Ubuntu – LAN and WAN at the same cable

iptablesnat;routingUbuntuvlan

Can I connect LAN and Internet using the same cable?

  LAN computers ------\
  Ubuntu server ------Switch
  ADSL Router --------/

I want to make LAN computers 192.168.0.2-50, server will have real IP 192.168.0.1 and some "virtual" IP 192.168.1.2. ADSL router will have 192.168.1.1.

So all traffic will go via server where I can make statistics, filters etc.

Best Answer

yes, you can. it's called router-on-the-stick configuration, just make sure your switch supports tagged vlans and put wan [adsl] and lan in separate vlans, connect trunk with tagging to the linux box.

under linux you treat separate vlans like they were separate interfaces. debian way of configuring those: here.

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1 thing, if you're using solaris based traceroute, you can do a traceroute -I rtcamp.com which will use icmp for the traceroute. We do this at work since UDP traceroute is blocked on our Firewall.

The other thing, you may have an ACL on you're WAN router, or a Firewall not mentioned, that is blocking the icmp time-exceeded message. If you allow these messages, at least internally, traceroute should work (and there is no risk to allowing this, only some types of icmp messages are bad).

As for the clients not being able to talk to the servers, are they on the same subnet, or are they on a seperate, possible secured network that is non-routable? It sounds like a rather simple network, but it sounds like you're WAN router might be specialized, and not to actual routing internally???

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ICMP Unreachable packets are a special breed; they'll only be thrown back at your systems when a router cannot route for that destination, if the router's behaving correctly; you'll also need to make sure they aren't getting discarded by an overzealous firewall.

In the case of 10.0.0.1, the ISP is probably not filtering the RFC 1918 ranges out until hop 3 - but if the discard is due to an ACL filter, it'll just throw the packets away without sending an Unreachable response.

To get your linux router to drop the packets and throw unreachables, add a reject route:

route add -net 10.0.0.0 netmask 255.0.0.0 reject

You'll want to make this persistent - where you need to do this depends on your router's flavor of linux.

Best Answer

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