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lurscher
Asked: 2011-05-22 10:43:26 +0800 CST

opvnvpn: addressing nodes in LAN-behinds

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I've setup an openvpn server which i can access remotely, once it is connected, it creates a tun0 device on both server and client with virtual ip 10.15.119.x. the openvpn server is itself 10.15.119.1.

Question: how do i address other nodes in the lan behind the openvpn server? i can access services on the openvpn server itself with the address 10.15.119.1:(port), but i don't know how to address other nodes not partaking in the openvpn connection that are in the same LAN as the openvpn server: I would hope that such nodes can be addressed from the client node with some other virtual ip in the 10.15.119.x range, and if that is the case, i would only need a way to know what those ip are

i very well could create some iptables and route commands to forward ports to other specific nodes, but i'm sure there has to be a nicer way to do it, addressing directly the nodes

server.conf:

dev tun
server 10.15.119.0 255.255.255.0
ifconfig-pool-persist ipp.txt
push "route 192.168.0.0 255.255.255.0"
up ./office.up 
tls-server
dh /home/lurscher/keys/dh1024.pem
ca /home/lurscher/keys/ca.crt
cert /home/lurscher/keys/vpnCh8TestServer.crt
key /home/lurscher/keys/vpnCh8TestServer.key
status openvpn-status.log
log         openvpn.log
comp-lzo
verb 3

the office.up script has:

#!/bin/sh
#route 10.15.119.0 255.255.255.0
route add -net 10.15.119.0 netmask 255.255.255.0 gw $5 #fixed the wrong 10.15.0.0 address

client.conf instead has:

dev tun
remote my.server.com
tls-client
pull 
ca /home/chuckq/keys/ca.crt
cert /home/chuckq/keys/vpnCh8TestClient.crt
key /home/chuckq/keys/vpnCh8TestClient.key
ns-cert-type server
; port 1194
; user nobody
; group nogroup
status openvpn-status.log
log         openvpn.log
comp-lzo
verb 3

New relevant logs from server:

Thu May 26 16:59:59 2011 vpnCh8TestClient/Y.Y.Y.Y:1194 PUSH: Received control message: 'PUSH_REQUEST'
Thu May 26 16:59:59 2011 vpnCh8TestClient/Y.Y.Y.Y:1194 SENT CONTROL [vpnCh8TestClient]: 'PUSH_REPLY,route 192.168.0.0 255.255.255.0,route 10.15.119.1,topology net30,ifconfig 10.15.119.6 10.15.119.5' (status=1)
Thu May 26 17:02:17 2011 vpnCh8TestClient/Y.Y.Y.Y:1194 Replay-window backtrack occurred [1]

relevant logs from client:

Thu May 26 16:53:30 2011 [vpnCh8TestServer] Peer Connection Initiated with [AF_INET]X.X.X.X:1194
Thu May 26 16:53:32 2011 SENT CONTROL [vpnCh8TestServer]: 'PUSH_REQUEST' (status=1)
Thu May 26 16:53:32 2011 PUSH: Received control message: 'PUSH_REPLY,route 192.168.0.0 255.255.255.0,route 10.15.119.1,topology net30,ifconfig 10.15.119.6 10.15.119.5'
Thu May 26 16:53:32 2011 OPTIONS IMPORT: --ifconfig/up options modified
Thu May 26 16:53:32 2011 OPTIONS IMPORT: route options modified
Thu May 26 16:53:32 2011 ROUTE default_gateway=10.21.2.254
Thu May 26 16:53:32 2011 TUN/TAP device tun0 opened
Thu May 26 16:53:32 2011 TUN/TAP TX queue length set to 100
Thu May 26 16:53:32 2011 /sbin/ifconfig tun0 10.15.119.6 pointopoint 10.15.119.5 mtu 1500
Thu May 26 16:53:32 2011 /sbin/route add -net 192.168.0.0 netmask 255.255.255.0 gw 10.15.119.5
Thu May 26 16:53:32 2011 /sbin/route add -net 10.15.119.1 netmask 255.255.255.255 gw 10.15.119.5
Thu May 26 16:53:32 2011 Initialization Sequence Completed

EDIT thanks to wolfgangsz which noticed a typo in the office.up, i tried again tracepath with no improvements:

$ tracepath 192.168.0.100
 1:  10.15.119.6                                              0.261ms pmtu 1500
 1:  10.15.119.1                                             88.989ms 
 1:  10.15.119.1                                             58.752ms 
 2:  no reply

note how different is the result when the ip is the one from the openvpn server

$ tracepath 192.168.0.101
 1:  10.15.119.6                                              0.308ms pmtu 1500
 1:  192.168.0.101                                       115.713ms reached
 1:  192.168.0.101                                        65.064ms reached
     Resume: pmtu 1500 hops 1 back 64

routing entries at the client:

