Transcript Chapter 17 Windows Internet Name Service WINS

Chapter 17
Windows Internet Name Service
WINS
WINS
• A NetBios name server that resolves
NetBIOS name to IP addresses
• Is much like DNS, with clients registering
names and performing name lookup, and
servers handling the registration and
resolution
What is a NetBIOS Name?
• Microsoft networks always use NetBIOS names to identify
network resources
• Machines recognize each other through their unique
NetBIOS machine name
• Shared resources, files, and printers are accessed using
NetBIOS names
• A Universal Naming Convention (UNC) is used
• Example: \\servername\share_name
• Servername is NetBIOS name of the machine where the
resource is located
• Share_name is the NetBIOS name uniquely identifying the
resource
What Processes Use NetBIOS?
• Windows file sharing service
• Browser service
Benefits of WINS
• WINS is a dynamic database that minimizes
maintenance required by administrator
• WINS is a centralized NetBIOS name
management system
• Eliminates the need for static LMHOSTS files,
unless they are used in addition to WINS server
• Decreases broadcast traffic
How are NetBIOS Names Resolved?
• LMHOSTS
– Locally stored ASCII text file
• WINS
– Server that does NetBIOS to IP name resolution
NetBIOS Names
• NetBIOS name space is flat, unlike DNS that uses
a hierarchical name space
• The name is unique on an internetwork
NetBIOS Node Types
• B-Node
– Name registration and name resolution are performed
using broadcast only
– Best option for small, single subnet networks
• P-Node
– Name registration and name resolution are done using
WINS
– Eliminates local subnet broadcasts
– May cause network resources on a local subnet to not
be resolved
NetBIOS Node Types - Cont.
• M-Node
– A combination of B-Node and P-Node
– Name registration and resolution are done by broadcast
– If broadcast is not successful, the name server (WINS)
is used
– This is useful when WINS server is on a remote
network
– Attempt is made to resolve name locally first before
using WAN resources for the resolution
NetBIOS Node Types – Cont
• H-Node
– A combination of P-Node and B-Node
– Name registration and resolution are attempted first
using WINS server
– If this is not successful, then broadcast is used
– WINS uses H-Node
NetBIOS Name Registration
• When a resource becomes available for use, the network
resource must register its NetBIOS name
• The registration process ensures that the name being
registered isn’t already in use
• Process may include broadcasts, but with WINS server, the
name registration query message is sent directly to the
WINS server and is registered in the database
• The registration query includes the soure IP address and
the NetBIOS name, along with the destination computer’s
IP address
• In order to have your computer register its NetBIOS name
with the WINS server, all you have to do is configure your
client to use WINS (see demonstration of this)
Name Registration – Cont.
• The WINS server checks the database for the NetBIOS
name
• If the name is not found, the WINS server sends a positive
name registration response which designates a time at
which the client needs to renew its registration
• If the entry already exists in the database, the server
challenges the holder of the current registration to respond.
If the current holder responds successfully, a negative
registration response is sent to the computer trying to
register the name
Renewing Names
• NetBIOS names registered with a WINS server have a
limited life and must be refreshed before their life expires
• This time is referred to as Time To Live (TTL)
• The default TTL is 6 days
• A WINS client tries to renew any NetBIOS names it holds
at half the TTL
• Each time the computer is restarted, a new name
registration message is sent to the WINS server to renew
the name
Releasing of NetBIOS names
• Can occur two ways:
– Computer can release any held NetBIOS name by
sending the WINS server a Name Release message
containing the NetBIOS name to release
– If an end-node fails to renew the name, that name will
become free to be used by another end-node
Resolving NetBios Nmaes
• A client that needs to resolve a NetBIOS name
issues a NetBIOS Name Query Request, either by
using a broadcast or by sending the request
directly to a WINS server
• If the query is sent to a WINS server and the name
can be resolved, the WINS server sends a Name
Query Response to the client computer
• Otherwise the WINS server sends a negative
Name Query Request
Database Replication Between Two
or More WINS Servers
• NetBIOS name registrations in a WINS database are
replicated to other WINS servers by configuring WINS
servers as either push or pull partners
• Push partner – forces their updates on the pull partners
• The push partner informs its pull partner that the WINS
database has changed
• The pull partner then responds with a replication request
• The push partner then sends the new, updated entry to its
pull partner in one of two ways:
– Wait until a predetermined number of WINS updates have been
collected
– Immediately replicate the updated entry