Andrew Smith 1 NAT and DHCP ( Network Address Translation and Dynamic Host Configuration Protocol )

Andrew Smith 2 NAT and DHCP This session will cover The sharing of one (or a few IP address) by translation Reduction of demand for ‘internet’ IP addresses The automatic issue of IP addresses to a host on a large scale system, without the need to configure the host

Andrew Smith 3 NAT and DHCP WE will be working on a derivation of the standard WAN Mesh used in all Day Schools

Andrew Smith 4 NAT and DHCP NAT (Network Address Translation) Used to aggregate (collect) a range of addresses, usually private into one (or few) externally recognisable addresses

Andrew Smith 5 NAT and DHCP NAT (Network Address Translation) Cisco defines the following NAT terms: –Inside local address – The IP address assigned to a host on the inside network. The address is usually not an IP address assigned by the Internet Network Information Center (InterNIC) or service provider. This address is likely to be an RFC 1918 private address. –Inside global address – A legitimate IP address assigned by the InterNIC or service provider that represents one or more inside local IP addresses to the outside world. –Outside local address – The IP address of an outside host as it is known to the hosts on the inside network. –Outside global address – The IP address assigned to a host on the outside network. The owner of the host assigns this address.

Andrew Smith 6 NAT and DHCP NAT (Network Address Translation) Inside Local Inside global address 10.x.x.x translated as Outside global address Outside global address, when is seen as to the local hosts

Andrew Smith 7 NAT and DHCP NAT (Network Address Translation) Normally NAT will translate a range of address to a network For example you could have 10.x.x.x translated to – PAT (Port Address Translation) uses one address and sends each connection on a new (unique TCP port) with the potential of though most systems (routers) can only cope with 2000

Andrew Smith 8 NAT and DHCP NAT (Network Address Translation) PAT (Port Address Translation) uses one address and sends each connection on a new (unique TCP port) with the potential of though most systems (routers) can only cope with 2000 This means 10.x.x.x, x.x or x.x can be translated through one address, most of your ADSL/Broadband routers do this

Andrew Smith 9 NAT and DHCP NAT (Network Address Translation) Static translation, the creation of a 1:1 relationship between and external and internal address, completed when you have an externally facing server (like mail or web) on a NAT translated network Dynamic translation, when a host is allocated an address or ‘port’ via NAT/PAT

Andrew Smith 10 NAT and DHCP NAT (Network Address Translation) Static translation, the creation of a 1:1 relationship between and external and internal address, completed when you have an externally facing server (like mail or web) on a NAT translated network Dynamic translation, when a host is allocated an address or ‘port’ via NAT/PAT

Andrew Smith 11 NAT and DHCP DHCP (Dynamic Host Configuration Protocol) Allowing a ‘large’ or ‘small’ scale system to issue addresses to all hosts (from workstations to servers and printers) rather than the admin having to set the IP address on each device. The address is leased, for a defined period of time. Your ISP may do this, your ADSL/Broadband router may do this

Andrew Smith 12 NAT and DHCP DHCP (Dynamic Host Configuration Protocol) Done using UDP, on ports 67 (DHCP server) and 68 (DHCP host) The host must receive –An issued IP address –The Default Gateway address (which may also be the router, but please be aware a DHCP server can run autonomously) –Subnet mask –DNS server address, which may be internal or externally available WINS, Domain name and other parameters can also be issued

Andrew Smith 13 NAT and DHCP DHCP (Dynamic Host Configuration Protocol) Addresses may be issued by –Automatic allocation – DHCP assigns a permanent IP address to a client. –Manual allocation – The IP address for the client is assigned by the administrator. DHCP conveys the address to the client. –Dynamic allocation – DHCP assigns, or leases, an IP address to the client for a limited period of time.

Andrew Smith 14 NAT and DHCP NAT and DHCP configuration Please ensure your router (s) are configured as per the normal infra- structure

Andrew Smith 15 NAT and DHCP NAT configuration access-list 1 permit ip nat inside source list 1 interface FastEthernet0/0 overload interface fastethernet 0/0 ip nat inside interface serial0/0 ip nat outside

Andrew Smith 16 NAT and DHCP DHCP configuration service dhcp ip dhcp pool sanfranciscopool network default-router dns-server domain-name widgetsrus.co.uk netbios-name-server Exit ip dhcp excluded-address

Andrew Smith 17 NAT and DHCP Testing the configuration To check DHCP Run ‘ipconfig’ to check the DHCP address has been obtained Run ‘ipconfig /release’ to remove an automatic addressing. Run ‘ipconfig /renew’ to receive a new DHCP licensed address To check NAT You must ping the nearside interface on the afar router from the host on the LAN For example, from the computer on the Madrid LAN you must ping –t, note the ‘-t’ means continuous (no timeout) On each router, issue the ‘clear ip nat translation *’ command ‘show ip nat translations’ command

Andrew Smith 18 NAT and DHCP

Andrew Smith 19 NAT and DHCP