Sample DNS configurations

Example 1: Master 'master' DNS and is authoritative for this zone for example.com provides 'caching' services for all other domains provides recursive query services to local resolvers only (a closed DNS)

Example 2: Slave ‘Slave’ DNS for this zone for example.com Gets its information from the zone master and is authoritative when it has a valid zone configuration. provides 'caching' services for all other domains provides recursive query services to local resolvers only (a closed DNS)

Example 3: Caching only server The name server is not a 'master' or 'slave' for any domain All BIND servers will cache previous queries until TTL expires Provides 'caching' services for all other domains Provides recursive query services to local resolvers only (a closed DNS) [Could act as caching only for some domains, master for other domains (zones)]

Example 4: Forwarding server Also known as Proxy, Remote and Client Server The name server is not a 'master' or 'slave' for any domain All requests are forwarded to the specified forwarders Only means it will stop if the forwarders have no answer default is first – start with forwarders and then look elsewhere Reduces network traffic – particularly over a slow link.

Example 5: Stealth server Also known as DMZ or Split Server Need for a public DNS to enable access to web, mail ftp etc.. Does not want the world to see any of its internal hosts either by interrogation (query or zone transfer) or should the DNS service be compromised.

Example 5: Stealth server How?

The zone file for the 'Stealth' server will contain both public and private hosts Whereas the 'Public' server's master zone file will contain only public hosts. Options such as 'master', 'allow-notify','allow- transfer' must not refer to the Stealth Server Example 5: Stealth server

DHCP Dynamic Host Configuration Protocol

DHCP Dynamic Host Configuration Protocol Provides services to both DHCP and BOOTP clients DHCP/BOOTP Clients request and are granted IP addresses (and other information about themselves and the network) Best to have only one machine on an Ethernet segment (VLAN) is designated a DHCP server

DHCP Service Profile System-V Managed Service Daemon: dhcpd Script: dhcpd Ports: 67 (bootps) 68 (bootpc) Configuration: /etc/dhcpd.conf /var/lib/dhcp/dhcp.leases Client: dhclient

DHCP Configuration /etc/dhcpd.conf Must have a broadcast address specified for the relevant interface (ifconfig) Leases are recorded in /var/lib/dhcp/dhcpd.leases as they are assigned

DHCP

DHCP Information Typically a DHCP server will supply information about the network’s subnet address and mask The default gateway Domain Name and DNS Servers Locations of kick-start configuration files (for diskless clients) DHCP is a superset of BOOTP BOOTP does not have the notion of a ‘lease’ period

DHCP – How it works DHCP Client sends a DHCP Discover message Subnet broadcast address as destination as source address DHCP server responds with a DHCP Offer message Includes a suggested IP address to use

DHCP – How it works DHCP Client receives DHCP Offer and sends DHCP Request Message DHCP Server receives DHCP Request and sends a DHCP Ack message DHCP Client receives DHCP Ack message Configures TCP/IP stack to use the address Other messages: DHCP Inform DHCP Release

Configuration in /etc/dhcp.conf #global settings option domain-name “example.com” option domain-name-servers default –lease-time # 6 hours to expiry max-lease-time # max lease time

Dynamic/Static IP Addresses IP addresses are either assigned dynamically from a pool of available addresses or Statically, based on the MAC address of the requesting machine. This is usually called a reservation The assigned IP address is made available for a configurable amount of time, the ‘lease’ period, and may be renewed by the client

DHCP Configuration by scope # DHCP scope settings subnet netmask { range ; option domain-name “example.com”; option routers ; host station1{ hardware ethernet 00:ab:08:33:cd:92; fixed-address ; }