• We’re currently investigating an issue related to the forum theme and styling that is impacting page layout and visual formatting. The problem has been identified, and we are actively working on a resolution. There is no impact to user data or functionality, this is strictly a front-end display issue. We’ll post an update once the fix has been deployed. Thanks for your patience while we get this sorted.

Cisco 1721 + DHCP question

D

dailow

Member
Question for you Cisco people here:

I have a Cisco 1721 router sitting at home, which I'm planning to use for my ADSL connection. It has one FastEthernet interface, and an Ethernet WIC. The Fa0 interface is connecting to an external ADSL modem, and the E0 interface is facing my LAN.

I get my WAN IP via DHCP, and that's fine. What I want to be able to do is pass some of the WAN settings learned via DHCP to clients on the LAN via DHCP, and that's where I'm stumbling around. I realize this is something pretty much all consumer routers do, I just haven't figured out the IOS commands to do the same. Configuring DHCP for LAN clients is straight forward enough, but I'm not sure if there is a way to pass on the DNS server information learned from the WAN, onto the LAN.

Then again, this wouldn't be an issue I could get the Cisco router to do the DNS lookups. It seems the name-servers you specify in global config are only local to the Cisco router. I found that if my LAN clients used the Cisco router IP for DNS, it didn't go anywhere - I was still able to browse and ping on the Internet via IP though. I tried adding helper addresses, but that didn't seem to help so I kinda gave up on that.

Anyone have any ideas?
 
I saw that upon some brief Googling, but not what I'm looking for... his DHCP configuration for the LAN has the hard coded DNS servers. What I want to do is dynamically take the DNS servers learned from DHCP on the WAN, and pass those on to the DHCP clients on the LAN.
 
Well, assuming that the DNS servers on your ISP's network will communicate DHCP with your LAN, the IOS command is:

conf t
int ethe 0
ip helper-address [dhcp server ip addy]

By default your cisco router is going to drop dhcp requests at a subnet boundary. This command allows the router to pass dhcp through the subnet to your local clients. Configure the helper address on the interface closest to your clients.
 
You must log in or register to reply here.

TRENDING THREADS

Back
Top