It may also be useful to use L2TP just as any other tunneling protocol with or without encryption. The L2TP standard says that the most secure way to encrypt data is using L2TP over IPsec (Note that it is default mode for Microsoft L2TP client) as all L2TP control and data packets for a particular tunnel appear as homogeneous UDP/IP data packets to the IPsec system.
Multilink PPP (MP) is supported in order to provide MRRU (the ability to transmit full-sized 1500 and larger packets) and bridging over PPP links (using Bridge Control Protocol (BCP) that allows to send raw Ethernet frames over PPP links). This way it is possible to setup bridging without EoIP. The bridge should either have an administratively set MAC address or an Ethernet-like interface in it, as PPP links do not have MAC addresses.
L2TP includes PPP authentication and accounting for each L2TP connection. Full authentication and accounting of each connection may be done through a RADIUS client or locally.
MPPE 40bit RC4 and MPPE 128bit RC4 encryption are supported.
L2TP traffic uses UDP protocol for both control and data packets. UDP port 1701 is used only for link establishment, further traffic is using any available UDP port (which may or may not be 1701). This means that L2TP can be used with most firewalls and routers (even with NAT) by enabling UDP traffic to be routed through the firewall or router.
Quick example
This example demonstrates how to set up L2TP client with username "l2tp-hm", password "123" and server 10.1.101.100
[admin@dzeltenais_burkaans] /interface l2tp-client>add name=l2tp-hm user=l2tp-hm password=123 \
\... connect-to=10.1.101.100 disabled=no
[admin@dzeltenais_burkaans] /interface l2tp-client> print detail
Flags: X - disabled, R - running
0 name="l2tp-hm" max-mtu=1460 max-mru=1460 mrru=disabled
connect-to=10.1.101.100 user="l2tp-hm" password="123"
profile=default-encryption add-default-route=no dial-on-demand=no
allow=pap,chap,mschap1,mschap2
L2TP Server
This sub-menu shows interfaces for each connected L2TP clients.
An interface is created for each tunnel established to the given server. There are two types of interfaces in L2TP server's configuration
- Static interfaces are added administratively if there is a need to reference the particular interface name (in firewall rules or elsewhere) created for the particular user.
- Dynamic interfaces are added to this list automatically whenever a user is connected and its username does not match any existing static entry (or in case the entry is active already, as there can not be two separate tunnel interfaces referenced by the same name).
Dynamic interfaces appear when a user connects and disappear once the user disconnects, so it is impossible to reference the tunnel created for that use in router configuration (for example, in firewall), so if you need persistent rules for that user, create a static entry for him/her. Otherwise it is safe to use dynamic configuration.
To enable L2TP server:
[admin@MikroTik] interface l2tp-server server> set enabled=yes
[admin@MikroTik] interface l2tp-server server> print
enabled: yes
max-mtu: 1460
max-mru: 1460
mrru: disabled
authentication: pap,chap,mschap1,mschap2
default-profile: default-encryption
[admin@MikroTik] interface l2tp-server server>
Monitoring
Monitor command can be used to monitor status of the tunnel on both client and server.
[admin@dzeltenais_burkaans] /interface l2tp-client> monitor 0
status: "connected"
uptime: 7h24m18s
idle-time: 6h21m4s
encoding: "MPPE128 stateless"
mtu: 1460
mru: 1460
Application Examples
Connecting Remote Client
The following example shows how to connect a computer to a remote office network over L2TP encrypted tunnel giving that computer an IP address from the same network as the remote office has (without any need of bridging over EoIP tunnels)
Consider following setup:
Office router is connected to internet through ether1. Workstations are connected to ether2. Laptop is connected to the internet and can reach Office router's public IP (in our example it is 192.168.80.1).
First step is to create a user
[admin@RemoteOffice] /ppp secret> add name=Laptop service=l2tp password=123
local-address=10.1.101.1 remote-address=10.1.101.100
[admin@RemoteOffice] /ppp secret> print detail
Flags: X - disabled
0 name="Laptop" service=l2tp caller-id="" password="123" profile=default
local-address=10.1.101.1 remote-address=10.1.101.100 routes==""
[admin@RemoteOffice] /ppp secret>
Notice that L2TP local address is the same as routers address on local interface and remote address is from the same range as local network (10.1.101.0/24).
Next step is to enable L2TP server and L2TP client on the laptop.
[admin@RemoteOffice] /interface l2tp-server server> set enabled=yes
[admin@RemoteOffice] /interface l2tp-server server> print
enabled: yes
max-mtu: 1460
max-mru: 1460
mrru: disabled
authentication: mschap2
default-profile: default-encryption
[admin@RemoteOffice] /interface l2tp-server server>
L2TP client from the laptop should connect to routers public IP which in our example is 192.168.80.1.
