200-301 - IP Services - Section 4.1

Configure and verify inside source NAT using static entries and pools, NTP in client and server mode, and DHCP client and relay, and explain the role of DHCP and DNS in the network.

Translate private inside addresses to public addresses with static NAT for one-to-one mappings and pool-based or PAT overload for many-to-one, and verify the translation table. Synchronise device clocks with NTP in client/server mode, and explain how DHCP leases addressing to clients - including DHCP relay (ip helper-address) when the server is on another subnet - while DNS resolves names to addresses.

Inside source NATPAT overloadNTP client and serverDHCP and DHCP relayDNS

Practice question for this objective

Free sampleIP Servicesmedium

R1 is the internet edge router. Hosts on the inside use 10.1.1.0/24, and the ISP has assigned the public address 203.0.113.10 to reach an internal web server at 10.1.1.10. The administrator wants outside clients to always reach the server at the fixed public address. The following configuration is already in place: interface GigabitEthernet0/0 ip address 10.1.1.1 255.255.255.0 ip nat inside ! interface GigabitEthernet0/1 ip address 203.0.113.1 255.255.255.0 ip nat outside Which single additional command completes a working inside source static NAT for the server?

interface GigabitEthernet0/0
 description LAN to 10.1.1.0/24
 ip address 10.1.1.1 255.255.255.0
 ip nat inside
!
interface GigabitEthernet0/1
 description WAN to ISP
 ip address 203.0.113.2 255.255.255.252
 ip nat outside
  • Aip nat inside source static 10.1.1.10 203.0.113.10 Correct
  • Bip nat inside source static 203.0.113.10 10.1.1.10
  • Cip nat outside source static 10.1.1.10 203.0.113.10
  • Dip nat inside source static tcp 10.1.1.10 80 203.0.113.10 80 extendable
Configure inside source static NAT by placing the inside local address before the inside global address with interfaces marked nat inside and outside. Inside source static NAT creates a permanent one-to-one mapping written as inside local then inside global. With Gi0/0 marked ip nat inside and Gi0/1 marked ip nat outside, the command ip nat inside source static 10.1.1.10 203.0.113.10 translates the private server to the public address in both directions.

Why A is correct: Inside source static takes the inside local address first then the inside global address, so this maps private host 10.1.1.10 to public 203.0.113.10 in both directions, exactly what a one-to-one server mapping needs with the interfaces already marked inside and outside.

Why B is wrong: This reverses the operands. In inside source static the inside local (private) address comes first and the inside global (public) address second, so this would advertise the public address as if it were the private host and fails to translate the server.

Why C is wrong: Outside source static translates addresses that live on the outside network back into the inside, which is the wrong direction for publishing an internal server, so the inside host would never be reachable at the public address.

Why D is wrong: This is a port-forwarding (PAT static) entry that only maps TCP port 80, so it is tempting but narrower than the requirement to reach the whole server at the fixed public address rather than a single service port.

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