$ route -n
Kernel IP routing table
Destination     Gateway         Genmask         Flags Metric Ref    Use Iface
10.15.119.5     0.0.0.0         255.255.255.255 UH    0      0        0 tun0
10.15.119.1     10.15.119.5     255.255.255.255 UGH   0      0        0 tun0
192.168.0.0     10.15.119.5     255.255.255.0   UG    0      0        0 tun0
10.21.2.0       0.0.0.0         255.255.255.0   U     1      0        0 eth0
169.254.0.0     0.0.0.0         255.255.0.0     U     1000   0        0 eth0
0.0.0.0         10.21.2.254     0.0.0.0         UG    0      0        0 eth0

and routing entries at the (openvpn) server:

$ route -n
Kernel IP routing table
Destination     Gateway         Genmask         Flags Metric Ref    Use Iface
10.15.119.2     0.0.0.0         255.255.255.255 UH    0      0        0 tun0
10.15.119.0     10.15.119.2     255.255.255.0   UG    0      0        0 tun0
192.168.0.0     0.0.0.0         255.255.255.0   U     0      0        0 eth1
169.254.0.0     0.0.0.0         255.255.0.0     U     0      0        0 eth0
169.254.0.0     0.0.0.0         255.255.0.0     U     0      0        0 vboxnet0
0.0.0.0         192.168.0.1     0.0.0.0         UG    0      0        0 eth1
0.0.0.0         0.0.0.0         0.0.0.0         U     1002   0        0 eth0
0.0.0.0         0.0.0.0         0.0.0.0         U     1004   0        0 vboxnet0

EDIT 2: i've checked that ip forwarding is enabled

$ cat /proc/sys/net/ipv4/ip_forward
1

here is the output of the iptables in the server:

$ sudo iptables -nv -L
Chain INPUT (policy DROP 1 packets, 52 bytes)
 pkts bytes target     prot opt in     out     source               destination         
    0     0 DROP       all  --  eth0   *       127.0.0.1            0.0.0.0/0           
    0     0 DROP       all  --  eth0   *       0.0.0.0/0            127.0.0.1           
    0     0 DROP       all  --  eth0   *       192.168.0.0/16       0.0.0.0/0           
    0     0 DROP       all  --  eth0   *       172.16.0.0/12        0.0.0.0/0           
    0     0 DROP       all  --  eth0   *       10.0.0.0/8           0.0.0.0/0           
    8   416 ACCEPT     all  --  *      *       127.0.0.1            0.0.0.0/0           
    0     0 ACCEPT     all  --  *      *       0.0.0.0/0            127.0.0.1           
    0     0 ACCEPT     icmp --  *      *       0.0.0.0/0            0.0.0.0/0           icmp type 8 
    0     0 ACCEPT     tcp  --  *      *       0.0.0.0/0            0.0.0.0/0           tcp dpt:80 
   91  8915 ACCEPT     tcp  --  *      *       0.0.0.0/0            0.0.0.0/0           tcp dpt:22 
  293 28499 ACCEPT     udp  --  *      *       0.0.0.0/0            0.0.0.0/0           udp dpt:1194 
    1  1500 ACCEPT     all  --  tun+   *       0.0.0.0/0            0.0.0.0/0           
    0     0 ACCEPT     all  --  tap+   *       0.0.0.0/0            0.0.0.0/0           
   18  2010 ACCEPT     all  --  eth1   *       0.0.0.0/0            0.0.0.0/0           
    0     0 ACCEPT     all  --  *      *       0.0.0.0/0            0.0.0.0/0           state RELATED,ESTABLISHED 

Chain FORWARD (policy DROP 0 packets, 0 bytes)
 pkts bytes target     prot opt in     out     source               destination         
    0     0 DROP       all  --  eth0   *       127.0.0.1            0.0.0.0/0           
    0     0 DROP       all  --  eth0   *       0.0.0.0/0            127.0.0.1           
    0     0 DROP       all  --  eth0   *       192.168.0.0/16       0.0.0.0/0           
    0     0 DROP       all  --  eth0   *       172.16.0.0/12        0.0.0.0/0           
    0     0 DROP       all  --  eth0   *       10.0.0.0/8           0.0.0.0/0           
    0     0 DROP       tcp  --  *      eth0    0.0.0.0/0            0.0.0.0/0           tcp spts:137:139 
    0     0 DROP       udp  --  *      eth0    0.0.0.0/0            0.0.0.0/0           udp spts:137:139 
    0     0 DROP       all  --  eth1   *      !10.0.0.0/24          0.0.0.0/0           
   38 57000 ACCEPT     all  --  tun+   *       0.0.0.0/0            0.0.0.0/0           
    0     0 ACCEPT     all  --  tap+   *       0.0.0.0/0            0.0.0.0/0           
    0     0 ACCEPT     all  --  eth1   *       0.0.0.0/0            0.0.0.0/0           
    0     0 ACCEPT     all  --  *      eth0    0.0.0.0/0            0.0.0.0/0           state NEW 
    0     0 ACCEPT     all  --  *      *       0.0.0.0/0            0.0.0.0/0           state RELATED,ESTABLISHED 

