A smaller North American network provider, with a modest North American backbone, numbers their internal routers on public IP space that they do not announce to the world. One of the largest North American network providers filters/drops ICMP messages so that they only pass those with a source IP address that appears in their routing table. As a result, traceroutes from big.net into small.net have numerous hops that time out. Traceroutes from elsewhere that go into small.net but return on big.net also have numerous hops that time out. We do all still think that traceroute is important, don't we? If so, which of these two nets is unreasonable in their actions/policies? Please note that we're not talking about RFC1918 space, or reserved IP space of any kind. Also, think about the scenario where some failure happens leaving big.net with an incomplete routing table, thus breaking traceroute when it is perhaps most needed. Thanks, -mark