problem with connecting another subnet (destination net unknown)

Thu Feb 7 20:38:04 CET 2019

Hello tinc mailing list! Nice to be accepted here :)

So I've been using tinc for a while just for itself and now I would like
to use it to route to another network. To be exact I have two tinc
networks with a "central node" that is connected to both tincs:

tiutl: 172.16.0.0/24
tiosp: 172.16.1.0/24

I'm doing that because I can then do fancy firewalling on that central node.

The setup looks like this:

web <- tinc "tiosp" -> gateway <- tinc "tiutl" -> backup

Server web: tiosp with 172.16.1.10
Server gateway: tiutil with 172.16.0.5 as well as tiosp with 172.16.1.5
Server backup: tiutl with 172.16.0.11

Now from web I can ping gateway on both 172.16.0.5 as well as
172.16.1.5. In tcpdump I can see that I could also ping 172.16.0.11
(backup), but backup does not know how to route the packets back :/

From backup I can ping 172.16.0.5 of course ("normal" tinc), but not
172.16.1.5 (gateways tinc IP in the other tinc). In tcpdump I can see
that no icmp packets are reaching gateway.

## The backup server (tinc IP 172.16.0.11) in the tinc "tiutl" has a
route to 172.16.0.0/24 and 172.16.1.0/24 via tinc "tiutl"

root at backup-1:~# netstat -rn
Kernel IP routing table
Destination     Gateway         Genmask         Flags   MSS Window  irtt
Iface
0.0.0.0         85.184.249.1    0.0.0.0         UG        0 0          0
eth0
10.0.0.0        0.0.0.0         255.255.255.0   U         0 0          0
eth1
85.184.249.1    0.0.0.0         255.255.255.255 UH        0 0          0
eth0
172.16.0.0      0.0.0.0         255.255.255.0   U         0 0          0
tiutl
172.16.1.0      0.0.0.0         255.255.255.0   U         0 0          0
tiutl

## The backup servers tinc.conf

root at backup-1:~# cat /etc/tinc/tiutl/tinc.conf
Name = backup_1
Interface = tiutl
Device = /dev/net/tun
AddressFamily = ipv4
Port = 655
ConnectTo = gateway_1
ConnectTo = gateway_2
ConnectTo = git_1

## The backup servers tinc-up script

root at backup-1:~# cat /etc/tinc/tiutl/tinc-up
ip link set tiutl up
ip address add 172.16.0.11/24 dev tiutl                     <- works
ip route add 172.16.1.0/24 via 172.16.0.5 dev tiutl    <- doesn't work

## The backup servers tinc.conf

root at backup-1:~# cat /etc/tinc/tiutl/hosts/gateway_1
Address = 40.10.70.200  # the pubilc connect_to IP
Port = 655
Subnet = 172.16.0.5/32
Subnet = 172.16.1.0/24

-----BEGIN RSA PUBLIC KEY-----
-----END RSA PUBLIC KEY-----

## From backup, when I try to ping the "gateway" server in the "tiutl"
tinc network, this works:

root at backup-1:~# ping -c 1 172.16.0.5
PING 172.16.0.5 (172.16.0.5) 56(84) bytes of data.
64 bytes from 172.16.0.5: icmp_seq=1 ttl=64 time=7.85 ms

--- 172.16.0.5 ping statistics ---
1 packets transmitted, 1 received, 0% packet loss, time 0ms
rtt min/avg/max/mdev = 7.853/7.853/7.853/0.000 ms

## However pinging the IP the gateway server has in the other network
gives me dest net unknown:

root at backup-1:~# ping -c 1 172.16.1.5
PING 172.16.1.5 (172.16.1.5) 56(84) bytes of data.
From 172.16.1.5 icmp_seq=1 Destination Net Unknown

--- 172.16.1.5 ping statistics ---
1 packets transmitted, 0 received, +1 errors, 100% packet loss, time 0ms

