tcpip - Day 2

Goals

• leverage your knowledge of DNS to explore new tools:
• nslookup
• dig
• netstat
• learn about subnetting

POST

1. How many IPs are there in a Class C netblock? How many usable IPs?
2. In a Class B (rough estimate)?
3. In a Class A (rough estimate)?
4. what is the usual designation for a network? (assume 111.222.111.xxx)
5. what is the usual broadcast address for a network? (assume 111.222.111.xxx)
6. what is the broadcast for anyhow?
7. what forces act to decrease the effective number of IPs?
8. what forces act to increase the effective number of IPs
9. why would the network want to segment (shorten/multiply) packets?
10. which name resolution came first: "hosts" file or DNS?
11. how are both used today?
12. what resources does a registrar control?
13. why do you need a DNS server in your unix/windows tcpip setup?
14. why might you need a secondary DNS server?

Learning about your current network

dns utilities

• see an actual dns record, primary and secondary
• nslookup: man nslookup p. 341-46
  • shell mode: nslookup hostname or nslookup hostname name server
  • interactive: help, set, lserver, debug, set query=, set domain=, set type=mx (for mail), set type=WKS (well known services)
  Sample output:

  Server:  ns1.airmail.net
  Address:  206.66.12.36
  
  Non-authoritative answer:
  ripper.jbagroup.net     internet address = 66.12.130.221
  
  Authoritative answers can be found from:
  jbagroup.net    nameserver = ripper.jbagroup.net
  ripper.jbagroup.net     internet address = 66.12.130.221
  

• dig hostname. man dig dig @nameserver host type. pp. 347-48. Sample output:

  ; <<>> DiG 8.3 <<>> www.jbagroup.net
  ;; res options: init recurs defnam dnsrch
  ;; got answer:
  ;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 4
  ;; flags: qr aa rd ra; QUERY: 1, ANSWER: 2, AUTHORITY: 1, ADDITIONAL: 1
  ;; QUERY SECTION:
  ;;      www.jbagroup.net, type = A, class = IN
  
  ;; ANSWER SECTION:
  www.jbagroup.net.       1D IN CNAME     ripper.jbagroup.net.
  ripper.jbagroup.net.    1D IN A         66.12.130.221
  
  ;; AUTHORITY SECTION:
  jbagroup.net.           1D IN NS        ripper.jbagroup.net.
  
  ;; ADDITIONAL SECTION:
  ripper.jbagroup.net.    1D IN A         66.12.130.221
  
  ;; Total query time: 14 msec
  ;; FROM: malkuth to SERVER: default -- 127.0.0.1
  

• whois, web whois. whois domain/ip

network utilities

• ping, -s, floods, icmp
• traceroute, traceroute, external traceroute. Sends UDP packets - unreliable. Max hops.
• arp -a
• netstat -a, --programs, --route, --tcp, --udp
• ifconfig -a, promiscuous mode. man ifconfig.
• route (may not be available to non-root)

subnetting