Chain OUTPUT (policy ACCEPT 306 packets, 34543 bytes)
 pkts bytes target     prot opt in     out     source               destination         
    0     0 DROP       tcp  --  *      eth0    0.0.0.0/0            0.0.0.0/0           tcp spts:137:139 
    0     0 DROP       udp  --  *      eth0    0.0.0.0/0            0.0.0.0/0           udp spts:137:139 
    0     0 ACCEPT     all  --  *      eth0    0.0.0.0/0            0.0.0.0/0           state NEW

EDIT 3

i think i've left an important piece of information out, i didn't thought it might be relevant, but a recent answer made me tought it might; the openvpn is directly connected to the router, and in the router configuration (at 192.168.0.1) i've enabled port forwarding for openvpn port 1194 to the openvpn server, this is how i'm currently connecting remotely

EDIT 4

I've tried to run the following on the 192.168.0.100 (secondary server) machine, in order to see if i can solve this by giving it a route to the 10.15.119.x route:

sudo route add -net 10.15.119.0 netmask 255.255.255.0 gw 192.168.0.101

(the 192.168.0.101 is the openvpn server address, 192.168.0.100 is the secondary server i want to reach from outside)

i tried this and ping 10.15.119.1 works to reach out to the openvpn server, but ping 10.15.119.6 (my client ip) just fails

EDIT 5

i've added the results of tcpdump on the openvpn server when trying to ping 192.168.0.100 from the client:

$ sudo tcpdump -v -i any host 192.168.0.100
tcpdump: listening on any, link-type LINUX_SLL (Linux cooked), capture size 65535 bytes
11:10:43.675915 IP (tos 0x0, ttl 64, id 0, offset 0, flags [DF], proto ICMP (1), length 84)
    10.15.119.6 > services-host-1.local: ICMP echo request, id 2494, seq 1, length 64
11:10:43.675932 IP (tos 0x0, ttl 63, id 0, offset 0, flags [DF], proto ICMP (1), length 84)
    10.15.119.6 > services-host-1.local: ICMP echo request, id 2494, seq 1, length 64
11:10:43.676149 IP (tos 0x0, ttl 64, id 40127, offset 0, flags [none], proto ICMP (1), length 84)
    services-host-1.local > 10.15.119.6: ICMP echo reply, id 2494, seq 1, length 64
11:10:43.778583 IP (tos 0x0, ttl 255, id 0, offset 0, flags [DF], proto UDP (17), length 103)
    services-host-1.local.mdns > 224.0.0.251.mdns: 0*- [0q] 1/0/0 100.0.168.192.in-addr.arpa. (Cache flush) PTR services-host-1.local. (75)
11:10:43.778588 IP (tos 0x0, ttl 255, id 0, offset 0, flags [DF], proto UDP (17), length 103)
    services-host-1.local.mdns > 224.0.0.251.mdns: 0*- [0q] 1/0/0 100.0.168.192.in-addr.arpa. (Cache flush) PTR services-host-1.local. (75)
11:10:44.681801 IP (tos 0x0, ttl 64, id 0, offset 0, flags [DF], proto ICMP (1), length 84)
    10.15.119.6 > services-host-1.local: ICMP echo request, id 2494, seq 2, length 64
11:10:44.681809 IP (tos 0x0, ttl 63, id 0, offset 0, flags [DF], proto ICMP (1), length 84)
    10.15.119.6 > services-host-1.local: ICMP echo request, id 2494, seq 2, length 64
11:10:44.682007 IP (tos 0x0, ttl 64, id 40128, offset 0, flags [none], proto ICMP (1), length 84)
    services-host-1.local > 10.15.119.6: ICMP echo reply, id 2494, seq 2, length 64
11:10:45.689926 IP (tos 0x0, ttl 64, id 0, offset 0, flags [DF], proto ICMP (1), length 84)
    10.15.119.6 > services-host-1.local: ICMP echo request, id 2494, seq 3, length 64
11:10:45.689933 IP (tos 0x0, ttl 63, id 0, offset 0, flags [DF], proto ICMP (1), length 84)
    10.15.119.6 > services-host-1.local: ICMP echo request, id 2494, seq 3, length 64
11:10:45.690121 IP (tos 0x0, ttl 64, id 40129, offset 0, flags [none], proto ICMP (1), length 84)
    services-host-1.local > 10.15.119.6: ICMP echo reply, id 2494, seq 3, length 64
11:10:46.698990 IP (tos 0x0, ttl 64, id 0, offset 0, flags [DF], proto ICMP (1), length 84)
    10.15.119.6 > services-host-1.local: ICMP echo request, id 2494, seq 4, length 64
11:10:46.698997 IP (tos 0x0, ttl 63, id 0, offset 0, flags [DF], proto ICMP (1), length 84)
    10.15.119.6 > services-host-1.local: ICMP echo request, id 2494, seq 4, length 64
11:10:46.699190 IP (tos 0x0, ttl 64, id 40130, offset 0, flags [none], proto ICMP (1), length 84)
    services-host-1.local > 10.15.119.6: ICMP echo reply, id 2494, seq 4, length 64
11:10:47.706870 IP (tos 0x0, ttl 64, id 0, offset 0, flags [DF], proto ICMP (1), length 84)
    10.15.119.6 > services-host-1.local: ICMP echo request, id 2494, seq 5, length 64
11:10:47.706878 IP (tos 0x0, ttl 63, id 0, offset 0, flags [DF], proto ICMP (1), length 84)
    10.15.119.6 > services-host-1.local: ICMP echo request, id 2494, seq 5, length 64
11:10:47.707067 IP (tos 0x0, ttl 64, id 40131, offset 0, flags [none], proto ICMP (1), length 84)
    services-host-1.local > 10.15.119.6: ICMP echo reply, id 2494, seq 5, length 64
11:10:48.680540 ARP, Ethernet (len 6), IPv4 (len 4), Request who-has services-host-1.local tell openvpnServer, length 28
11:10:48.680737 ARP, Ethernet (len 6), IPv4 (len 4), Reply services-host-1.local is-at 08:00:27:a4:e2:01 (oui Unknown), length 28
11:10:48.684812 ARP, Ethernet (len 6), IPv4 (len 4), Request who-has dfdlinkrouter tell services-host-1.local, length 28
11:10:48.685338 ARP, Ethernet (len 6), IPv4 (len 4), Reply dfdlinkrouter is-at 00:26:5a:ae:90:88 (oui Unknown), length 46
11:10:48.716100 IP (tos 0x0, ttl 64, id 0, offset 0, flags [DF], proto ICMP (1), length 84)
    10.15.119.6 > services-host-1.local: ICMP echo request, id 2494, seq 6, length 64
11:10:48.716107 IP (tos 0x0, ttl 63, id 0, offset 0, flags [DF], proto ICMP (1), length 84)
    10.15.119.6 > services-host-1.local: ICMP echo request, id 2494, seq 6, length 64
11:10:48.716347 IP (tos 0x0, ttl 64, id 40132, offset 0, flags [none], proto ICMP (1), length 84)
    services-host-1.local > 10.15.119.6: ICMP echo reply, id 2494, seq 6, length 64

