On Fri May 05/30/03, 2003 at 11:43:32AM -0600, Scott Mecham wrote: > Need help with subnetting. > > My company owns a half of a class C license of ip's. For example I'll > call the network 10.5.73.0/24. But we are only allocated the upper > portion of the class C ip range (10.5.73.128-10.5.73.255). > > How do I mask these out to my router and then to my firewall? How do I > mask out only the upper part of the ip range? > > I've tried 10.5.73.128/25 or 255.255.255.128. But it does not work properly. > > We have a T1 internet line. Then a Router. Then a firewall wich provides > NAT. Then our LAN (192.168.0.0/24).
What kind of router? If Cisco, what IOS version? http://www.cisco.com/en/US/partner/tech/tk648/tk361/technologies_tech_note09186a0080093f18.shtml#theallonesubnet (beware of line wrap, and you might need a CCO login to see that URL). Cisco IOS since 12.0 should be able to utilize the all-1's subnet of 10.5.73.128/25. I know for a fact that OpenBSD can utilize that type of subnet address, and I expect that other modern *nix hosts will not have configuration issues with that subnet address (I've just never tested it myself). If the router is a Cisco post-12.0, or a *nix host, please define "does not work properly." ;) -- Greg White