Please, consult the respective manual on how to set up a L2TP client with the software you are using.
At this point (when L2TP client is successfully connected) if you will try to ping any workstation from the laptop, ping will time out, because Laptop is unable to get ARPs from workstations. Solution is to set up proxy-arp on local interface
[admin@RemoteOffice] interface ethernet> set ether2 arp=proxy-arp
[admin@RemoteOffice] interface ethernet> print
Flags: X - disabled, R - running
# NAME MTU MAC-ADDRESS ARP
0 R ether1 1500 00:30:4F:0B:7B:C1 enabled
1 R ether2 1500 00:30:4F:06:62:12 proxy-arp
[admin@RemoteOffice] interface ethernet>
After proxy-arp is enabled client can now successfully reach all workstations in local network behind the router.
Site-to-Site L2TP
The following is an example of connecting two Intranets using a L2TP tunnel over the Internet.
Consider following setup:
Office and Home routers are connected to internet through ether1, workstations and laptops are connected to ether2. Both local networks are routed through L2TP client, thus they are not in the same broadcast domain. If both networks should be in the same broadcast domain then you need to use BCP and bridge L2TP tunnel with local interface.
First step is to create a user
[admin@RemoteOffice] /ppp secret> add name=Home service=l2tp password=123
local-address=172.16.1.1 remote-address=172.16.1.2 routes="10.1.202.0/24 172.16.1.2 1"
[admin@RemoteOffice] ppp secret> print detail
Flags: X - disabled
0 name="Home" service=l2tp caller-id="" password="123" profile=default
local-address=172.16.1.1 remote-address=172.16.1.2 routes=="10.1.202.0/24 172.16.1.2 1"
[admin@RemoteOffice] /ppp secret>
Notice that we set up L2TP to add route whenever client connects. If this option is not set, then you will need static routing configuration on the server to route traffic between sites through L2TP tunnel.
Next step is to enable L2TP server on the office router and configure L2TP client on the Home router.
[admin@RemoteOffice] /interface l2tp-server server> set enabled=yes
[admin@RemoteOffice] /interface l2tp-server server> print
enabled: yes
max-mtu: 1460
max-mru: 1460
mrru: disabled
authentication: mschap2
default-profile: default-encryption
[admin@RemoteOffice] /interface l2tp-server server>
[admin@Home] /interface l2tp-client> add user=Home password=123 connect-to=192.168.80.1 disabled=no
[admin@Home] /interface l2tp-client> print
Flags: X - disabled, R - running
0 R name="l2tp-out1" max-mtu=1460 max-mru=1460 mrru=disabled connect-to=192.168.80.1 user="Home"
password="123" profile=default-encryption add-default-route=no dial-on-demand=no
allow=pap,chap,mschap1,mschap2
[admin@Home] /interface l2tp-client>
On home router if you wish traffic for the remote office to go over tunnel you will need to add a specific static route as follows:
[admin@Home] /ip route> add dst-address=10.1.101.0/24 gateway=l2tp-out1
After tunnel is established and routes are set, you should be able to ping remote network.
L2TP/IpSec setup
This example demonstrates how to easily setup L2TP/IpSec server on Mikrotik router (with installed 6.16 or newer version) for road warrior connections (works with Windows, Android And iPhones).
First step is to enable L2TP server:
/interface l2tp-server server
set enabled=yes use-ipsec=yes ipsec-secret=mySecret default-profile=default
Now what it does is enables L2TP server and creates dynamic ipsec peer iwth specified secret
[admin@MikroTik] /ip ipsec peer> print
0 D address=0.0.0.0/0 local-address=0.0.0.0 passive=yes port=500
auth-method=pre-shared-key secret="123" generate-policy=port-strict
exchange-mode=main-l2tp send-initial-contact=yes nat-traversal=yes
hash-algorithm=sha1 enc-algorithm=3des,aes-128,aes-192,aes-256
dh-group=modp1024 lifetime=1d dpd-interval=2m dpd-maximum-failures=5
/ip pool add name=vpn-pool range=192.168.99.2-192.168.99.100
/ppp profile
set default local-address=192.168.99.1 remote-address=vpn-pool
/ppp secret
add name=user1 password=123
add name=user2 password=234
If there are strict firewall policies, do not forget to add rules which accepts l2tp and ipsec.
/ip firewall filter
add chain=input protocol=udp port=1701,500,4500
add chain=input protocol=ipsec-esp
Now router is ready to accept L2TP/IpSec client connections.
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