L2TP Overview

On special request you can have an L2TP login in to AAISP - pricing is based on the usage, and is currently priced the same as usage costs on AAISP 'Be' lines.

FireBrick FB2500/2700 Fully Loaded

The FireBrick can connect as an L2TP client for fallback and for its main connection. One thing to watch out for is making sure that the FB doesn't set its own gateway to be the tunnel (which would logically send tunnel packets up the tunnel, which is horrid). You can get around this by using separate routing tables.

This example is for L2TP being the main connection:

<interface name="WAN"
           port="WAN1"
           table="1"
           comment="DHCP client">

<l2tp>
 <outgoing name="AAISP"
           ip="90.155.53.19"
           graph="AAISP"
           table="1"
           payload-table="0"
           username="example@a"
           password="secret"
           tcp-mss-fix="true"
           comment="L2TP tunnel to AAISP"/>
</l2tp>

You can set to fall back to NAT if the tunnel is down. Traffic on routing table 0 won't have a default gateway if the L2TP is down, so will match this rule set that has target interface "nowhere":

<rule-set name="Fallback"
          target-interface="nowhere"
          no-match-action="continue"
          comment="NAT fallback if can't establish L2TP">
 <rule name="NAT"
       set-nat="true"
       set-table="1"
       action="accept"/>
</rule-set>

If the L2TP is being used for fallback, you are probably better off setting the routing table for the L2TP to something other than 0. Remember firewall rules only apply to single routing tables.

RouterBoard

Connecting to L2TP with a RouterBoard was pretty seamless - put in the L2TP server IP, username and password and it just connects. Have to mess about with IP / Route and NAT / masquerading a bit to get devices behind the RouterBoard online but that all depends on whether you have an additional IP block and what you want to do with it anyway.

Windows 7

Connecting with Windoze 7 was almost as easy except that the default connection settings don't work. You have to edit the connection properties and on the Security tab change 'Type of VPN:' to 'Layer 2 Tunneling Protocol with IPsec (L2TP/IPSec)' otherwise it only tries PPTP, and change 'Data encryption:' to 'Optional encryption (connect even if no encryption)' as it doesn't like A+A's certificate (because RevK declines to use a root certification authority recognised by Microsoft, or is it that Microsoft declines to recognise the root certification authority chosen by RevK). I guess the alternative would probably be to add the root certificate to the machine in question. Anyway, with those two changes it works fine.

Watch out if you are using IPv6. It seems that Win7 negotiates a non-routable IPv6 address with the LNS. You have to discard this address and manually configure one of your routed IPv6 addresses. ipconfig /release6 is your friend here.

Cisco Routers

Cisco routers running IOS 12.3(2)T and later support L2TP client initiated tunneling which allows the router to establish an L2TP tunnel to A&A's L2TP server.

Most of the information required was gleaned from here: [1] plus a bit of trial and error and some packet capturing of good and bad L2TP sessions.

I have tested this on a Cisco 837 router running 12.3(11)YZ2, a 2821 running 12.4(15)T10 SPServices and a 2801 running 12.4(24)T3 ADVIPServices

Caveats:

- You will need to sanity check routing in your particular environment. This is especially important if you choose to use ppp ipcp route default on the l2tp tunnel. It's safest to make sure that you have a static route set to the L2TP server.

- I haven't tested this for IPV6 yet.

- This is "early release" information - I haven't yet used this in anger over a long period of time but will try to remember to come back and update if I find any major issues.

- This config snippet contains no security settings - be sure to configure some!

- I've used the IP address of the L2TP server rather than the DNS address - this is obviously at risk of change .

- You need to be running IP CEF on the router

Config:

Replace <whatever> with the appropriate information for your connection

ip cef
l2tp-class lc-aaisp

pseudowire-class pc-aaisp
 encapsulation l2tpv2
 protocol l2tpv2 lc-aaisp
 ip local interface <interface that l2tp connection should go out from>

interface Virtual-PPP9797
 shutdown
 ip address negotiated
 no cdp enable
 ppp authentication chap callin
 ppp chap hostname <l2tp line login eg stzzz@a.2>
 ppp chap password 0 <site password>
 ppp direction callout
 ppp pap refuse
 pseudowire 90.155.53.19 10 pw-class pc-aaisp
 

Once the interface is configured you can issue a no shut on it to bring it up.

Debugging:

debug ppp authentication and debug ppp negotiation are your friends... In particular if you see "Circuit ID not set - contact support" in the authentication debug, contact A&A support to get them to fix your L2TP login.

Once the connection is up, you should see the virtual PPP interface configured with the static IP that is assigned to it in clueless.

If you get stuck, pop into the IRC channel and see if I'm around (basil_uk) and I'll help if possible.

Other Hardware

The TL-WR741ND router works, although it can only do NAT, but is very cheap.