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The Domain Name System (DNS), & Other Important ‘Utility’ Protocols 635.413.31 – Summer 2007 Why is name resolution necessary? Allows the use of easily remembered names to access Internet resources instead of IP addresses Really set the stage for mass adoption of the Internet
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Top Level Domains are currently organized into 3 different ‘groups’
1. The Organizational Top Level Domains or ‘generic’ TLDs
2. The Geographic Top Level Domains
3. The ARPA Top Level Domain
> nslookup www.yahoo.com
Addresses: 126.96.36.199, 188.8.131.52, 184.108.40.206, 220.127.116.11
18.104.22.168, 22.214.171.124, 126.96.36.199, 188.8.131.52
> dig umd.edu mx
; <<>> DiG 8.3 <<>> umd.edu mx
;; res options: init recurs defnam dnsrch
;; got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 2
;; flags: qr aa rd ra; QUERY: 1, ANSWER: 2, AUTHORITY: 3, ADDITIONAL: 5
;; QUERY SECTION:
;; umd.edu, type = MX, class = IN
;; ANSWER SECTION:
umd.edu. 16h40m IN MX 10 mailfw1.umd.edu.
umd.edu. 16h40m IN MX 10 mailfw0.umd.edu.
;; AUTHORITY SECTION:
umd.edu. 16h40m IN NS ns2.umd.edu.
umd.edu. 16h40m IN NS noc.umd.edu.
umd.edu. 16h40m IN NS ns1.umd.edu.
;; ADDITIONAL SECTION:
mailfw0.umd.edu. 5M IN A 184.108.40.206
mailfw1.umd.edu. 10M IN A 220.127.116.11
noc.umd.edu. 5M IN A 18.104.22.168
ns1.umd.edu. 16h40m IN A 22.214.171.124
ns2.umd.edu. 16h40m IN A 126.96.36.199
A typical example for a diskless workstation
BOOTP Server Design
DHCP has two major advantages over BOOTP:
1. Client boots
2. Client broadcasts DHCP Discover message
3. One or more servers responds with a DHCP Offer message containing IP address and network configuration parameters based on the DHCP administrator’s policies
4. The client chooses one of the DHCP Offer messages and broadcasts a DHCP Request with the chosen server specified in the ‘server identifier’ field – all other DHCP servers that responded with offers know by examining the request that they were not chosen
5. The chosen DHCP server receives the Request message and commits the client’s assigned address in its database. The server responds (typically unicast) to the client with a DHCP ACK confirming successful reservation of the IP address
6. After receiving the DHCP ACK the client should be fully configured and able to communicate on the TCP/IP network