Re: Question about adding a logical network

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Antonio Varni wrote:

>I'm trying to add a second logical network to our current physical
>network (because we're running out of IPs during high usage times lately).
>The full network is 192.168.2, the new one is 192.168.4:
>
>shared-network DHCP {
>    authoritative;
>    subnet 192.168.2.0 netmask 255.255.255.0 {
>            authoritative;
>            range 192.168.2.64 192.168.2.254;
>            default-lease-time 900;
>            max-lease-time 3600;
>            option routers 192.168.2.1;
>    }
>
>    subnet 192.168.4.0 netmask 255.255.255.0 {
>            authoritative;
>            range 192.168.4.10 192.168.4.254;
>            default-lease-time 900;
>            max-lease-time 3600;
>            option routers 192.168.4.1;
>    }
>}
>
>
>In order to test this out immediately -- I'm trying to artificially
>shrink our current full network by decreasing the range by about 30 ips,
>
>so from the above this:
>range 192.168.2.64 192.168.2.254;
>becomes this:
>range 192.168.2.64 192.168.2.200;
>
>I was expecting that when a DHCPREQUEST came in from a client
>in the newly invalidated range -- the dhcp server would assign
>it a new ip.
>. . . Problem is that when a DHCPREQUEST comes in from a client
>say at 192.168.2.210 -- the dhcp server ignores the request.
>
>I'm off to go read the RFCs again -- if anyone can shed some light on
>this for be -- TIA :)

Simple. Client has an existing lease with time unexpired on it, the 
lease is still valid for the subnet (even though it is no longer in a 
range), therefore the server will not DHCP-NAK it. The client will 
keep trying, and eventually (as the lease time runs out) "go back to 
the beginning" and make a DHCP-Discover request, at which point the 
server will assign it a new address.

If you NEED to terminate leases in the deleted range, then you can do this :

pool {
   range 192.168.2.64 192.168.2.200;
}
pool {
   range 192.168.2.201 192.168.2.254;
   deny booting ;
}

Then next time the client tries to renew, the server will see that 
it's address is now denied for use, and will reply with DHCP Nak. 
Note that this only happens when the client attempts to renew the 
lease, you CANNOT force it to happen sooner from the server side.


Then Paine, Thomas Asa wrote:

>       I'm not sure if this the case, but if you are relaying the
>requests through a router interface it may only be relaying based on one
>of the subnets.  A Cisco router interface with a secondary IP address
>only relays based on the first address, sooo another case might be there
>are no requests coming from your second logical 192.168.4.0/x network.
>It would not send two unicast packets onto the DHCP server.  Hope this
>helps.

It does NOT matter what interface address the relay agent uses, the 
server knows that the two subnets are on the one physical interface 
because they are in the shared subnet declaration, that is the 
function of the shared network statement !

Simon

-- 
Simon Hobson, Technical Services Engineer
Colony Gift Corporation Limited
Lindal in Furness, Ulverston, Cumbria, LA12 0LD
Tel 01229 461100, Fax 01229 461101

Registered in England No. 1499611
Regd. Office : 100 New Bridge Street, London, EC4V 6JA.

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