Remember, SOHO devices are configured as DHCP clients by default. When you are DHCP client to your ISP you need to configure interface on enterprise device to receive IP address.
I have created topology as it is shown in Slide 1.
ISP router is configured as DHCP for 192.168.100.0/24 network with 192.168.100.1 on Fa0/0.
On ISP_Client router you need to enable Fa0/0 to be DHCP client. Please, configure your router as follows:
ISP_Client(config-if)#ip address dhcp
First verify that you recieved IP address with show ip interface brief. My output looks like this:
ISP_Client#show ip interface brief
Interface IP-Address OK? Method Status Protocol
FastEthernet0/0 192.168.100.2 YES DHCP up up
FastEthernet1/0 unassigned YES unset administratively down down
FastEthernet1/1 unassigned YES unset administratively down down
GigabitEthernet2/0 unassigned YES unset administratively down down
Notice that we have IP address on FastEthernet0/0. Now verify your routing table with show ip route:
ISP_Client#show ip route
Codes: L – local, C – connected, S – static, R – RIP, M – mobile, B – BGP
D – EIGRP, EX – EIGRP external, O – OSPF, IA – OSPF inter area
N1 – OSPF NSSA external type 1, N2 – OSPF NSSA external type 2
E1 – OSPF external type 1, E2 – OSPF external type 2
i – IS-IS, su – IS-IS summary, L1 – IS-IS level-1, L2 – IS-IS level-2
ia – IS-IS inter area, * – candidate default, U – per-user static route
o – ODR, P – periodic downloaded static route, H – NHRP, l – LISP
+ – replicated route, % – next hop override
Gateway of last resort is 192.168.100.1 to network 0.0.0.0
S* 0.0.0.0/0 [254/0] via 192.168.100.1
192.168.100.0/24 is variably subnetted, 2 subnets, 2 masks
C 192.168.100.0/24 is directly connected, FastEthernet0/0
L 192.168.100.3/32 is directly connected, FastEthernet0/0
Along with IP address you will “receive” default route to your ISP.