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Going Large with TCP/IP

Going Large with TCP/IP. Chapter 14. Contents. Describe the function and capabilities of DNS Explain the function and capabilities of DHCP Describe the function and capabilities of WINS Use common TCP/IP utilities to diagnose problems with DNS, DHCP, or WINS. DNS. DNS Organization.

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Going Large with TCP/IP

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  1. Going Large with TCP/IP Chapter 14

  2. Contents • Describe the function and capabilities of DNS • Explain the function and capabilities of DHCP • Describe the function and capabilities of WINS • Use common TCP/IP utilities to diagnose problems with DNS, DHCP, or WINS

  3. DNS

  4. DNS Organization • Domain Name System (DNS) uses an hierarchical name space – an imaginary tree structure of all possible names within a single system • More fully descriptive names that work better in large networks • NetBIOS uses a flat name space – one big list with no grouping • All names must be unique

  5. Hierarchical Name Spaces Same file name but in different directories People Name Space

  6. DNS Tree • Hierarchy of domains and computers organized in a tree structure • All domains connect to the top of the tree – called the root • Individual computer names, called host names, fit into domains • Each domain can have subdomains separated by a period • A DNS tree is similar to a file system with a root directory and folders and subfolders and files

  7. Small DNS Tree

  8. Fully Qualified Domain Name • A complete DNS name is called a Fully Qualified Domain Name (FQDN) • An FQDN includes the host name and all of its domains in order with the root at the far right • For example, Janelle.ABCDEF. • The period at the end stands for root, but since a FQDN always ends with root, the period is usually left off

  9. DNS Domains Two DNS domains Sub domains added

  10. DNS Servers • DNS information is stored on DNS servers • When a system needs to know the IP address of a DNS name, it asks the DNS server configured in its TCP/IP configuration • DNS servers who store information about a domain or set of domains are called the authoritative DNS server for that domain or domains

  11. DNS Root Servers • If your local DNS server is not the authoritative DNS server for the domain you need an IP address in, then your local DNS server will ask the root server • The root server will point your local DNS server to another DNS server that will either have the IP address or know where else to send your local DNS server • Root servers know the IP addresses of only the second-level DNS names – not the IP addresses of hosts further down the tree

  12. The Internet and DNS • The Internet uses DNS with a very specific naming system • First level domain names are .com, .net, .edu, .gov, and so forth • The DNS root for the entire Internet consists of 13 powerful DNS servers scattered all over the world • Actually, there are 13 logical servers that are really many DNS servers acting as one huge DNS server

  13. Hierarchical Name Space • No two machines on the entire Internet may have the same FQDN • However, most web servers are called www • But if you look at their entire name (FQDN), they will be different • For example, www.totalsem.com and www.microsoft.com are both web servers named www but in different domains

  14. DNS Domains

  15. Name Resolution • Browsers like Internet Explorer allow us to type in URLs like www.microsoft.com • Your browser must then resolve the name to an IP address • There are three ways to resolve the name • Broadcasting • Hosts file • DNS server • Browsers will also allow us to just type the IP address instead of the URL • In fact, you wouldn’t even need DNS if you knew the IP address of all the Internet sites you wanted to visit – but do you?

  16. Name Resolution URL using a FQDN Using the IP address

  17. Name Resolution: Broadcasting • There are several ways to resolve names to IP addresses • Broadcasting • The host sends a broadcast message across the entire network saying “Hey, if your name is _____, send me your IP address” • This works fine in small networks, but not larger networks with routers • Routers do not forward broadcasts

  18. Name Resolution Across Routers

  19. Name Resolution: HOSTS File • There are several ways to resolve names to IP addresses • HOSTS file • A file that contains name to IP address mappings 109.54.94.197 stephen.totalsem.com 138.125.163.17 roger.totalsem.com 127.0.0.1 localhost • Notice the name localhost appears as an alias for the loopback address, 127.0.0.1

  20. Name Resolution: DNS

  21. Name Resolution: DNS • No single machine needs to know every DNS name – just who to ask if it doesn’t • DNS is a distributed, decentralized database • An administrator just has to add a new entry once • No single administrator has to maintain the entire database – it is distributed

  22. DNS Cache • Most web browsers and Windows 2000/2003/XP systems keep track of DNS resolutions it has done in memory in the DNS resolver cache • To see the cache in Windows, use the command IPCONFIG /displaydns • To erase the cache, use the command IPCONFIG /flushdns

  23. DNS Resolver Cache

  24. DNS Servers • Many NOSs come with built-in DNS server software • To see the DNS server in Windows 2000 Server, select Administrative Tools | DNS from the Start menu

  25. Cached Lookup • The first folder, Cached Lookup, is where the DNS server keeps track of recently resolved FQDNs • This is where people have browsed lately!

