Networks 07

1
Networks 07

• Host Configuration Protocols

2
Warning!!!

• Glen
• Dont play with any of this on production
  networks unless you own those networks.
• Dont use the default config files
• RTFM and STFW first

3
DHCP

• Dynamic Host Configuration Protocol can be used
  to obtain IP address, subnet mask, default
  gateway, DNS servers, and other settings.
• Replaces the earlier BOOTP protocol, which only
  allowed a subset of these
• Defined by RFC 2131

4
DHCP

• Client binds 0.0.0.0, port 68
• Broadcast discovery (to port 67)
• Unicast responses
• DHCP relays can be used to convert broadcast
  request into a unicast one
• Why are there three offers ACKs below?

5
DHCP

• Id db.DHCP,v 1.87 2006/09/17 050417 guy Exp
  
• option domain-name "ru.ac.za"
• option domain-name-servers 146.231.129.98,
  146.231.129.97, 146.231.129.102
• option ntp-servers 146.231.129.81,
  146.231.129.82, 146.231.129.86
• option ip-forwarding off
• default-lease-time 600
• max-lease-time 172800
• option time-offset 7200
• option netbios-node-type 8
• option netbios-name-servers 146.231.128.57
• option netbios-dd-server 146.231.128.57
• option wpad code 252 text
• option wpad
  "http//www.ru.ac.za/proxy.pac\n"
• not authoritative
• ddns-update-style none
• shared-network RHODES-example
• subnet 146.231.2.0 netmask
  255.255.255.248
• option routers
  146.231.2.1

6
Router Solicitation

• Allows IPv6-enabled hosts to discover their
  (default) router and prefix length
• Cant set other options
• Built in part of IPv6
• ICMP-based
• AKA stateless address autoconfiguration

7
DHCPv6

• Provides the extra information that router
  solicitation cant, such as
• UDP ports 546 (client) and 547 (server)
• Not widely implemented yet

8
Web Proxy Auto Discovery

• Higher level discovery protocol used by browsers
  to discover their proxy settings
• Not an Internet standard draft-ietf-wrec-wpad
• Works in one of two ways
• DHCP option 252
• HTTP request to
• http//wpad.ict.ru.ac.za/wpad.dat
• http//wpad.ru.ac.za/wpad.dat
• http//wpad.ac.za/wpad.dat
• Expects a Javascript proxy auto-config file to be
  returned