DHCP leases, scopes and APIPA 169.254 addresses for A+

Try 3 questions on this

Pick an answer to see why each option is right or wrong.

1. An office's DHCP server has failed, and a workstation has assigned itself a 169.254.x.x address. It reaches another self-addressed workstation on its switch, but not a file server on another subnet, even after the technician enters the router as its gateway. Which of the following should the technician configure until the server is repaired?

   Right. In the game that’s Renown for your Networking building.

   Not that one: B is right. In the game your Networking building would lose a little Renown, and this question would come back later.

   Your answerA.Dynamic IP addressA dynamic address comes from the DHCP server, which is the device that has failed. Until it is back, the workstation keeps its self-assigned address.The answerB.Static IP addressRFC 3927 says a router must not forward a packet with a 169.254 (link-local) source or destination address, whatever its routes.Your answerC.Subnet maskChanging the mask does not change the 169.254 address, and RFC 3927 says routers must not forward packets from that range.Your answerD.Default gatewayRFC 3927 says routers must not forward link-local packets regardless of their routes, so pointing the workstation at the router does not get its traffic off the local link.

   Show the full explanation and doc quotes

   The workstation therefore needs a routable address, and with DHCP down the RFC's other way to get one is manual configuration: a static IP address on the office subnet.

   Written from www.rfc-editor.org/rfc/rfc3927.html

2. A laptop that stays powered on and connected all day receives an IPv4 address from the office's DHCP server, which uses default renewal timing. A technician captures the laptop's traffic to see when it first tries to extend that lease. Which of the following describes when this happens?

   Right. In the game that’s Renown for your Networking building.

   Not that one: B is right. In the game your Networking building would lose a little Renown, and this question would come back later.

   Your answerA.When the lease time runs outRFC 2131 says that if the lease expires before the client receives an acknowledgment, the client must immediately stop network processing and start over. Clients try to extend the lease well before that point.The answerB.After half of the lease timeRFC 2131 says the client keeps two timers for extending its lease, and that T1 defaults to 0.5 times the lease duration while T2 defaults to 0.875 times it.Your answerC.After seven-eighths of the lease timeThis is T2, which defaults to 0.875 of the lease. The client reaches it only if its first request, sent at half the lease, got no answer; it then broadcasts to any server.Your answerD.When the server prompts it to renewThe client tracks its own lease times and sends the request itself; RFC 2131 has the client, not the server, start the renewal.

   Show the full explanation and doc quotes

   At T1 the client first sends a request to the server that issued the address, so with default timing the first attempt comes after half of the lease.

   Written from www.rfc-editor.org/rfc/rfc2131.html

3. An office's DHCP server leases addresses to clients on the first-floor subnet. A router now forwards DHCP broadcasts from a new second-floor subnet to that server, but second-floor laptops still receive no addresses. Which of the following should the administrator do?

   Right. In the game that’s Renown for your Networking building.

   Not that one: D is right. In the game your Networking building would lose a little Renown, and this question would come back later.

   Your answerA.Install a new DHCP server on the second floor.A second DHCP server on the second floor would hand out addresses, but the router already forwards that floor's requests. The guide pairs forwarding with one scope per subnet and calls it the more cost-effective design in most cases.Your answerB.Lengthen the existing scope's lease duration.The lease duration only sets how long a client keeps an address. The server has no scope for the second-floor subnet, so it has nothing to lease there.Your answerC.Add an exclusion range to the existing scope.An exclusion range stops the server offering some addresses inside a scope. It cannot give the server addresses for a subnet it has no scope for.The answerD.Create a new scope on the DHCP server.Microsoft's DHCP deployment guide gives two ways to serve several subnets: a DHCP server on each subnet, or routers that forward DHCP broadcasts plus one scope per subnet on the server.

   Show the full explanation and doc quotes

   The router already forwards the second floor's requests, so the missing piece is a scope for that subnet; the guide adds that forwarding is in most cases more cost effective than a server on each segment.

   Written from learn.microsoft.com/en-us/windows-server/networking/technologies/dhcp/dhcp-deploy-wps