  26. Forward Lookup Zones • The authoritative DNS server keeps the IP addresses in the Forward Lookup Zones folder • The SOA (Start of Authority) record indicates the DNS server’s domain (totalhome) it has authority over • The NS (Name Server) records are all of the DNS servers for the domain (totalhomedc1 & totalhomedc2) • The A (Host) records are the IP addresses and names of all the systems in the domain See the next slide

  27. Forward Zone Lookups

  28. Cache-Only DNS Servers • Cache-only DNS servers do not have forward lookup zones • They only keep track of learned name resolutions in memory • They are not responsible for telling other DNS servers the names of clients

  29. Reverse Lookup Zones • Reverse Lookup Zones allow a DNS server to resolve an IP address to an FQDN • Forward Lookup Zones allow a DNS server to resolve an FQDN to an IP address – just the opposite

  30. Troubleshooting DNS • Most DNS problems are with the client • If it is with the DNS server, you may see a “Server not found” error • First, clear the cache using IPCONFIG /flushdns • Try to ping a website using a FQDN • Try to ping the same website using an IP address • If it works with the IP address but not the FQDN, it’s a DNS problem

  31. Using PING

  32. Troubleshooting DNS • Check your DNS server settings in your TCP/IP properties to make sure they are correct • Check your DNS server information in IPCONFIG /all or WINIPCFG • If this information doesn’t match your TCP/IP settings, then you may need to refresh your DHCP settings (we’ll cover that later in this show)

  33. Troubleshooting DNS • NSLOOKUP allows you to query all types of information about a DNS server and how your system uses it • Run from a command prompt • Use exit to get back to a command prompt • Running NSLOOKUP without any switches shows me the IP address and name of my DNS server • Attach to a server by using server followed by the IP address or domain name C:\>nslookup Default Server: totalhomedc2.totalhome Address: 192.168.4.155 >server totalhomedc1 Default Server: totalhomedc1.totalhome Addresses: 192.168.4.157, 192.168.4.156 >

  34. DHCP

  35. DHCP • Dynamic Host Configuration Protocol (DHCP) automates TCP/IP client configuration • DHCP may offer many TCP/IP settings such as IP address, subnet mask, default gateway, DNS server, WINS servers, and so on • Any client may choose to use DHCP or entries may be statically (manually) entered • Some entries may be obtained through DHCP and others manually entered • DHCP lessens administrative work

  36. Windows 2000 DHCP Program

  37. DHCP Scope • The DHCP scope is a pool of IP addresses that a DHCP server may allocate to clients

  38. Leases • IP information is leased to a client for certain amount of time • 8 days by default for Windows 2000/2003 • Clients try to renew their lease periodically • Address leases are the current leases

  39. DHCP Scope Options • DHCP scope options show some of the TCP/IP information that is leased

  40. Troubleshooting DHCP • DHCP requires little client configuration • If a DHCP server cannot be found, you’ll get an error on reboot like that shown below

  41. APIPA • Any Windows 98 or later client configured for DHCP that cannot access a DHCP server will default to an Automatic Private IP Address (APIPA) starting with 169.254 • This allows your system to talk to other systems on your subnet with APIPA IP addresses • If you think DHCP is a problem, run IPCONFIG or WINIPCFG to see if your system is using a 169.254.x.x IP address • If it is, you need to try to renew your DHCP information

  42. Renewing IP Information • Run IPCONFIG /renew or click the Renew button in WINIPCFG to try to renew your IP settings from the DHCP server • If you can’t reach the DHCP server, you’ll get the following error message – contact the network administrator if this happens

  43. DHCP Setup Errors • If you’re having DHCP server problems, check the DHCP server settings • Incorrect pool of IP addresses defined • Wrong DNS or DHCP server addresses

  44. Release or Renew • Release will release your current TCP/IP bindings from your NIC • Renew will re-establish your TCP/IP bindings to your NIC • In WINIPCFG use the release or renew buttons • With IPCONFIG use • IPCONFIG /release • IPCONFIG /renew • With Linux, turn the NIC off and then back on • IPCONFIG eth0 down • IPCONFIG eth0 up

  45. WINS

  46. WINS • Windows Internet Name Service (WINS) resolves NetBIOS names to IP addresses • WINS is only needed in a pure Windows networks • A NetBIOS system claims its NetBIOS name by broadcasting it to the network • Microsoft had a big investment in NetBIOS when NetBEUI began to loose market share to TCP/IP • So Microsoft had to make NetBIOS work with TCP/IP

  47. WINS

  48. LMHOSTS • An LMHOSTS file resolves NetBIOS names to IP addresses • DNS HOSTS files do the same thing, but the LMHOSTS file is a Microsoft-specific file that does more for Microsoft systems • Most networks use a WINS server instead since it is easier to administer

  49. WINS Server • NetBIOS hosts register their names with a WINS server • This eliminates the need for LMHOSTS broadcast messages and reduces administration tasks • WINS servers • Reduce overhead from broadcasts • Enable NetBIOS name resolution across routers • Remember that routers do not forward broadcasts • Routers may be configured to act as a WINS relay agent to relay broadcasts to the other side of the router • WINS is needed in large or router networks that still run NetBIOS • Networks with Windows NT and 9x systems

  50. WINS Server

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