255.255.255.255 - as subnetmask

his original question was concerning PPP - if you are using PPPo[A/E] at home (e.g. DSL) check your connection and you will see you've been assigned a /32 host route. Its normal for PPP and its kinda cool because you can have routers on different subnets talk to each other over a Point to Point link.

Thanks, Never knew that before novembre!!. I just tried a dial-up connection and it indeed gave me a /32 mask. Not sure how this works though interms of ISP router IP. I could understand that the router has several /32 routes for each connection but what would be the router IP? or doesn't it need one? ipconfig shows the gateway IP to be the same as my IP!!.

Or does the router use a supernet mask? I hope I'm not out of scope here.

*Bows Head in Shame* I stand corrected. After a few hours of research, I guess it is also common for a ADSL provider to provide a /32 subnet as well. I read one article that implied that everything acts as a broadcast. Since ADSL uses spilt horizon, broadcast dont go back the way they came, it acts a P-to-P link.


Learn something new everyday on this forum!

As far as DSL providers assigning "/32" addresses, it is so that they don't have to assign 4 of their IPs to each client - obviously a wise business decision. This is not transparent on both sides, rather on the ISP's side, your interface is probably setup with a sticky IP in some DHCP pool with a /24 netmask. I suppose the biggest thing to understand here is that a client and a router do not need to have the same subnet mask... the client only needs to have a SN mask such that it's GW resides within its SN mask.

Since on a /32 network, all traffic acts as a broadcast, when received on the ISPs end, it is picked up and NAT ensues... I hope I haven't bee too vague.

I could understand that the router has several /32 routes for each connection but what would be the router IP? or doesn't it need one? ipconfig shows the gateway IP to be the same as my IP!!.

Or does the router use a supernet mask? I hope I'm not out of scope here.

I'm not to sure I follow your question, which router IP? CPE gateway or ISP edge?. Remember IP is encapsulated within PPP across the link. The ISP router will have a whole bunch of /32's but will advertise them within the network as an aggregate route, which is I guess is a type of supernet route but I think strictly speaking supernet refers a collection of classful networks. An aggregate route is a just a summary of whatever is convenient.

I'm not to sure I follow your question, which router IP? CPE gateway or ISP edge?.

I meant the ISP edge. i.e the far side of the link (at layer 3). But I guess if all traffic is considered broadcast, then the IP wont be needed. The thing is that I've never practically dealt with a two point layer 3 link that has less than two IPs. The /32 mask obviously allows only one IP

Remember IP is encapsulated within PPP across the link.

Sure.

The ISP router will have a whole bunch of /32's but will advertise them within the network as an aggregate route, which is I guess is a type of supernet route but I think strictly speaking supernet refers a collection of classful networks. An aggregate route is a just a summary of whatever is convenient.

One definition of a supernet is: "a block of contiguous subnetworks addressed as a single subnet". en.wikipedia.org/wiki/Supernet . Not that I always trust Wikipedia, but usually good.