so it seems the ping are reaching the server and he replies back, but the packets are dropped before going into the vpn, so i added a line in iptables to log all INPUT and FORWARD packets dropped or rejected and here are what is being filtered in /var/log/syslog

May 30 10:59:24 openvpnServer kernel: [40433.898392] iptables INPUT denied: IN=eth1 OUT= MAC= SRC=192.168.0.101 DST=224.0.0.251 LEN=98 TOS=0x00 PREC=0x00 TTL=255 ID=0 DF PROTO=UDP SPT=5353 DPT=5353 LEN=78 
May 30 10:59:24 openvpnServer kernel: [40434.001003] iptables INPUT denied: IN=eth1 OUT= MAC=01:00:5e:00:00:fb:08:00:27:a4:e2:01:08:00 SRC=192.168.0.100 DST=224.0.0.251 LEN=62 TOS=0x00 PREC=0x00 TTL=255 ID=0 DF PROTO=UDP SPT=5353 DPT=5353 LEN=42 
May 30 10:59:24 openvpnServer kernel: [40434.001102] iptables INPUT denied: IN=eth1 OUT= MAC= SRC=192.168.0.101 DST=224.0.0.251 LEN=72 TOS=0x00 PREC=0x00 TTL=255 ID=0 DF PROTO=UDP SPT=5353 DPT=5353 LEN=52 
May 30 11:03:28 openvpnServer kernel: [40677.329586] iptables INPUT denied: IN=eth1 OUT= MAC= SRC=192.168.0.101 DST=224.0.0.251 LEN=67 TOS=0x00 PREC=0x00 TTL=255 ID=0 DF PROTO=UDP SPT=5353 DPT=5353 LEN=47 
May 30 11:03:29 openvpnServer kernel: [40678.330065] iptables INPUT denied: IN=eth1 OUT= MAC= SRC=192.168.0.101 DST=224.0.0.251 LEN=67 TOS=0x00 PREC=0x00 TTL=255 ID=0 DF PROTO=UDP SPT=5353 DPT=5353 LEN=47

i've commented out most DROP and REJECT commands from iptables to see if that works, but i'm still getting the same problem, here is my iptables after removing all the drops

