Hi, I have an external NIC on my isa server that has 5 additional ip addresses added to it in the advanced section of tcpip settings. addresses are 202.xx.xxx.xx with a subnet mask of 255.255.255.248 Everything is working fine.I need to add additional public ip addresses as a web server sits behind isa. Problem is when i add the 6th ip address with the above subnet mask I get error message The combination of ip address and subnet mask is invalid. All of the bits in the host address portion of the ip address are set to 0. Please enter a valid combination of ip address and subnet mask. This machine is virtual (hyper v)Thanks in advance

You receive the error, becausewith a 255.255.255.248 subnet you can use a block ofsix addresses. The 255.255.255.248 subnet mask marks 29bits of the 32bits of an IP address as the network portion.For instance when you have the 202.0.0.0/29 range you can use the 202.0.0.1 to 202.0.0.6 addresses.When looking at the lastthree bits of the IP addresses you''ll see the addresses corresponding with the address range are:202.0.0.0 11001010 00000000 00000000 00000000202.0.0.111001010 00000000 00000000 00000001202.0.0.211001010 00000000 00000000 00000010202.0.0.311001010 00000000 00000000 00000011202.0.0.411001010 00000000 00000000 00000100202.0.0.511001010 00000000 00000000 00000101202.0.0.611001010 00000000 00000000 00000110202.0.0.711001010 00000000 00000000 00000111Red text is the network portion. Green text the host portion.Host portion consisting of all zeros (in this case 000) is the network address. It cannot be assigned to a Windows host.Host portion consisting of all ones (in this case 111) is the broadcast address. It can also not be assigned to a host. In your case you tried to assign an address where the host portion contains all zeros. Windows does not recognize this address as a valid address.

Thanks for the informative answer.what do i need to do to be able to have say 20 public ip addresses on this nic?

If you want to use 20 IP addresses you will need to contact your Internet Service Provider (ISP). Ask them to provide you with a network, using at least a27 bit(255.255.255.224) subnetmask. This will allow you to host services from 30 usable IP addresses. Note: Since ISPs often serve many customers and share out many subnets you may not end up with an extension of your current subnet. You may need to change the entire range of IP addresses in use. Note:Your ISP will probably charge you a surplus. IPv4 addresses are no longer considered a commodity.