Router on a Stick

[chris-abs1]

im trying to connect my DHCP Server to the clients, I'm a beginner and followed someyoutuve turtorials but with no luck

I have made two sub-interfaces and used ip-helper in my router and encap( the ip helper matches the DHCP server ip too) yet clients are still not getting address from the DHCP, how can i fix it? here is my show run:

Router#show run
Building configuration...

Current configuration : 593 bytes
!
version 12.4
no service password-encryption
!
hostname Router
!
!
!
!
!
ip ssh version 1
!
!
interface FastEthernet0/0
 no ip address
 duplex auto
 speed auto
!
interface FastEthernet0/0.2
 encapsulation dot1Q 2
 ip address 152.31.1.30 255.255.255.0
 ip helper-address 152.31.3.100
!
interface FastEthernet0/0.3
 encapsulation dot1Q 3
 ip address 152.31.2.30 255.255.255.0
 ip helper-address 152.31.3.100
!
interface FastEthernet0/1
 no ip address
 duplex auto
 speed auto
 shutdown
!
interface Vlan1
 no ip address
 shutdown
!
ip classless
!
!
!
!
!
line con 0
line vty 0 4
 login
!
!
end

[Mike P]

Chris,

I am not seeing any routing (static or dynamic) configured here.  Your router currently only knows how to get to the 152.31.1.0/24 and 152.31.2.0/24 networks because they are directly connected.  Where does your DHCP server reside in relation to your router?

v/r

Mike

[chris-abs1]

Thanks mike for the reply

it is connected to the same multilayer switch  the router is connected to. and on the default vlan

[Jon Marshall]

Okay then you need another subinterface on your router to route to that subnet on your L3 switch.

You can either add the vlan for the 152.31.3.0/24 subnet or create a new subnet just for routing, up to you but either way your router needs to be able to reach that IP subnet.

But if it is a L3 switch why are you using subinterfaces on the router.

You could simply create the SVIs on the L3 switch for the vlans and route there.

Unless this is a learning exercise ?

Jon

[chris-abs1]

also had trouble with that :( i kept getting an error message when trying ip-helper in the switch

after creating the vlans and and assigning them ip address then type:

int vlan x 

ip helper-address xxxxx

result :% Invalid input detected at '^' marker. (pointing to p in 'helper')

[Jon Marshall]

What is the model of switch ?

If you can't get that working then you need to use another subinteface on the router.

Jon

[chris-abs1]

3560 - 24ps

[Richard Burts]

I think that we are assuming that routing is enabled on the layer 3 switch. But if that is true then why do you need router on a stick? Can the original poster provide some clarification about this?

The fundamental problem here is that the router has helper address of 152.31.3.100 but has no route for that destination. There are several ways this problem can be solved:

- add another sub interface on the router interface for the 152.31.3 subnet (and make sure that the switch port to which the router connects is configured as a trunk port and that all three plans are permitted in the trunk)

- add a route on the router for that subnet (or at least for that host route) with a next hop in one of the plans that do connect to the router.

HTH

Rick-

[Jon Marshall]

Rick

I think that we are assuming that routing is enabled on the layer 3 switch.

You might be, I'm not :-)

Jon