Posts tagged stronswan

strongswan ipsec vpn site to site
posted on 2016-12-02 09:42

This guide was written for debian 8.

network layout

local/left       lan: 192.168.0.0/16
local/left   gateway: 10.0.0.2
remote/right gateway: 10.0.0.3
remote/right     lan: 172.16.0.0/16

Our network, expressed differently:

192.168.0.0/16 --- unencrypted --- 10.0.0.2 === vpn === 10.0.0.3 --- unencrypted --- 172.16.0.0/16

In strongswan it doesn't matter which side is defined in either left or right, but this convention helps:

  • local = left
  • rremote = right

ipsec settings for the tunnel

These may be somewhat arbitrarily, but we got to use something:

phase1:
ikev1 / aes256 / sha2 / dh5 / 86400s (24h statt 8h)

phase2:
esp / aes256 / sha2 / dh5 / 3600s

( protocol / encryption / hashing / DH group or PFS if present / lifetime )

install

apt-get install strongswan libcharon-extra-plugins

define PSK

Add to /etc/ipsec.secrets:

10.0.0.2 10.0.0.3 : PSK "thatsmydamnsecretPSKwhichreallyshouldbearandomsting"

setup tunnel

/etc/ipsec.conf:

config setup

conn %default
    keyexchange=ikev1
    keyingtries=%forever
    leftauth=psk
    rightauth=psk
    auto=start

conn myconfig-main
    left=10.0.0.2
    ike=aes256-sha256-modp1536
    ikelifetime=86400s
    esp=aes256-sha256-modp1536
    lifetime=3600s

conn myconfig1
    right=10.0.0.3
    leftsubnet=192.168.0.0/24
    rightsubnet=172.16.0.0/16
    also=myconfig-main

include /var/lib/strongswan/ipsec.conf.inc

That way you can add additional phase2 entries analoguous to conn myconfig1.

%default is valid for everything, myconfig-main is included via auto=myconfig-main into other connection definitions.

test

service ipsec restart

These might help:

tail -f /var/log/syslog
watch -n1 -d ipsec statusall

Ping from withing your lan a host inside the remote lan.

For watching the pings, the ones you want to see will be colored:

tcpdump -D # discern the interface you need to have a look at, usually eth0 / 1
tcpdump -nli 1 icmp | grep -color -e $ -e 192.168.

routing rules are automatically added by strongswan, do service ipsec restart while watching:

watch -n1 -d "ip ru; ip r l t 220"

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