From owner-lir-wg@ripe.net Thu Jul 11 23:01:33 1996 From: Daniel Karrenberg <Daniel.Karrenberg@ripe.net>

Daniel,

Also note that even for private address space traceroute will return the address correctly, so the diagnostics are useful. There just are no names. If the border gateways with publicly adressed interfaces has a reasonable name such as 'bordergw-xxx.clever.net' 'clever-gw.customer.nl' it is quite clear "where you are" in between.

Although I agree in general with your statement above, I think the details are not necessarily true. According to RFC 1918: Because private addresses have no global meaning, routing information about private networks shall not be propagated on inter-enterprise links, and packets with private source or destination addresses ^^^^^^^^^^^^^^^^^^^^^^^^^^^ should not be forwarded across such links. Routers in networks not ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ using private address space, especially those of Internet service providers, are expected to be configured to reject (filter out) routing information about private networks. If such a router receives such information the rejection shall not be treated as a routing protocol error. If an ISP is taking this recommendation by the letter, then they install a filter on the border routers to filter out these packets (as we do ourselves). In this case though, a traceroute from outside will not receive any packets from the interfaces that have a IP address from the private addresse space. I agree however that the answers from the other routers will give you in most of the cases enough information to figure out what route the packets take. Regards, Janos