Handing out DHCP on two interfaces

[sz_danii]

This is my first post so go easy on this "stupid-question alert" one :) 


I have a router setup behind an ISP router. My router gets a DHCP address on this side fine, is NAT'ed fine and if I attach a PC it is handing out it's own IPs from it's DHCP pool as expected. This is on e1/0:

ip dhcp excluded-address 192.168.0.1 192.168.0.50
!
ip dhcp pool CTXHDXLAB
network 192.168.0.0 255.255.255.0
default-router 192.168.0.1
dns-server 8.8.8.8
!

!
interface Ethernet1/0
ip address 192.168.0.1 255.255.255.0
ip nat inside
ip virtual-reassembly in
!

I also need the router to hand out same for other interfaces like e1/1 but no matter what I do it doesn't work: 

interface Ethernet1/1
ip address 192.168.0.2 255.255.255.0
!

Surely I am missing the point here... please help me. 

[Seb Rupik · Accepted solution]

Hi there,

You cannot have two routed interfaces in the same VRF on the same router configured with IP addresses in the same subnet.

You have two options. 

* Add a switch to E1/0 to extend the broadcast domain.

* Create a BVI to bridge the two physical interfaces.

https://www.cisco.com/c/en/us/support/docs/lan-switching/integrated-routing-bridging-irb/200650-Understanding-Bridge-Virtual-Interface.html

cheers,

Seb.

[sz_danii]

That makes perfect sense now. So I have added a switch to e1/0 and aggregated it with another switch. Now I in a router-on-a-stick kind of scenario. 

How would you protect against failure of switch IOU1 here: 

[Seb Rupik]

If you are just using Layer2 switches, then I would opt for the BVI on the router to remove IOU2 dependency on IOU1.

If your router supports SVI's then you could configure the interfaces as switchports, connect each switch directly to router and trunk the relevant VLAN down to the switch.

cheers,

Seb.