03-01-2002 04:36 AM - edited 03-01-2019 08:41 PM
I am trying to figure out if I can use a cable modem with my Cisco 3600 series router? My cable modems IP address is dynamic so it can change on me. How can I configure my router to send traffic out a port that might change? I have 6 users on my network and want to implement this router to get practice with it. Any input would be helpful. Thank you.
03-01-2002 05:08 PM
I would think that you could install a "default" route to that interface. Ex.- if you connect to the cable modem via EO or S0 then, 0.0.0.0 E0 or 0.0.0.0 S0. Let me know what you find out. I want to do the same config. @ home.
03-02-2002 05:53 AM
You need to have an IOS with the DHCP client capability on it.
I use 12.2(6a) IP Plus feature set (c3620-ik9o3s-mz.122-6a.bin for VPN & firewall as well) and then configure my "internet" ethernet port with a MAC address that my cable company knows about and set it for DHCP.
I've enclosed a portion of my config so that you've got an idea. Good luck...
interface Ethernet0/1
mac-address xxxx.xxxx.xxxx
ip address dhcp
ip access-group 111 in
ip nat outside
no ip mroute-cache
half-duplex
no cdp enable
ip route 0.0.0.0 0.0.0.0 Ethernet0/1
03-03-2002 08:24 AM
I'm using a 1710 Security Access Router but the config will be very similiar to the 3600. I'll assume you have a 3620 w/ 2 ethernet ports one for inside LAN interface and one for the outside cable modem interface. Most cable providers will have limitations of 10mb half duplex on their access so you will need to use either auto or hard code the port for 10mb half (outside interface). My inside interface is a fastethernet port so I use a static config of 100mb full. Since you have a dynamic ip address for your outside interface you need to use "ip address dhcp" command for your e0 or whatever is your outside interface. I have also included an extended access list for inbound entry which includes access for dhcp ports to past to the outside interface. Below is a sample config, just apply your ip addresses internally and you should be set. Good luck.... jw
interface Ethernet0
ip address dhcp
ip access-group 101 in
ip nat outside
half-duplex
!
interface FastEthernet0
ip address 192.168.254.11 255.255.255.0
ip nat inside
speed 100
full-duplex
access-list 1 permit 192.168.254.0 0.0.0.255
access-list 101 permit tcp any any established
access-list 101 permit udp any eq domain any
access-list 101 permit tcp any any eq ftp
access-list 101 permit udp any eq bootps any eq bootps
access-list 101 permit udp any eq bootpc any eq bootpc
access-list 101 permit tcp any any eq ftp-data
03-19-2002 11:37 AM
Don't forget the access-list 101 deny any any statement at the end of your access list. Else all is for naught.
03-05-2002 07:08 PM
I've been following your discussion. I'd really like to know if you tried the default route like ccsn-cnap has pointed out.
It's a really easy concept and I don't see why I should'nt work.
Tell me if you get a chance. Thanks
Dave
03-08-2002 11:01 AM
Actually, both must be implemented.
For Layer 3 connectivity, the router needs an IOS image that supports DHCP (and any other features you require).
Set the public Fa0/0 to use DHCP (you may also need to use the physical-address command to modify your MAC address on that interface).
Be sure to modify any ACLs to permit BOOTP in and out (client and server).
Then for Layer 3 ROUTING purposes, set a default route out to the FA0/0 interface.
Copy run start, power it all off for 60s, and then bring up your DSL modem, then 60s later the router.
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