DHCP server behing Cisco relay

Patrick Trapp ptrapp at nex-tech.com
Fri May 20 21:54:37 UTC 2016


Also, if you are intending for addresses to be made available from both of the subnets, I believe you may need to define those pools as a shared network. Look up shared-network in your handy DHCP documentation, but I would wonder if something like this would make a difference:

default lease-time 600;
max-lease-time 7200;

shared-network Combined-pools {
subnet 10.0.0.0 netmask 255.255.0.0 {
  range 10.0.0.10 10.0.200.200;
  option subnet-mask 255.255.0.0;
  option routers 10.0.0.1;

option domain-name-servers 8.8.8.8, 8.8.4.4;
}

subnet 192.168.120.0 netmask 255.255.255.0 {
}

}

Or, so be more generic

shared-network shared-network-label
{
subnet1 x.x.x.x netmask 255.x.x.x
{
} (to close subnet1)
subnet2 y.y.y.y netmask 255.y.y.y
{
} (to close subnet2)
} (to close the shared-network declaration)

________________________________
From: dhcp-users-bounces at lists.isc.org [dhcp-users-bounces at lists.isc.org] on behalf of José Queiroz [zekkerj at gmail.com]
Sent: Friday, May 20, 2016 4:46 PM
To: Users of ISC DHCP
Subject: Re: DHCP server behing Cisco relay

Hi Hernan,

Could you please post the Cisco Switch's relevant configuration, also? Including the VLAN interfaces serving the 10.0.0.0/16<http://10.0.0.0/16> network.

By the way, does this switch have conectivity with your dhcp server? This is mandatory for the DHCP relay to work, as the relay agent needs to forward DHCP messages for clients in unicast to the DHCP server; and the reverse path must be available also, once you're checking the direct path, give some time checking this also.


2016-05-20 17:58 GMT-03:00 Hernan Saltiel <hsaltiel at gmail.com<mailto:hsaltiel at gmail.com>>:
Hi everybody.

Maybe I'm asking something previously answered.
I configured my new iscp-dhcp-server (Ubuntu 16.04) to server requests from a network of APs.
Those APs are connected to a Cisco switch, having 192.168.120.1/24<http://192.168.120.1/24> as primary address, and a secondary subnet with address 10.0.0.1/16<http://10.0.0.1/16> (yes, 16...). It has relay configured, just to send the dhcp requests to 192.168.120.20, a Windows machine.
Today I have a Windows machine connected there, where I use the AP controller software, and TFTPD64, a thin software that works as a DHCP server. I configured there a range (10.0.0.10 -> 10.0.200.200) and everything works well, but it's Windows, then from time to time, I have to reboot the system.
This is why I configured the new machine as 192.168.120.40/24<http://192.168.120.40/24>, installed isc-dhcp-server package, and configured the following lines on /etc/dhcp/dhcpd.conf:

default lease-time 600;
max-lease-time 7200;

subnet 10.0.0.0 netmask 255.255.0.0 {
  range 10.0.0.10 10.0.200.200;
  option subnet-mask 255.255.0.0;
  option routers 10.0.0.1;
  option domain-name-servers 8.8.8.8, 8.8.4.4;
}

subnet 192.168.120.0 netmask 255.255.255.0 {
}

When I start the server, I only see it trying to answer requests using network 192.168.120.0, then saying "no free leases", and not serving any 10.0.0.0/16<http://10.0.0.0/16> address.

Now I'm living with TFTPD64, but I plan to move that to a better solution.
Does anybody know about this configuration? Is there something I'm doing wrong?
Thanks a lot in advance, and best regards.

--
HeCSa

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