Read IPv4 and client tools.
DHCP leases and client configuration options
DHCP can supply an IPv4 address, mask, default gateway and DNS settings for a lease period. A common initial exchange is Discover, Offer, Request and Acknowledge. The server needs a suitable pool and must avoid handing out infrastructure addresses already in use.
A router normally does not forward a client’s local broadcast to another subnet. A DHCP relay can send the request toward a server elsewhere. On Cisco IOS, configure ip helper-address on the client-facing Layer 3 interface. Routing in both directions and a server pool for the client subnet are still required.
DNS queries and resource records
DNS stores many kinds of records. A records represent IPv4 addresses; AAAA records represent IPv6 addresses. A resolver may cache an answer according to its time to live. A domain name can have more than one address, and the answer can change. DNS does not itself carry a web page or allocate a client address.
Test IP reachability and DNS separately. A DHCP lease with the wrong DNS server can allow ping by IP while name lookups fail. A valid DNS answer does not prove that a firewall permits the application or that the server is healthy.
Verification commands
Use these viewing commands to inspect the idea in this lesson. Start in the environment shown above each example.
show ip dhcp bindingCommand reference · enter in the stated environment; output varies by device.
Practical exercise
A remote DHCP server is reachable from the router, but clients get no leases. Where should the relay setting normally be placed?
Show the answer and explanation
On the Layer 3 interface receiving the clients’ broadcasts, such as their router interface or SVI. Also inspect the pool, relay address, filters and return route.
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Technical references checked on 25 October 2026. These are original teaching explanations, not official Cisco course material. See how content and lab validation are described.
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