Posted 19 June 2011 - 05:50 PM
Your biggest concern appears well founded. It's certainly not best practice for an ISP to directly bridge clients together, although it often happened that way in the early days of Cable Modems. DSL has usually been 'smarter' than that. Your DSL provider may have an option in the DSLAM for subscriber isolation, which at least prevents them from directly contacting one another, but it sounds like they are not even using that. From the ISP's point of view bridging clients can be a disaster too. Just plug the DSL modem ethernet into one of the shared LAN ports on a home router and let it hand out DHCP addresses to all of their clients for a few hours and I bet you get their attention. I work with a couple of ISP's and we have a hard rule, either you have a router (which we will give a public IP to if needed) or we configure our unit as a NAT router for your (and our) protection. Under no circumstances may a client PC connect directly to the net. Certain addresses (RFC1918, loopbacks, directed broadcasts, etc.) and protocols (notably Netbios) are blocked at the edge as well, if the equipment is capable. These are basic protections for the ISP as well as the client.