$ sudo iptables -L -nv
Chain INPUT (policy ACCEPT 88 packets, 15209 bytes)
 pkts bytes target     prot opt in     out     source               destination         
 3404 3162K ACCEPT     all  --  lo     *       0.0.0.0/0            0.0.0.0/0           
    0     0 REJECT     all  --  !lo    *       0.0.0.0/0            127.0.0.0/8         reject-with icmp-port-unreachable 
 2950  249K ACCEPT     all  --  tun+   *       0.0.0.0/0            0.0.0.0/0           
12881 6906K ACCEPT     all  --  *      *       0.0.0.0/0            0.0.0.0/0           state RELATED,ESTABLISHED 
  162  9696 ACCEPT     tcp  --  *      *       0.0.0.0/0            0.0.0.0/0           state NEW tcp dpt:22 
    1    42 ACCEPT     udp  --  *      *       0.0.0.0/0            0.0.0.0/0           udp dpt:1194 
    0     0 ACCEPT     icmp --  *      *       0.0.0.0/0            0.0.0.0/0           icmp type 8 
   60 10407 LOG        all  --  *      *       0.0.0.0/0            0.0.0.0/0           limit: avg 5/min burst 5 LOG flags 0 level 7 prefix `iptables INPUT denied: ' 

Chain FORWARD (policy ACCEPT 0 packets, 0 bytes)
 pkts bytes target     prot opt in     out     source               destination         
   30  2448 ACCEPT     all  --  tun+   *       0.0.0.0/0            0.0.0.0/0           
    0     0 ACCEPT     all  --  *      *       0.0.0.0/0            0.0.0.0/0           state RELATED,ESTABLISHED 
    0     0 ACCEPT     udp  --  *      *       0.0.0.0/0            0.0.0.0/0           udp dpt:1194 
    0     0 LOG        all  --  *      *       0.0.0.0/0            0.0.0.0/0           limit: avg 5/min burst 5 LOG flags 0 level 7 prefix `iptables FORWARD denied: ' 

Chain OUTPUT (policy ACCEPT 0 packets, 0 bytes)
 pkts bytes target     prot opt in     out     source               destination         
 2826  857K ACCEPT     all  --  *      tun+    0.0.0.0/0            0.0.0.0/0           
17443 5842K ACCEPT     all  --  *      *       0.0.0.0/0            0.0.0.0/0

EDIT 6

as suggested by Steven, i've added 3 tcpdumps, 2 at the server and one at the client, while from the client, running

$ ping 192.168.0.100
PING 192.168.0.100 (192.168.0.100) 56(84) bytes of data.
^C
--- 192.168.0.100 ping statistics ---
5 packets transmitted, 0 received, 100% packet loss, time 4024ms

but first i flushed al iptables rules at the openvpn server:

$ sudo iptables -L -nv
Chain INPUT (policy ACCEPT 206 packets, 26537 bytes)
 pkts bytes target     prot opt in     out     source               destination         

Chain FORWARD (policy ACCEPT 0 packets, 0 bytes)
 pkts bytes target     prot opt in     out     source               destination         

Chain OUTPUT (policy ACCEPT 50 packets, 7781 bytes)
 pkts bytes target     prot opt in     out     source               destination

here is the output of the first tcpdump at the openvpn server

$ sudo tcpdump -vn -i tun0 '(host 192.168.0.100 or host 10.15.119.6)' and icmp
tcpdump: listening on tun0, link-type RAW (Raw IP), capture size 65535 bytes
13:54:30.871403 IP (tos 0x0, ttl 64, id 0, offset 0, flags [DF], proto ICMP (1), length 84)
    10.15.119.6 > 192.168.0.100: ICMP echo request, id 3145, seq 1, length 64
13:54:31.870534 IP (tos 0x0, ttl 64, id 0, offset 0, flags [DF], proto ICMP (1), length 84)
    10.15.119.6 > 192.168.0.100: ICMP echo request, id 3145, seq 2, length 64
13:54:32.879562 IP (tos 0x0, ttl 64, id 0, offset 0, flags [DF], proto ICMP (1), length 84)
    10.15.119.6 > 192.168.0.100: ICMP echo request, id 3145, seq 3, length 64

a second tcpdump on the server:

