Using Class to have ip address on unknown network segments

[Niall O'Reilly]

At Thu, 19 Feb 2015 16:39:39 -1000,
Teva A-T wrote:
> 
> I'm trying to use class to provide ip address to LTE customers which
> is on a network segment unknown by the dhcpd server.

  Stop trying.  It can't work.

> Here below what i can see when my LTE customers is sending its DHCP
> Discover : 
> 
> dhcpd: DHCPDISCOVER from 50:00:00:00:00:04 via 10.9.0.4: unknown
> network segment
> 
> So indeed, 10.9.0.0 is not a network segment known by the dhcpd.
> 10.9.0.4 is just a relay agent,

  It's rather more than "just a relay agent". This is the GIADDR field
  of the DHCP message, set by the relay agent to identify the network
  segment where the client is connected.

  In other words, the relayed request means, "please give an address
  for a client on THIS network."

  Part of the DHCP server configuration ('shared-network' and 'subnet'
  sections) models the network topology.  The server uses GIADDR to
  identify which part of this model is the one from which an address
  for the client must be assigned.

> and what i want is to provide to my
> LTE cust an ip in subnet 172.16.192.0/19. For that, i thought that i
> could use class, and then allow members of this class to get an ip,
> even if the network segment is unknown.

  You can use class to select the subnet, but you need a different
  approach.

  The GIADDR value presented by the relay must belong to a known
  subnet. This may be either the same subnet as is intended for
  clients, or another one on the same shared network.

  It seems you will need to add a subnet to the shared-network
  definition you alrady have, so:

shared-network lte-cust {

option domain-name-servers 1.1.1.1,2.2.2.2;
default-lease-time 360;
max-lease-time 360;

subnet 172.16.192.0 netmask 255.255.224.0 {
option routers 172.16.192.254;
option subnet-mask 255.255.224.0;
option broadcast-address 172.16.255.255;
}

subnet 10.9.0.4 netmask 255.255.255.255 {
    # minimal (/32) subnet for relay
    # you may need a shorter prefix
}

pool {
allow members of "lte";
range 172.16.192.1 172.16.192.255;
}

}

  I've just seen that Simon Hobson got to press 'Send' while I was
  still typing.  As usual, his advice is excellent. Since there are
  one or two differences in both detail emphasis between his advice
  and mine, I may as well send anyway ...

  Best regards,
  Niall O'Reilly