DHCP, DNS, NAT and NTP
Topic 12 of 26. 31 questions: 15 pick one, 4 pick all, 5 type it, 3 put in order, 4 interview
What this topic covers
- DHCP DORA and the messages
- DHCP relay and ip helper-address
- DHCP options 3 6 43 66 150
- lease renewal T1 T2
- DNS resolution recursive vs iterative
- DNS record types A AAAA CNAME MX NS PTR SOA TXT SRV
- TTL and caching
- DNS over UDP and TCP 53
- NAT static dynamic and PAT
- inside outside local global
- NAT order of operations
- port forwarding
- NAT and protocols that break
- NTP strata and why time matters
- file transfer TFTP FTP SCP SFTP
Study it in depth on Octet.
- 1Put the DHCP messages a new client exchanges with the server in the order they are sent, first to last.
- 2Two DHCP servers on the same VLAN both answer a client's DISCOVER. How does the server whose offer was not taken find out?
- 3Which of these DHCP messages are sent by the client? Choose all that apply.
- 4SW1 relays a DISCOVER from a PC in VLAN 20 to the DHCP server 10.0.12.10. SW1 reaches the server through a routed uplink whose address is 10.0.99.2. Which address does SW1 write into the giaddr field?
- 5Users on LAN B (10.20.0.0/24, behind R2) get 169.254.x.x addresses. R1 at 10.0.12.1 is the DHCP server and has a pool for LAN B. Based on R2's configuration, what is wrong?
- 6PCs on 10.20.0.0/24 behind relay R2 never get an address. R1 is the DHCP server. Based on this output from R1, what is the cause?
- 7Which DHCP option number carries the default gateway (the router list) for the client?
- 8IP phones download their configuration from a TFTP server they learn through DHCP. Which DHCP options can carry that TFTP server? Choose all that apply.
- 9Cisco lightweight access points in this pool use DHCP option 43 to find their wireless LAN controller. Which controller IP address does an AP learn?
- 10A client has reached T1, half of its DHCP lease. How does it try to renew?
- 11A client gets a 24-hour DHCP lease and the server uses the default timers. After how many hours does the client start broadcasting rebind requests to any server (T2)?
- 12A DHCP client's server has died and never answers again. Put the client states in the order the client passes through them, from holding a fresh lease to looking for a new server.
- 13A Windows PC shows the IPv4 address 169.254.37.12. What does that tell you?
- 14You create a new VLAN for 200 users, and the DHCP server sits in the data center. Explain how clients in the new VLAN get addresses and what has to be in place.
- 15Which file transfer protocol runs as a subsystem of SSH and supports listing directories, resuming transfers and renaming files?
- 16Which of these protect both the login credentials and the file contents in transit? Choose all that apply.
- 17Copying a 30 MB file with TFTP across a WAN with 50 ms of round-trip time takes close to an hour, although the link is fast. Why?
- 18Compare TFTP, FTP, SCP and SFTP. Which would you use to load a new software image onto a router, and why?
- 19A laptop asks the company resolver for www.example.com, which the resolver has not cached. Which kinds of query are used along the way?
- 20Put the steps of resolving www.example.com in order, first to last, for a resolver that starts with an empty cache.
- 21A sending mail server has a message for user@example.com. Which host does it try to deliver to first? Give the host name.
- 22Which name does a resolver look up to find the PTR record for the IPv4 address 192.0.2.25?
- 23A developer wants example.com itself, the zone apex, to be a CNAME pointing at a cloud load balancer's host name. Why does standard DNS not allow it?
- 24How do Active Directory clients find a domain controller for their domain?
- 25A recursive resolver receives this answer from the authoritative server. For how many seconds may it cache the fact that api.example.com does not exist?
- 26An hour ago the team changed www.example.com from 198.51.100.20 to 203.0.113.80. Office users, who use the resolver 10.0.0.53, still reach the old server. What explains this output?
- 27In which of these cases does DNS use TCP port 53? Choose all that apply.
- 28Most names resolve through the internal resolver 10.0.0.53, but lookups of large TXT records fail. Based on this output, what is the most likely cause?
- 29An admin edits the example.com zone file on the primary server, reloads it and forgets to raise the SOA serial. What happens?
- 30Walk me through what happens when a client resolves www.example.com.
- 31You must move www.example.com, which has a 24-hour TTL, to a new IP address with as little disruption as possible. How do you handle DNS?