$ sudo tcpdump -vn -i eth1 '(host 192.168.0.100 or host 10.15.119.6)' and icmp
tcpdump: listening on eth1, link-type EN10MB (Ethernet), capture size 65535 bytes
13:54:30.871429 IP (tos 0x0, ttl 63, id 0, offset 0, flags [DF], proto ICMP (1), length 84)
    10.15.119.6 > 192.168.0.100: ICMP echo request, id 3145, seq 1, length 64
13:54:30.875508 IP (tos 0x0, ttl 64, id 28969, offset 0, flags [none], proto ICMP (1), length 84)
    192.168.0.100 > 10.15.119.6: ICMP echo reply, id 3145, seq 1, length 64
13:54:31.870544 IP (tos 0x0, ttl 63, id 0, offset 0, flags [DF], proto ICMP (1), length 84)
    10.15.119.6 > 192.168.0.100: ICMP echo request, id 3145, seq 2, length 64
13:54:31.870760 IP (tos 0x0, ttl 64, id 28970, offset 0, flags [none], proto ICMP (1), length 84)
    192.168.0.100 > 10.15.119.6: ICMP echo reply, id 3145, seq 2, length 64

and a third tcpdump, this time on the client:

$ sudo tcpdump -vn -i eth0 host 192.168.0.100 and icmp
tcpdump: listening on eth0, link-type EN10MB (Ethernet), capture size 65535 bytes
^C
0 packets captured
0 packets received by filter
0 packets dropped by kernel

IMPORTANT here is something else whch might be helpful, at the client i've run ip route show

$ sudo ip route show
10.15.119.5 dev tun0  proto kernel  scope link  src 10.15.119.6 
10.15.119.1 via 10.15.119.5 dev tun0 
192.168.0.0/24 via 10.15.119.5 dev tun0 
10.21.2.0/24 dev eth0  proto kernel  scope link  src 10.21.2.118  metric 1 
169.254.0.0/16 dev eth0  scope link  metric 1000 
default via 10.21.2.254 dev eth0  proto static

same command at the openvpn server

$ sudo ip route show
10.15.119.2 dev tun0  proto kernel  scope link  src 10.15.119.1 
10.15.119.0/24 via 10.15.119.2 dev tun0 
192.168.0.0/24 dev eth1  proto kernel  scope link  src 192.168.0.101  metric 1 
169.254.0.0/16 dev eth1  scope link  metric 1000 
default via 192.168.0.1 dev eth1  proto static

openvpn version:

$ openvpn --version OpenVPN 2.1.0 x86_64-pc-linux-gnu [SSL] [LZO2] [EPOLL] [PKCS11] [MH] [PF_INET6] [eurephia] built on Jul 12 2010 Originally developed by James Yonan Copyright (C) 2002-2009 OpenVPN Technologies, Inc.

operating system is Ubuntu 10.10 x86_64

Why do i get on the client log:

ue May 31 14:45:41 2011 /sbin/ifconfig tun0 10.15.119.6 pointopoint 10.15.119.5 mtu 1500

Tue May 31 14:45:41 2011 /sbin/route add -net 192.168.0.0 netmask 255.255.255.0 gw 10.15.119.5

Tue May 31 14:45:41 2011 /sbin/route add -net 10.15.119.1 netmask 255.255.255.255 gw 10.15.119.5

whats that about a 255.255.255.255 mask for the virtual network?

@skrewler, this is the result of netstat:

first, from the client when the openvpn is running:

$ netstat -rn
Kernel IP routing table
Destination     Gateway         Genmask         Flags   MSS Window  irtt Iface
10.15.119.5     0.0.0.0         255.255.255.255 UH        0 0          0 tun0
10.15.119.1     10.15.119.5     255.255.255.255 UGH       0 0          0 tun0
192.168.0.0     10.15.119.5     255.255.255.0   UG        0 0          0 tun0
10.21.2.0       0.0.0.0         255.255.255.0   U         0 0          0 eth0
169.254.0.0     0.0.0.0         255.255.0.0     U         0 0          0 eth0
0.0.0.0         10.21.2.254     0.0.0.0         UG        0 0          0 eth0


$ ifconfig -a
eth0      Link encap:Ethernet  HWaddr 08:00:27:0c:86:1c  
          inet addr:10.21.2.118  Bcast:10.21.2.255  Mask:255.255.255.0
          inet6 addr: fe80::a00:27ff:fe0c:861c/64 Scope:Link
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:22701 errors:0 dropped:0 overruns:0 frame:0
          TX packets:12806 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000 
          RX bytes:2855655 (2.8 MB)  TX bytes:1224261 (1.2 MB)

lo        Link encap:Local Loopback  
          inet addr:127.0.0.1  Mask:255.0.0.0
          inet6 addr: ::1/128 Scope:Host
          UP LOOPBACK RUNNING  MTU:16436  Metric:1
          RX packets:8 errors:0 dropped:0 overruns:0 frame:0
          TX packets:8 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:0 
          RX bytes:480 (480.0 B)  TX bytes:480 (480.0 B)

