Subnet mask 255.255.255.255

I was just at a friends place and happened to look at ipconfig.. his ISP gives him a dynamic IP, but what was wierd was the subnet mask was 255.255.255.255

Wouldn't this logically mean only one host per subnet and a total of 255 subnets. Why would anyone want to do this ?

I'm not sure why this would be used outside of a routing table. I think DHCP uses it also.

It means single host address and is used in a routing table to mean all the bits must match (only one host). 0.0.0.0 means a gateway address in a routing table.

Yep 10/10 about its use in the routing table, i just cant fathom why it would be used for a particular host. Its not a misconfiguration as I just spoke to someone else on the same ISP and he has the same mask. Not to mention the connection works fine.

Its probably something normal, Chris has probably seen it before, i was wondering because the ISPs here in India do some wierd things with their networks.. its almost like an alternative networking world here.. you should come and have a look . Half the time when their networks go down I think they just sit back and pray, hoping that they'll come back up. We have some damn fine network engineers and some absolute twits. I guess its the same everywhere though

Cheers

Do a google search on 255.255.255.255?

There is quite a bit on it. One of the pages might have something on it.

Sahir,

Your friend must be on a dialup connection to his ISP.

It's common for all dialups to have a subnetmask of 255.255.255.255. As TFS noted, its used to specify one IP address without assining it to a network.

The person dialing up creates his on "stub" network to his ISP.
When he connects to the Internet, his IP address is also his broadcast address and network address (from the user's perspective), while the ISP maintains their own routing tables in order to allow packets to reach the dialup user.

Dialup connection it is
But what would be the advantage of this ? wouldn't it just make for a vey large routing table for them ?