Hi nanog, When we build MAN (Metropolitan Area Network), we're basically enable the ip layer communication between millions of end system - taking into account the number of family, business building PCs,etc. Recall the scarcity of IPv4 address, I wonder how this huge ip address demand was met in US ? In my mind, we have the following choices: 1. Build the MAN into a private address network, a class A network 10.x.x.x will be sufficient for most metropolitan. But the cons is: need PAT/NAT to access public Internet, and that leads to the potential performance bottleneck. 2. Just wondering, can we use a distributed DHCP system? In this scenario, we can almost convert the address consuming MAN into a 10 to 1 (or 20 to 1) address pool, which achieve nearly the same address utilization efficiency of dialup address pool. Cons: don't know the scalability of DHCP, any comments? 3. Build the MAN into a IPv6 network, and use address conversion at the interconnection point between v4 and v6. Just an idea, feeling that conversion efficiency between v4-v6 should be better than NAT/PAT, any support comments? thanks ! Yu Ning -------------------------------------- (Mr.) Yu Ning, Chief Eng. Internet Network Product Dep. Data Com. Bureau, China Telecom Beijing, P.R.C. +86-10-62072357/54 --------------------------------------