tun0      Link encap:UNSPEC  HWaddr 00-00-00-00-00-00-00-00-00-00-00-00-00-00-00-00  
          inet addr:10.15.119.6  P-t-P:10.15.119.5  Mask:255.255.255.255
          UP POINTOPOINT RUNNING NOARP MULTICAST  MTU:1500  Metric:1
          RX packets:0 errors:0 dropped:0 overruns:0 frame:0
          TX packets:0 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:100 
          RX bytes:0 (0.0 B)  TX bytes:0 (0.0 B)

and the client.conf:

dev tun0
remote my.server.com
tls-client
pull
ca keys/ca.crt
cert keys/client.crt
key keys/client.key
ns-cert-type server
status logs/openvpn-status.log
log         logs/openvpn.log
comp-lzo
verb 4

second, from the openvpn server

$ netstat -rn
Kernel IP routing table
Destination     Gateway         Genmask         Flags   MSS Window  irtt Iface
10.15.119.2     0.0.0.0         255.255.255.255 UH        0 0          0 tun0
10.15.119.0     10.15.119.2     255.255.255.0   UG        0 0          0 tun0
192.168.0.0     0.0.0.0         255.255.255.0   U         0 0          0 eth1
169.254.0.0     0.0.0.0         255.255.0.0     U         0 0          0 eth1
0.0.0.0         192.168.0.1     0.0.0.0         UG        0 0          0 eth1

server.conf

dev tun
server 10.15.119.0 255.255.255.0
ifconfig-pool-persist ipp.txt
push "route 192.168.0.0 255.255.255.0"
tls-server
dh keys/dh1024.pem
ca keys/ca.crt
cert keys/openvpn-server-key.crt
key keys/openvpn-server-key.key
user nobody
group nogroup
status openvpn-status.log
log         logs/openvpn.log
comp-lzo
verb 4

with the above setup i am able to:

1) ping from the client to 192.168.0.101 (the openvpn server) 2) ping from the openvpnserver to 10.15.119.6 (the client)

what i am not able to do is ping 192.168.0.100 (secondary LAN server) from the client.

192.168.0.100 actually does reply to the client as tcpdump at the openserver shows, but somehow those packets does not make it back to the client

routing networking openvpn tun

8 Answers

  1. You will need to push a route through to the clients. This is done using the "push" option in the server config file.

    By default the OpenVPN server will only push a route to itself.

    In general, when setting up a VPN server, it is a good idea to have the VPN working on a separate subnet, so that you make your routing easier, and also to make your firewall setup easier. Example:

    The server running the OpenVPN server has an internal IP address of 10.15.119.1. Its public IP address is 123.1.2.3. And your entire internal network is on 10.15.119.0/24. You would then set up the OpenVPN server to run on 10.15.120.0/24, which will give you up to 63 possible client connections (each connection requires a small subnet of 4 IP addresses). The first client that connects will get IP address 10.15.120.5. If you now push the route to 10.15.119.0/24 , the client will add a route to its routing table so that all traffic for this subnet goes into the tunnel. The OpenVPN server will then fro3ward this traffic into its private ethernet connection.

    Read the man page of OpenVPN (or the documentation on the internet) for the exact details of how to push a route.

    • 2

  2. Perhaps I'm not understanding properly, but does the equipment that you're trying to reach behind the VPN server have a configured route that points to the OpenVPN client subnet?

    If you're running OpenVPN on a system that's not your default gateway and requires a separate route, those servers wouldn't be able to get packets back to your clients.

    The pings originating from your OpenVPN server are being sent from an interface that the equipment can route to, but perhaps the pings going back to the clients have no route to get back if the other servers don't know about that route.

    This might be irrelevant if you're NAT'ing your client traffic at the server, but I haven't seen anything to indicate that in the configs you posted.

    • 2
  3. Best Answer

    I went through the responses and I think I'm savvy to where you're at with all this.

    Lets do some simple checks to narrow down the issue:

    From one of the OpenVPN clients that is unable to ping a 192.168.0.x host: netstatn -rn Also give us ifconfig -a for *nix or ipconfig /all ping <openvpn server external 10.21.x address> ping <openvpn 10.15.x address

    From the openvpn server: netstatn -rn ping <a 192.168.0.x host> ping <a 10.15.x host> ping <a 10.21.x host>

    Also, your current openvpn server config and client config probably at /etc/openvpn/server.conf and on the client machine /etc/openvpn/<hostname>.conf or c:\program files\openvpn\config\<hostname.conf> or .ovpn

    I have a similar setup. On my OpenVPN server I have the equiv of this iptables rule (changed hostmask/interface to what your values should be):

    # Generated by iptables-save v1.4.4 
*nat
:PREROUTING ACCEPT [5:332]
:POSTROUTING ACCEPT [5:740]
:OUTPUT ACCEPT [5:740]
-A POSTROUTING -s 10.15.119.0/2 -o eth1 -j MASQUERADE
COMMIT

    Looks like your problem is most definately because you're missing iptable_nat.

