External DHCP server with Linux or Win2008 work? 2

[dvtestguy]

I normally use Cisco DHCP Pools for DHCP Clients, but was told we're moving to extrnal DHCP servers yet TBD.

Any TT members have working examples of either Linux or Win2008? The only catch in my environment is i need to use Vlan ranges as i did with the DHCP Pools.

I'd like to see if anyone has had success with either platform or what cisco cofigs have worked best.

Here's what I'm chaging from...

ip dhcp pool vlan600
network 10.115.60.0 255.255.255.240
default-router 10.115.60.1
lease 10
!
interface GigabitEthernet5/0.600
encapsulation dot1Q 600
ip address 10.115.60.1 255.255.255.240
ip access-group 100 in
ip nat inside
no cdp enable


Thanks all!

 

[Quadratic]

Migrating this should be fairly straight forward. Just remove the DHCP pools, and add an "ip helper-address" command pointing each subinterface to the intended DHCP server.

CCNP, CCDP

 

[dvtestguy]

Quadratic...

Considering my new router IP interface = 10.77.50.1, what happens to the existing default-router 10.115.60.1 IP in the DHCP Pool? My undertsnading was that you also needed a gi-address = the default-router 10.115.60.1?

 

[chieftan]

I think Quadratic is trying to tell you that you may be utilising an external DHCP server.

This means you no longer have a requirement for a pool on the Router nor a default-router command, but instead a helper address (Relay agent) as DHCP requests are broadcast and we all know layer three devices do not forward broadcasts.

So, you may end up with something like:-

interface GigabitEthernet5/0.600
encapsulation dot1Q 600
ip address 10.115.60.1 255.255.255.240
ip helper-address xxx.xxx.xxx.xxx
ip access-group 100 in
ip nat inside
no cdp enable

Doing this from memory so please excuse if the command is not exact.....

 

[Quadratic]

The "default gateway" is assigned to the host by the DHCP server. You say that you're "moving to external DHCP servers", so you're router will have less responsibility. Instead of handling the pools or assigning any DHCP options (default gateway, among others), you just point the DHCP discovers and requests to the new DHCP server with the "ip helper-address x.x.x.x" command.

CCNP, CCDP

 

[dvtestguy]

Quadrac,

...on my linux server, i've configured dhcp for the following uisng eth1 and vlan 500 as a starting point for proof of concept.

#Cisco router:
interface GigabitEthernet5/0.600
encapsulation dot1Q 600
ip address 10.115.60.1 255.255.255.240
ip helper-address 10.115.50.1

#cat /etc/dhcp3/dhcp3-server
subnet 10.115.50.0 netmask 255.255.255.0 {
range 10.115.50.2 10.115.50.14;
option broadcast-address 10.115.50.255;
option routers 10.115.50.1;

#cat/etc/network/interfaces:
auto eth1
iface eth1 inet static
address 10.77.50.3
netmask 255.255.255.0
broadcast 10.77.50.255
#gateway 10.77.50.3
up route add -net 10.77.50.0 netmask 255.255.255.0 gw 10.77.50.3 dev eth1

auto eth1.500
iface eth1.500 inet static
VLAN 500
address 10.115.50.1
netmask 255.255.255.0
network 10.115.50.0
broadcast 10.115.50.0
vlan_raw_device eth1

 

[chieftan]

I think you may have the option router statement wrong in the following:-

(Are you using Debian??? or Ubuntu???)

#cat /etc/dhcp3/dhcp3-server
subnet 10.115.50.0 netmask 255.255.255.0 {
range 10.115.50.2 10.115.50.14;
option broadcast-address 10.115.50.255;
option routers 10.115.50.1;

Anyway, the option router statement is surely assigning the GW to the clients?
If this is the case you are assigning the DHCP server address as the GW for the clients. Surely you want the Cisco Router interface for the LAN as the GW for the clients?

 

[Quadratic]

I think this question is dipping into the Linux/sysadmin world. The configuration of the router should just involve removing the pools and defining IP Helpers to relay the DHCP traffic, but if you're looking to correct your Linux config files I think this might get a better answer in the Linux boards.

CCNP, CCDP