Home A - Z
Page Index

An Otter Wiki

Blame

92674b Samuli Seppänen 2025-02-28 14:01:28 1 
**Avoid routing conflicts**
2
3
4
The following applies to a routed TUN setup which should just about always be the way to setup OpenVPN.
5
6
In order to avoid routing conflicts one should choose subnets carefully for the networks **under ones control**.
7
These should be RFC 1918 compliant, https://tools.ietf.org/html/rfc1918.
8
9
```
10
10.0.0.0 - 10.255.255.255 (10/8 prefix)
11
172.16.0.0 - 172.31.255.255 (172.16/12 prefix)
12
192.168.0.0 - 192.168.255.255 (192.168/16 prefix)
13
```
14
681932 Samuli Seppänen 2025-02-28 14:06:07 15
![Visualization of OpenVPN routed TUN with subnet topology](./arc1.png "Routed TUN - Topology subnet")
f7f147 Samuli Seppänen 2025-02-28 14:05:56 16
92674b Samuli Seppänen 2025-02-28 14:01:28 17
Traveling clients like laptops and mobile phones mostly have no control over the network they reside.
18
In those cases it becomes even more important to choose **uncommon** subnets.
19
20
In the simplest form there are three networks involved, see Figure 1:
21
1. The Server side subnet
22
2. The Tunnel subnet
23
3. The Client side subnet
24
f7f147 Samuli Seppänen 2025-02-28 14:05:56 25
26
92674b Samuli Seppänen 2025-02-28 14:01:28 27
Figure 1
28
29
There may be no overlap between 1, 2 and 3.
30
Basically, normal routing applies which should now be obvious to the network admin.
31
32
The following (incomplete) list is comprised of default settings for routers/acces points/switches/etc.
33
These are common subnets one should try to avoid:
34
35
```
36
10.0.0
37
10.0.1
38
10.1.1
39
10.1.10
40
10.2.0
41
10.8.0
42
10.10.1
43
10.90.90
44
10.100.1
45
10.255.255
46
47
169.254 # APIPA #
48
49
172.16.0
50
172.16.16
51
172.16.42
52
172.16.68
53
54
172.19.3
55
56
172.20.10 # IPhone built-in hotspot #
57
58
192.168.0
59
192.168.1
60
192.168.2
61
192.168.3
62
192.168.4
63
192.168.5
64
192.168.6
65
192.168.7
66
192.168.8
67
192.168.9
68
192.168.10
69
192.168.11
70
192.168.13
71
192.168.15
72
192.168.16
73
192.168.18
74
192.168.20
75
192.168.29
76
192.168.30
77
192.168.31
78
192.168.33
79
192.168.39
80
192.168.40
81
192.168.42 # Android USB tethering #
82
192.168.43 # Android built-in hotspot #
83
192.168.50
84
192.168.55
85
192.168.61
86
192.168.62
87
192.168.65
88
192.168.77
89
192.168.80
90
192.168.84 # Google WiFi
91
192.168.85 # Google WiFi
92
192.168.86 # Google WiFi
93
192.168.88
94
192.168.98
95
192.168.99
96
192.168.100
97
192.168.101
98
192.168.102
99
192.168.111
100
192.168.123
101
192.168.126
102
192.168.129
103
192.168.137 # Windows Phone built-in hotspot #
104
192.168.168
105
192.168.178
106
192.168.190
107
192.168.199
108
192.168.200
109
192.168.220
110
192.168.223
111
192.168.229
112
192.168.240
113
192.168.245
114
192.168.251
115
192.168.252
116
192.168.254
117
118
200.200.200
119
```
120
121
122
123
November 5 2019 by Pippin