Before going to today's topic...

• There were many who don't know HUB and Router.
  • :-<
• HUB
  • Extends a network
• Router
  • Connects two or more networks

Therefore,

• HUB is related to Ethernet
• Router is related to Internet

Let's find HUB and Router (1)

Let's find HUB and Router (2)

Let's find HUB and Router (3)

Let's find HUB and Router (4)

Let's find HUB and Router (5)

Let's find HUB and Router (6)

Other late questions

• what are the commands for getting IP/MAC address etc
• ifconfig -a ... for IP/MAC
• netstat -r ... for (default) routers
• arp -a ... for IP/MACs on your network

Miscellaneous

• Loopback interface
• Your own host ... localhost
• IP address = 127.0.0.1
• Worlds worst hacker (Joke)

Miscellaneous

• Private address ... no use for global routing
• 10.0.0.0 -- 10.255.255.255
• 172.16.0.0 -- 172.31.255.255
• 192.168.0.0 - 192.168.255.255

DNS/WHOIS

• IP address to/from host name mapping
• who owns this IP/domain ?

DNS

• Domain Name System
• Specify DNS Server (DHCP or manually)
• Ask your DNS by (ip/hostname)
• Your DNS returns (hostname/ip)

host/dig commands

• Read the manual and try.
• dig returns more elaborated answers

How your DNS works

• Ask . DNS server for www.kochi-u.ac.jp
• . returns jp DNS server
• Ask jp DNS server for www.kochi-u.ac.jp
• jp returns kochi-u.ac.jp DNS server
• Ask kochi-u.ac.jp DNS server for www.kochi-u.ac.jp
• kochi-u.ac.jp returns ip address of www.kochi-u.ac.jp

Root Servers

• serves for . domain
• a.root-servers.net ... m.root-servers.net
• How to find root servers

Reverse Lookup

• www.kochi-u.ac.jp >>> . -> jp -> ac -> kochi-u -> www -> 133.97.2.55
• 133.97.2.55 -> ?
• 55.2.97.133.in-addr.arpa >>> . -> in-addr.arpa -> 133 -> 97 -> 2 -> 55

Type of Records

• A ... IPv4 address
• PTR ... Pointer (Reverse Look-up)
• AAAA ... IPv6 address
• Others follow ...

MX

• mail exchange
• Gateway to other mail system (UUCP/X.500/mobile)

CNAME

• Canonical Name
• alias => canonical name

SOA

• Start of Authority
• Whats in there?

Distributed Database

• DNS is a highly coordinated distributed database
• many rules
• DNS related RFCs

Tools

• host, dig, nslookup
• Python
  • socket.gethostbyname()
  • socket.gethostbyaddr()

Whois

• Another DB for Internet Information
• who owns this IP/domain ?
• RFC954
• subquery is implemented in whois command
• depends on implementation
• whois -h whois.nic.ad.jp TK197JP

Quiz of the day

• What command do you use if you want to ...
• know the IP address of www.whitehouse.gov ?
• know who is attacking my server ? I know his IP address.

Homework

• Collect information of your mail domain using DNS and Whois.
• Your mail domain is outside of kochi-u.ac.jp.
• If you don't have other email address, then try kochi-u.ac.jp.