//S15 IPA and Host Name Resolution
Exam Objectives
1) Diagnosing and resolving IPA problems
2) Diagnosing and resolving name resolution problems
Revise:
• TCP/IP Properties required for troubleshooting [IPA, Subnet mask and default gateway]
• Solving name resolution when only IPA will work, and vice versa
1. Identify symptoms
2. Determine TCP/IP settings - ipconfig /all
3. Determine which TCP/IP component is wrong - ping
4. Determine the best utility
Test Layers in order:
1. TCP/IP Configuration - IPA, Subnet, Gateway, host functioned before? If yes then ...
2. Network Hardware - card and cable, ping 127.0.01, ping local IPA, ping other host
3. IPA - ipconfig
4. Subnet addressing
5. Host Name resolution
6. NetBIOS Name resolution
Independant from eachother (Hardware will not solve DNS) but most likely to go wrong
IPA, Subnet, Gateway, host functioned before? If yes then ...
a) Check card and cable
b) ping 127.0.01 - response m,eans TCP/IP is configured
c) ping local IPA
d) ping other host - fail could be hardware fault (check other machine - network down?)
TCP/IP Initialisation problems:
TCP/IP config correct
Determine if TCP/IP is boud to at least one network adapter
Where
Control Panel->Network->Bindings
ipconfig
Examine infomation relating to failure [Hardware and TCP/IP] i.e. network card not found, or incorrectly incorrectly
During sytem startup, error dialogs, before login, indicate hardware fault. Examine Event viewer for more information
Click on Event->Event Detail dialog
• Computer not able to talk to another host
• Connction hung
• Receiving messages intended for another host
ipconfig - verify IPA, subnet amd gateway
ping, route and tracert - if host is reached and path taken
NT TCP/IP fails if host with same IPA already on network
Gives error message in event viewer (other operating systems do not - that is a LIE!)
Receiving message for another host ( in telnet session, other computers name in banner) => indicates name resolution problem
Incorrect, especially custom masks
Number of name sources, each can introduce an error
• NT uses NetBIOS machine name as default host name
• ping and telnet don't use NetBIOS, use sockets i.e #10.30.32.167(132)
Resolving host name to IPA to time consumming and complex
Even if connection to other hosts is possible, other problems may exist
Message Bad IP Address <hostname> indicates name resolution problem
Solution depends on method used to resolve names:
• DNS - correct DNS IPA specified, ping DNS, correct DNS mapping, Up to date database
• HOSTS - correct mapping, HOSTS in correct directory, up to date
If can connect with hostname but not IPA then host name to IPA mapping problem exists
Just as complex
Uses host name resolution in addition to NetBIOS name resolution
NetBIOS name must be resolved: Can not use IPA as you can with host name resolution.
If possible to ping, but not NetBIOS session then NetBIOS name resolution problem.
Solution depends on method used to resolve names:
• WINS - WINS database contaain entry?;nbtstat at local cache of names resolved to IPA
• LMHOSTS - entry exists; nbtstat at local cache of names resolved to IPA
Determine if computer name is host name or NetBIOS name and will point to correct solution
Sends packets to router
• Must be on same subnet as host
• Think of as a router
• Only used if no entry in local route table
• More than one can specified, first found is used
If possible to ping host on local subnet but not remote then default gateway problem
• route add <network> mask <mask> <router>
• "To get to this network use this router"
• Bind outer subnets to far side of middle
DNS or HOSTS mapping
HOSTS must be in the correct directory
DNS must be available and Correct syntax
//E16 Utilites to trouble shoot IP configuration
Exam Objectives
1) Identify which utility to use in diagnosing IP configuraton problems
2) MS TCP/IP utilites to diagnose IP configuration problems
Revise:
• Know the purpose of each utility
• ping processes
• ipconfig
• telnet
• ftp
• tftp
• rsh
• rexec
• rcp
• lpr
• lpq
• ping
• ARP
• ipconfig
• tracert
• nbtstat
• NETSTAT
• nslookup
• route
• hostname
Not tested on switcvhes, but which utiliy in which situation.
sends echo request packets to destination to verify connectivity
Use to determine if:
• TCP/IP is installed and initialised correctly
• Local host has correct address
• host on local network can be contacted
• host on remote can be contacted
1. IPA loopback 127.0.0.1 - TCP/IP installed and initialised
2. IPA local host
3. IPA other host on local network - local network ok
4. IPA default gateway - router functions
5. IPA far side of router - packets passed to remote network (optional)
6. name remote host - can communicate across router, and name resolution ok
Ping IPA first, then hostname to elimate potential name resolution problemsFollow sequence if IPA ping fails, as connectivity problem exists
Solutions:
• Restart computer after installing TCP/IP
• IPA specified in TCP/IP properties in Network Control panel, or ipconfig command
• Unique IPA and properdefault gateway, if manually configured
• Router is multihomed NT, then enable IP Forwarding
Always compare with another computer, to determine whether network or local host has the problem
ipconfig /all
IPA, Subnet and gateway plus more, for each network adapter (useful for routers)
ipconfig /all output from two different computers on different subnets should have no similarities.
Check for:
• Correct gateway
• Correct subnet mask
• Correct IPA
Traces route packets take, including routers (hops)it passes
Important to dertermine:
• if destination is reached
• last router passed before transmission fails
• time taken between routers
Displays protocol statistics, and current TCP/IP connections
*From when computer booted
Requires parameters (without, provides current protocol connections)
Can modify, add, delete rote entries in route table on local machine
route print prints current routing table.
Shows routes to remote subnets
Subnet connection problems - check with route print if a route to the network exists.
Default Gateway is not used if entry exists in route table
If no route entry, and packets are not arriving at destination, then check the default gateway configuration
//ES V Monitoring, Optimization and Trouble Shooting
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