IP Address Resolution
ARP Address Resolution Protocol
Part of the TCP/IP protocol suite
Used to find the MAC address for a given IP address
uses broadcasts
When the MAC address is discovered the packet/frames can then be sent to the correct destination without broadcasting
the IP address to MAC address mapping is cached for a period of time
At the command prompt:
arp a shows the current contents of the arp cache
arp d <ip
address>
eg arp d 10.0.0.1
deletes the specified address from the cache
arp s <ip address> <MAC address>
eg arp s 10.0.0.1 12-b3-5a-68-f1-22
adds the address and corresponding MAC address to the cache permanently (static
entries)
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DNS Domain Name System
Used by TCP/IP
The Internet uses
DNS
Example: www.geocities.com/peteswebuk
(this is a Fully Qualified Domain Name (FQDN)
as it gives us the exact address of the computer)
The DNS namespace
Zones
A zone must cover a contiguous namespace
A DNS server stores a zones database containing the name to IP address mappings
A DNS server can serve multiple zones
There can be multiple DNS servers for one zone
Forward look-up query resolution process
Client sends query for www.geocities.com/peteswebuk to local DNS server
As local server has no authority for www.geocities.com/peteswebuk it forwards the query to the root DNS server which returns referral to com DNS server.
Com DNS server is contacted and returns referral to www.geocities.com DNS server.
geocities.com DNS server is contacted and because it has authority for that namespace portion it sends back IP address of www.geocities.com/peteswebuk to local DNS server
Local DNS server forwards IP address to client.
Resolution process finished, client uses IP address to contact www.geocities.com/peteswebuk directly.
Name server caching
As a name server process a query it discovers the IP address of severs that have authority over portions of the namespace and it caches this information to make future queries quicker.
This cached information expires after a certain time.