976105] TRACE: raw:OUTPUT:policy:3 IN= OUT=eth0 SRC=XXX.YYY.ZZZ.AAA DST=23.1.17.194 LEN=60 TOS=0x00 PREC=0x00 TTL=64 ID=14494 DF PROTO=TCP SPT=57502 DPT=80 SEQ=2294732931 ACK=0 WINDOW=5840 RES=0x00 SYN URGP=0 OPT (020405B40402080A03A6E01D0000000001030307) UID=999 GID=999
Oct 27 00:24:28 agent kernel: [612979.976164] TRACE: mangle:OUTPUT:rule:1 IN= OUT=eth0 SRC=XXX.YYY.ZZZ.AAA DST=23.1.17.194 LEN=60 TOS=0x00 PREC=0x00 TTL=64 ID=14494 DF PROTO=TCP SPT=57502 DPT=80 SEQ=2294732931 ACK=0 WINDOW=5840 RES=0x00 SYN URGP=0 OPT (020405B40402080A03A6E01D0000000001030307) UID=999 GID=999
Oct 27 00:24:28 agent kernel: [612979.976210] TRACE: mangle:OUTPUT:policy:2 IN= OUT=eth0 SRC=XXX.YYY.ZZZ.AAA DST=23.1.17.194 LEN=60 TOS=0x00 PREC=0x00 TTL=64 ID=14494 DF PROTO=TCP SPT=57502 DPT=80 SEQ=2294732931 ACK=0 WINDOW=5840 RES=0x00 SYN URGP=0 OPT (020405B40402080A03A6E01D0000000001030307) UID=999 GID=999 MARK=0xb
Oct 27 00:24:28 agent kernel: [612979.976269] TRACE: nat:OUTPUT:policy:1 IN= OUT=eth0 SRC=XXX.YYY.ZZZ.AAA DST=23.1.17.194 LEN=60 TOS=0x00 PREC=0x00 TTL=64 ID=14494 DF PROTO=TCP SPT=57502 DPT=80 SEQ=2294732931 ACK=0 WINDOW=5840 RES=0x00 SYN URGP=0 OPT (020405B40402080A03A6E01D0000000001030307) UID=999 GID=999 MARK=0xb
Oct 27 00:24:28 agent kernel: [612979.976320] TRACE: filter:OUTPUT:policy:1 IN= OUT=eth0 SRC=XXX.YYY.ZZZ.AAA DST=23.1.17.194 LEN=60 TOS=0x00 PREC=0x00 TTL=64 ID=14494 DF PROTO=TCP SPT=57502 DPT=80 SEQ=2294732931 ACK=0 WINDOW=5840 RES=0x00 SYN URGP=0 OPT (020405B40402080A03A6E01D0000000001030307) UID=999 GID=999 MARK=0xb
Oct 27 00:24:28 agent kernel: [612979.976367] TRACE: mangle:POSTROUTING:policy:1 IN= OUT=tun0 SRC=XXX.YYY.ZZZ.AAA DST=23.1.17.194 LEN=60 TOS=0x00 PREC=0x00 TTL=64 ID=14494 DF PROTO=TCP SPT=57502 DPT=80 SEQ=2294732931 ACK=0 WINDOW=5840 RES=0x00 SYN URGP=0 OPT (020405B40402080A03A6E01D0000000001030307) UID=999 GID=999 MARK=0xb
Oct 27 00:24:28 agent kernel: [612979.976414] TRACE: nat:POSTROUTING:rule:1 IN= OUT=tun0 SRC=XXX.YYY.ZZZ.AAA DST=23.1.17.194 LEN=60 TOS=0x00 PREC=0x00 TTL=64 ID=14494 DF PROTO=TCP SPT=57502 DPT=80 SEQ=2294732931 ACK=0 WINDOW=5840 RES=0x00 SYN URGP=0 OPT (020405B40402080A03A6E01D0000000001030307) UID=999 GID=999 MARK=0xb

and this is one that didn't:

