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L2TP and proxy-arp

Mon Sep 12, 2011 12:48 pm

Hi all,

Bit of a problem here...

Got a RB acting as a LNS in a data centre with a /24. I would like to allocate one address from this pool to an L2TP client.

Both the LNS and the client are running ROS 5.6. Both have only one ethernet port.

LNS:
IP 198.51.100.254/24
gw 198.51.100.1

Client:
ether1 IP 203.0.113.254/24
gw 203.0.113.1

I want to give the L2TP tunnel the IP address 198.51.100.253.

I can get the connection working perfectly when using addresses from a different network block (say using 192.168.0.0/24 and adding routes as appropriate), but not when I want to allocate one of the public /24s to the client. The tunnel comes up and shows the correct address, but 198.51.100.253 is not pingable/routable from anywhere other than the LNS.

In any other situation, I would configure proxy-arp on the LNSs ether1, but as soon as I do in this case, the LNS becomes unresponsive to all connections until the proxy-arp setting is removed.

Any ideas?
Nicholas Barnes BSc(hons)
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hedele
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Re: L2TP and proxy-arp

Mon Sep 12, 2011 3:43 pm

Well... it is a rather dirty fix, but you could add the 198.51.100.253 address to your LNS'es ether1, give your L2TP client a private (192...) address,
and then NAT the whole official IP through using two netmap rules in /ip firewall nat

I also noticed, that activating proxy-arp while an interface is running often causes routerboards to stop working, until you either reboot, or disable and enable the corresponding ethernet interface - however i am not sure why this is happening.
 
vk7zms
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Re: L2TP and proxy-arp

Mon Jun 25, 2012 2:49 pm

Hi Nick - a little off your topic, but I would like to set up an RB1100 as a LNS server. I can set up the L2TP server easy enough, and have set up lots of PPPoE servers for Ethernet based networks. The bit I am missing is how to get the PPPoE server running over the incoming L2TP tunnels. If you have a spare minute for a "30 words or less" answer, it would be greatly appreciated. Not looking for a config - just some guidance on how to make the PPPoE and L2TP work together.

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