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mediumservices~45 min

One subnet leases, the other stays dark

Two client subnets, one central DHCP server, one router relaying for them. One subnet gets addresses, the other gets nothing. Relay both.

Scenario

One central DHCP server hands out addresses for two remote client subnets, both a router-hop away. The router already relays one of them, so its clients lease fine. The other subnet leases nothing. Its clients sit there with no address.

You're handed the router and server configs. Interfaces are up and the router can reach the server. Get both client subnets leasing, without changing any addressing.

Topology

  • DHCP server 10.0.0.2/24, default route via the router
  • Router: Ethernet1 10.0.0.1/24 (server segment), Ethernet2 10.0.50.1/24 (client A), Ethernet3 10.0.60.1/24 (client B)
  • One client on each of 10.0.50.0/24 and 10.0.60.0/24

Your job

Make the router relay DHCP for both client subnets toward the central server, so a client on either segment can lease an address.

What "done" looks like

Both 10.0.50.0/24 and 10.0.60.0/24 are relayed to 10.0.0.2, and the server has a working return path to each.

Teaches: a DHCP relay (ip helper-address) is per-interface: every client subnet that needs the central server needs its own relay, and leases only work if the return path exists too.

What gets checked

Your solution is verified against each of these:

  • The router relays DHCP for 10.0.50.0/24 toward the central server (10.0.0.2)
  • The router relays DHCP for 10.0.60.0/24 toward the central server (10.0.0.2)
  • Both client subnets are relayed and the server has a return path to each

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