    # lsmod | grep nat
iptable_nat             5011  1 
nf_nat                 19101  2 ipt_MASQUERADE,iptable_nat
nf_conntrack_ipv4      12548  3 iptable_nat,nf_nat
nf_conntrack           72270  4 ipt_MASQUERADE,iptable_nat,nf_nat,nf_conntrack_ipv4
ip_tables              17942  2 iptable_nat,iptable_filter
x_tables               21613  3 ipt_MASQUERADE,iptable_nat,ip_tables

    modprobe iptable_nat or try with the -a parameter.

    • 2

  4. Try this:

    Add an iptables SNAT rule on your server.

    iptables -t nat -A POSTROUTING -s 10.15.119.0/24 -o eth0 -j SNAT --to-source 10.21.2.118

    This will give any VPN client IP connections to your other servers in that network a working/routed NAT to go back to.

    • 2

  5. Why don't you flush the iptables rules completely, to get that possibility out of the way. What about iptables on the client? Flush those too.

    iptables --flush
iptables --table nat --flush
iptables --delete-chain
iptables --table nat --delete-chain
iptables -P FORWARD ACCEPT
iptables -P INPUT ACCEPT
iptables -P OUTPUT ACCEPT

    Then run a cleaner tcpdump on the openvpn server, while pinging from the client to 192.168.0.100:

    tcpdump -vn -i tun0 '(host 192.168.0.100 or host 10.15.119.6)' and icmp

    Also run a second dump on the server at the same time:

    tcpdump -vn -i eth1 '(host 192.168.0.100 or host 10.15.119.6)' and icmp

    A third dump on your client:

    tcpdump -vn -i eth0 host 192.168.0.100 and icmp

    It does look like the ping reaches 192.168.0.100, the reply reaches openvpn, but not your client. But are you sure the client isn't dropping the reply? The first and third tcpdump will verify that.

    • 1

  6. The setup you're trying to accomplish is a somewhat esoteric request, and is addressed by a feature of OpenVPN which is not very well known.

    Most VPN setups are configured in such a way whereby the client connecting to the VPN server is the last link in the chain, and there are no other computers or networks behind it which need to be accessible on the VPN. In your scenario, there are networks behind the VPN server as well as the VPN clients, and these networks need to be able to talk to one another directly. There are a number of ways to accomplish this:

    Option 1: Configure source NAT at each client. This is not the preferred option, as it adds overhead on the client-side, as well as requiring each client to be individually set up for source NAT. Maintaining such a setup on a large number of networks will be a nightmare.

    Option 2: Use the iroutes feature provided by OpenVPN. Using iroutes you are able to explicitly specify the networks behind each node on the network, and thus enable the various networks to talk to one another through OpenVPN's internal routing. The primary benefit of using iroutes over source NAT is that there is no client overhead, and the configuration is all performed on the VPN server only. Bear in mind that you are still required to specify routes to be pushed on the VPN server - adding iroutes must be performed in addition to this and serves the sole purpose of defining the network ranges behind each VPN node.

    Since iroutes are not a trivial topic, I advise reading the following pages. If you have specific problems with setting up iroutes, please ask those questions here.

    http://www.secure-computing.net/wiki/index.php/OpenVPN/Routing http://backreference.org/2009/11/15/openvpn-and-iroute

    • 0

  7. I did what you are asking for, I did some things different. For one, I used a tap-device.

    Take a look below:

    server.conf

    port 1194
proto udp
dev tap0
ca /etc/openvpn/keys/ca.crt
cert /etc/openvpn/keys/server.crt
key /etc/openvpn/keys/server.key  # This file should be kept secret
dh /etc/openvpn/keys/dh1024.pem
ifconfig-pool-persist ipp.txt
server-bridge 192.168.220.1 255.255.255.0 192.168.220.90 192.168.220.100  # GATEWAY - NETMASK - START DHCP - END DHCP
push "route 192.168.220.0 255.255.255.0"
client-to-client
keepalive 10 120
comp-lzo
max-clients 20
persist-key
persist-tun
status openvpn-status.log
verb 3

    client.conf

    remote xxx.xxx.xxx.xxx 1194 udp
pull
tls-client
persist-key
ca ca.crt
nobind
persist-tun
cert cert.crt
comp-lzo
dev tap
key key.key
resolv-retry infinite
    • 0

  8. Try removing the "up ./office.up" from your server configuration file and restarting OpenVPN. It is not necessary (the openvpn daemon will create the routes for the network defined by the "server" directive anyway) and some screwup might prevent the packets to your clients from being routed correctly.

    • 0