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2. Objectives Understand the process of name resolution using HOSTS, DNS, and WINS Identify basic configuration parameters for a DNS server Use nslookup and nbtstat to verify and troubleshoot name resolution Install and configure DHCP and NTP servers 2.4 Network Services 139

3. Host name o Letters, numbers, and hyphen o Cannot be all numbers o Cannot start or end with hyphen o Not case sensitive Fully Qualified Domain Name (FQDN) o Host name + domain suffix o Host name must be unique within domain o Labels separated by periods o Max length of 253 characters overall and 63 characters per label (excluding periods) Host Names and FQDNs 2.4 Network Services 139

4. HOSTS was a text file containing list of IP > host name or FQDN mappings Distributed manually between network administrators Long replaced by Domain Name System (DNS) but each host is still installed with HOSTS file o Windows − %SystemRoot%\System32\drivers\etc\hosts o Linux − /etc/hosts Administrators can configure static mappings in HOSTS and these take precedence over DNS Name Resolution using HOSTS 2.4 Network Services 141

5. Domain Name System (DNS) Hierarchical database of IP and name records Root domain contains 13 servers (A…M) Top Level Domains (TLD) managed by ICANN and regional registries Domains can be registered within an appropriate TLD 2.4 Network Services 141

6. Name Resolution using DNS 2.4 Network Services 142

7. Service port o UDP Port 53 o TCP Port 53 Zones o Primary o Secondary o Cache-only Iterative versus recursive queries Configuring DNS Servers 2.4 Network Services 144

8. Resource Records 2.4 Network Services 145

9. Allows clients to notify DNS server of IP address changes Might be implemented through DHCP on enterprise network – update packets must be authenticated Update to DNS server records may be requested by host Internet dynamic DNS services can be used with SOHO routers (where ISP does not allocate fixed IP address) Dynamic DNS 2.4 Network Services 146

10. Query a name server for resource records nslookup –Option Host Server Interactive mode nslookup 2.4 Network Services 147

11. NetBIOS over TCP/IP o Supports legacy clients and applications Uses UDP port 137 and TCP port 139 or TCP port 445 nbtstat used to query name information NetBIOS and nbtstat 2.4 Network Services 148

12. DHCP Server A range of IP addresses to allocate (its scope) A subnet mask to allocate Other optional information to allocate, such as default gateway and DNS A lease period 2.4 Network Services 150

13. Options are customizable but typical parameters include o The default gateway (IP address of the router) o The IP address(es) of DNS servers o The DNS suffix (domain name) to be used by the client o Other useful server options, such as time synchronization (NTP), file transfer (TFTP), or VoIP proxy Static assignments / reservations o Always allocate a device (identified by MAC address) the same IP o Automatic allocation – lease an IP address (any IP address) to the same client permanently Options and Reservations 2.4 Network Services 152

14. DHCP broadcast traffic not normally forwarded by routers Would mean DHCP server for each subnet / VLAN DHCP relay agent / RFC 1542 compliant router o Forwards BOOTP / DHCP traffic broadcasts to specified interface for a DHCP server o Forwards responses from server back to appropriate client subnet ip-helper o Cisco command supporting operation of DHCP relay o Can forward various types of broadcast traffic (not just DHCP) DHCP Relay and IP Helper 2.4 Network Services 153

15. Network Time Protocol (NTP) 2.4 Network Services 153

16. Review Understand the process of name resolution using HOSTS, DNS, and WINS Identify basic configuration parameters for a DNS server Use nslookup and nbtstat to verify and troubleshoot name resolution Install and configure DHCP and NTP servers 2.4 Network Services 154