[ipxe-devel] Subnet mask 255.255.255.255 doesn't work

[Michael Brown]

On 26/06/15 18:55, Josh Jameson wrote:
> I am having an issue where I need to provide /32 DHCP request where the
> gateway is outside the subnet.
>
> For example consider the following DHCP offer;
>   IP: 10.0.0.50
>   Netmask: 255.255.255.255
>   Gateway: 10.1.0.1
>
> iPXE doesn't seem to communicate right. It times out when trying to get
> a HTTP request at http://10.1.0.1/.

That doesn't surprise me.  By specifying a subnet mask of 
255.255.255.255, you are telling iPXE (or any other client) that there 
is one and only one IP address on that network, which is the 10.0.0.50 
address itself.  You have not provided any way for the client to reach 
10.1.0.1.

>If I boot the same machine and
> network config into Linux or Windows I can access the URL.

That _does_ surprise me.  I tested it just now: as expected, Linux fails 
to communicate with 10.1.0.1.  (Specifically, it refuses to even add 
10.1.0.1 as the default gateway, since that address is not within the 
designated local network range of 10.0.0.50-10.0.0.50).

I'm not sure what network topology you're actually trying to create.  Is 
the iPXE client in the same broadcast domain as the gateway (i.e. if you 
send a broadcast such as an ARP request from the iPXE node, do you 
expect it to reach the gateway)?  If so, then you are probably using a 
subnet mask of 255.0.0.0.

See https://en.wikipedia.org/wiki/Subnetwork#IPv4_subnetting for some 
basic introduction to subnet masks.

Hope that helps!

Michael