Also here, on gateway, no icmp packets show up in tcpdump.. Using
tcpdump on backup does make it look like gateway is answering, but it
isnt.. :/ Here is the tcpdump from backup and gateway while backup pings
gateway's "other" tinc IP:

root at backup-1:~# ping 172.16.1.5
PING 172.16.1.5 (172.16.1.5) 56(84) bytes of data.
From 172.16.1.5 icmp_seq=1 Destination Net Unknown

root at backup-1:/etc/tinc/tiutl# tcpdump -i any icmp -n
tcpdump: verbose output suppressed, use -v or -vv for full protocol decode
listening on any, link-type LINUX_SLL (Linux cooked), capture size
262144 bytes
20:26:22.990261 IP 172.16.0.11 > 172.16.1.5: ICMP echo request, id 3012,
seq 5, length 64
20:26:22.990322 IP 172.16.1.5 > 172.16.0.11: ICMP net 172.16.1.5
unreachable - unknown, length 92

root at gateway-1:/etc/tinc/tiutl# tcpdump -i any icmp -n
(nothing shows up here)

## Now the interesting part is that for some reasons the same thing is
working for the web (172.16.1.10) server (and I can just not find the
difference)

root at web-1:~# ping 172.16.0.5
PING 172.16.0.5 (172.16.0.5) 56(84) bytes of data.
64 bytes from 172.16.0.5: icmp_seq=1 ttl=64 time=7.22 ms

root at web-1:~# ping 172.16.1.5
PING 172.16.1.5 (172.16.1.5) 56(84) bytes of data.
64 bytes from 172.16.1.5: icmp_seq=1 ttl=64 time=7.47 ms

## From web (172.16.1.10), I can send icmp's to backup (172.16.0.11)
(backup just doesn't know where to send the answer)

root at web-1:~# ping -c 1 172.16.0.11
PING 172.16.0.11 (172.16.0.11) 56(84) bytes of data.

--- 172.16.0.11 ping statistics ---
1 packets transmitted, 0 received, 100% packet loss, time 0ms

## The packets arrive at backup (172.16.0.11)... (so yes I did `echo 1 >
/proc/sys/net/ipv4/ip_forward` on gateway)

root at backup-1:~# tcpdump -i any icmp -n
tcpdump: verbose output suppressed, use -v or -vv for full protocol decode
listening on any, link-type LINUX_SLL (Linux cooked), capture size
262144 bytes
20:20:11.098991 IP 172.16.1.10 > 172.16.0.11: ICMP echo request, id
33274, seq 4, length 64
20:20:11.099024 IP 172.16.0.11 > 172.16.1.10: ICMP echo reply, id 33274,
seq 4, length 64
20:20:11.099046 IP 172.16.1.10 > 172.16.0.11: ICMP net 172.16.1.10
unreachable - unknown, length 92

## Web servers config files (for the web server, everything works as
expected)

root at web-1:~# cat /etc/tinc/tiosp/tinc.conf
Name = web_1
Interface = tiosp
Device = /dev/net/tun
AddressFamily = ipv4
Port = 656
ConnectTo = gateway_1
ConnectTo = gateway_2
ConnectTo = web_1

root at web-1:~# cat /etc/tinc/tiosp/tinc-up
#!/bin/bash
ip link set tiosp up
ip address add 172.16.1.10/24 dev tiosp
ip route add 172.16.0.0/24 via 172.16.1.5 dev tiosp

root at web-1:~# cat /etc/tinc/tiosp/hosts/gateway_1
Address = 40.10.70.240
Port = 656
Subnet = 172.16.1.5/24
Subnet = 172.16.0.0/24

-----BEGIN RSA PUBLIC KEY-----
-----END RSA PUBLIC KEY-----

Maybe I've been looking at this for to long :/ I just can't find the
problem. Sure its something obvious.. ;) Thank you guys in advance!

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