Cisco 2600 Router and a dynamic IP from a Cable Modem

[comdata55]

Question 1: I'm new to Cisco hardware. I'm trying to set up a Cisco 2600 router to a cable modem from Optimum Online. I do not have a static IP address with this account. How can I get the router to obtain the IP assigned by my ISP?

 

[labgrl76]

Hey, I had this same issue in dealing with Comcast highspeed since they won't allow you to use static IP. This setup uses dhcp to grab an ip from your incoming (internet) and provides NAT to your internal network connection. Now since I don't have a DHCP server on my internal network I have the router do it which seems to work just fine. I am assuming you have 2 ethernet interfaces on your 2600 series. BTW on the internal side I've chosen to use an exclude command which tells the routers DHCP server to excluded addresses 10.0.100.1-99 and begin issuing addresses at 10.0.100.100 and so on. This setup seems to work well with no issues. Good luck.

hostname 2514
!
boot-start-marker
boot-end-marker
!
enable secret 5 xxxxxxxxxxxxxx
enable password xxxx
no aaa new-model
ip subnet-zero
no ip source-route
ip cef
no ip domain lookup
no ip dhcp conflict logging
ip dhcp excluded-address 10.0.100.1 10.0.100.99
!
ip dhcp pool internal
network 10.0.100.0 255.255.255.0
default-router 10.0.100.1
dns-server 64.87.64.146 68.87.75.194
netbios-name-server 10.0.100.2 10.0.100.3
lease 5
!
no ip bootp server
!
!
!
interface Ethernet0
description DMZ
ip address dhcp
no ip unreachables
no ip proxy-arp
ip nat outside
no cdp enable
!
interface Ethernet1
description INTERNAL
ip address 10.0.100.1 255.255.255.0
no ip proxy-arp
ip nat inside
no ip route-cache
no cdp enable
!
interface Serial0
no ip address
shutdown
no fair-queue
no cdp enable
!
interface Serial1
no ip address
shutdown
no fair-queue
!
ip nat inside source list 1 interface Ethernet0 overload
no ip http server
ip classless
!
!
access-list 1 permit 10.0.100.0 0.0.0.255
!
!
line con 0
exec-timeout 0 0
password xxxxxxx
logging synchronous
login
line aux 0
line vty 0 4
access-class 1 in
password xxxxxxx
login
!
!
end

 

[labgrl76]

Just a quick note, not trying to insult, but just incase you're not sure where the "dns-server" command is in that config file above take mine out and simply plug your provider's dns numbers in place of it.