Today I was lucky to work and had to add and additional IP range to an Fiber connection of a dutch ISP ( KPN )
And the company where I was working got an extra ip range on their fiber connection. the IPS redirect that ip range to your own router connect. which i configure most of the time as bridge first before we add an other device behind it.
start with the DHCP configuration
ip dhcp use vrf connected ! ip dhcp pool IAS import all origin ipcp dns-server < dns server 1 > <dns server 2> ! ! no ip domain lookup ip name-server <dns server 1> ip name-server <dns server 2>
Then the connection of the internet
interface FastEthernet0/0 description Link to EVPN CPE no ip address load-interval 30 speed 100 full-duplex pppoe enable group global pppoe-client dial-pool-number 10
interface Vlan1 ip address pool IAS ip access-group 99 out ip verify unicast reverse-path ip tcp adjust-mss 1452 load-interval 30
Configure a Dialer interface
interface Dialer10 description Customer Traffic PPPoE Connection mtu 1492 ip address negotiated ip verify unicast reverse-path encapsulation ppp dialer pool 10 dialer-group 10 no cdp enable ppp pap sent-username <username> password <username> ppp ipcp mask request ppp ipcp address accept
You will need to add a router for general use the 0.0.0.0 and the extra ip range.
ip route 0.0.0.0 0.0.0.0 Dialer10 ip route <extra ip range> <extra ip range subnet> Vlan1
When you have add this extra ip range you can use the new range to an old or new device. the gateway for that device will be the old IP range
Download here a sample configuration