Oct 27 00:22:41 agent kernel: [612873.662559] TRACE: raw:OUTPUT:rule:2 IN= OUT=eth0 SRC=XXX.YYY.ZZZ.AAA DST=209.68.27.16 LEN=60 TOS=0x00 PREC=0x00 TTL=64 ID=40425 DF PROTO=TCP SPT=45305 DPT=80 SEQ=604973951 ACK=0 WINDOW=5840 RES=0x00 SYN URGP=0 OPT (020405B40402080A03A6B6960000000001030307) UID=999 GID=999
Oct 27 00:22:41 agent kernel: [612873.662609] TRACE: raw:OUTPUT:policy:3 IN= OUT=eth0 SRC=XXX.YYY.ZZZ.AAA DST=209.68.27.16 LEN=60 TOS=0x00 PREC=0x00 TTL=64 ID=40425 DF PROTO=TCP SPT=45305 DPT=80 SEQ=604973951 ACK=0 WINDOW=5840 RES=0x00 SYN URGP=0 OPT (020405B40402080A03A6B6960000000001030307) UID=999 GID=999
Oct 27 00:22:41 agent kernel: [612873.662664] TRACE: mangle:OUTPUT:rule:1 IN= OUT=eth0 SRC=XXX.YYY.ZZZ.AAA DST=209.68.27.16 LEN=60 TOS=0x00 PREC=0x00 TTL=64 ID=40425 DF PROTO=TCP SPT=45305 DPT=80 SEQ=604973951 ACK=0 WINDOW=5840 RES=0x00 SYN URGP=0 OPT (020405B40402080A03A6B6960000000001030307) UID=999 GID=999
Oct 27 00:22:41 agent kernel: [612873.662709] TRACE: mangle:OUTPUT:policy:2 IN= OUT=eth0 SRC=XXX.YYY.ZZZ.AAA DST=209.68.27.16 LEN=60 TOS=0x00 PREC=0x00 TTL=64 ID=40425 DF PROTO=TCP SPT=45305 DPT=80 SEQ=604973951 ACK=0 WINDOW=5840 RES=0x00 SYN URGP=0 OPT (020405B40402080A03A6B6960000000001030307) UID=999 GID=999 MARK=0xb
Oct 27 00:22:41 agent kernel: [612873.662761] TRACE: nat:OUTPUT:policy:1 IN= OUT=eth0 SRC=XXX.YYY.ZZZ.AAA DST=209.68.27.16 LEN=60 TOS=0x00 PREC=0x00 TTL=64 ID=40425 DF PROTO=TCP SPT=45305 DPT=80 SEQ=604973951 ACK=0 WINDOW=5840 RES=0x00 SYN URGP=0 OPT (020405B40402080A03A6B6960000000001030307) UID=999 GID=999 MARK=0xb
Oct 27 00:22:41 agent kernel: [612873.662808] TRACE: filter:OUTPUT:policy:1 IN= OUT=eth0 SRC=XXX.YYY.ZZZ.AAA DST=209.68.27.16 LEN=60 TOS=0x00 PREC=0x00 TTL=64 ID=40425 DF PROTO=TCP SPT=45305 DPT=80 SEQ=604973951 ACK=0 WINDOW=5840 RES=0x00 SYN URGP=0 OPT (020405B40402080A03A6B6960000000001030307) UID=999 GID=999 MARK=0xb
Oct 27 00:22:41 agent kernel: [612873.662855] TRACE: mangle:POSTROUTING:policy:1 IN= OUT=eth0 SRC=XXX.YYY.ZZZ.AAA DST=209.68.27.16 LEN=60 TOS=0x00 PREC=0x00 TTL=64 ID=40425 DF PROTO=TCP SPT=45305 DPT=80 SEQ=604973951 ACK=0 WINDOW=5840 RES=0x00 SYN URGP=0 OPT (020405B40402080A03A6B6960000000001030307) UID=999 GID=999 MARK=0xb

I have already tried "ip route flush cache", to no avail. I do not know why the first packet goes through the correct routing table, and the second doesn't. Both are marked.

Once again, I do not want ALL packets system-wide to go through the VPN, I only want packets from a specific user (UID=999) to go through the VPN. I am testing ipchicken.com and walmart.com via links, from the same user, same shell. walmart.com appears to use the VPN; ipchicken.com does not.

Any help appreciated. Will send 0.5 bitcoins to answerer who makes this fixed.

EDIT 2:

I have tried iptables -t raw -A OUTPUT -j NOTRACK to circumvent conntrack interference, but this hasn't worked either.

share|improve this question
add comment

1 Answer

I am fairly certain that it is an issue with your ip route table. 0.0.0.0/1 via 10.8.0.5 dev tun0 only routes IP addresses that are below 128.0.0.0. If you add the following route ip route add 128.0.0.0/1 via 10.8.0.5 table 11, it should fix the issue.

share|improve this answer
add comment

Your Answer

 
discard

By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.