chapter06-170305100744.pdf

Top-Down Network Design Chapter Six Designing Models for Addressing and Naming Copyright 2010 Cisco Press & Priscilla Oppenheimer Guidelines for Addressing and 2 Naming  Use a structured model for addressing and naming  Ass...

Top-Down Network Design Chapter Six Designing Models for Addressing and Naming Copyright 2010 Cisco Press & Priscilla Oppenheimer Guidelines for Addressing and 2 Naming  Use a structured model for addressing and naming  Assign addresses and names hierarchically  Decide in advance if you will use  Central or distributed authority for addressing and naming  Public or private addressing  Static or dynamic addressing and naming  Advantages of Structured 3 Models for Addressing &  Naming It makes it easier to  Read network maps  Operate network management software  Recognize devices in protocol analyzer traces  Meet goals for usability  Design filters on firewalls and routers  Implement route summarization Public IP Addresses 4  Managed by the Internet Assigned Numbers Authority (IANA)  Users are assigned IP addresses by Internet service providers (ISPs).  ISPs obtain allocations of IP addresses from their appropriate Regional Internet Registry (RIR) Regional Internet Registries 5 (RIR)  American Registry for Internet Numbers (ARIN) serves North America and parts of the Caribbean.  RIPE Network Coordination Centre (RIPE NCC) serves Europe, the Middle East, and Central Asia.  Asia-Pacific Network Information Centre (APNIC) serves Asia and the Pacific region.  Latin American and Caribbean Internet Addresses Registry (LACNI serves Latin America and parts of the Caribbean.  African Network Information Centre (AfriNIC) serves Africa. Private Addressing 6 10.0.0.0– 10.255.255.255 172.16.0.0 – 172.31.255.255 192.168.0.0 – 192.168.255.255 Criteria for Using Static Vs. Dynamic 7 Addressing  The number of end systems  The likelihood of needing to renumber  The need for high availability  Security requirements  The importance of tracking addresses  Whether end systems need additional information  (DHCP can provide more than just an address) The Two Parts of an IP Address 8 32 Bits Prefix Host Prefix Length Prefix Length 9  An IP address is accompanied by an indication of the prefix length  Subnet mask  /Length  Examples  192.168.10.1 255.255.255.0  192.168.10.1/24 Subnet Mask 10  32 bits long  Specifies which part of an IP address is the network/subnet field and which part is the host field  The network/subnet portion of the mask is all 1s in binary.  The host portion of the mask is all 0s in binary.  Convert the binary expression back to dotted-decimal notation for entering into configurations.  Alternative  Use slash notation (for example /24)  Specifies the number of 1s Subnet Mask Example 11  11111111 11111111 11111111 00000000  What is this in slash notation?  What is this in dotted-decimal notation? Another Subnet Mask Example 12  11111111 11111111 11110000 00000000  What is this in slash notation?  What is this in dotted-decimal notation? One More Subnet Mask Example 13  11111111 11111111 11111000 00000000  What is this in slash notation?  What is this in dotted-decimal notation? Designing Networks with 14 Subnets  Determining subnet size  Computing subnet mask  Computing IP addresses Addresses to Avoid When 15 Subnetting  A node address of all ones (broadcast)  A node address of all zeros (network)  A subnet address of all ones (all subnets)  A subnet address of all zeros (confusing)  Cisco IOS configuration permits a subnet address of all zeros with the ip subnet-zero command Practice 16  Network is 172.16.0.0  You want to divide the network into subnets.  You will allow 600 nodes per subnet.  What subnet mask should you use?  What is the address of the first node on the first subnet?  What address would this node use to send to all devices on its subnet? More Practice 17  Network is 172.16.0.0  You have eight LANs, each of which will be its own subnet.  What subnet mask should you use?  What is the address of the first node on the first subnet?  What address would this node use to send to all devices on its subnet?  One More 18  Network is 192.168.55.0  You want to divide the network into subnets.  You will have approximately 25 nodes per subnet.  What subnet mask should you use?  What is the address of the last node on the last subnet?  What address would this node use to send to all devices on its subnet? IP Address Classes 19  Classes are now considered obsolete  But you have to learn them because  Everyone in the industry still talks about them!  You may run into a device whose configuration is affected by the classful system Classful IP Addressing 20 Class First First Byte Prefix Intent Few Bits Length A 0 1-126* 8 Very large networks B 10 128-191 16 Large networks C 110 192-223 24 Small networks D 1110 224-239 NA IP multicast E 1111 240-255 NA Experimental *Addresses starting with 127 are reserved for IP traffic local to a host. Division of the Classful Address 21 Space Class Prefix Number of Addresses Length per Network A 8 224-2 = 16,777,214 B 16 216-2 = 65,534 C 24 28-2 = 254 Classful IP is Wasteful 22  Class A uses 50% of address space  Class B uses 25% of address space  Class C uses 12.5% of address space  Class D and E use 12.5% of address space Classless Addressing 23  Prefix/host boundary can be anywhere  Less wasteful  Supports route summarization  Also known as  Aggregation  Supernetting  Classless routing  Classless inter-domain routing (CIDR)  Prefix routing Supernetting 24 172.16.0.0 172.17.0.0 172.18.0.0 Branch-Office Router 172.19.0.0 Enterprise Core Branch-Office Networks Network  Move prefix boundary to the left  Branch office advertises 172.16.0.0/14 172.16.0.0/14 Summarization 25 Second Octet in Decimal Second Octet in Binary 16 00010000 17 00010001 18 00010010 19 00010011 Discontiguous Subnets 26 Area 0 Network 192.168.49.0 Router A Router B Area 1 Area 2 Subnets 10.108.16.0 - Subnets 10.108.32.0 - 10.108.31.0 10.108.47.0 A Mobile Host 27 Router A Router B Subnets 10.108.16.0 - 10.108.31.0 Host 10.108.16.1 IPv6 Aggregatable Global Unicast 28 Address Format 3 13 8 24 16 64 bits FP TLA RES NLA SLA Interface ID ID ID ID Site Public topology Topology  FP Format Prefix (001)  TLA ID Top-Level Aggregation Identifier  RES Reserved for future use  NLA ID Next-Level Aggregation Identifier  SLA ID Site-Level Aggregation Identifier  Interface ID Interface Identifier Upgrading to IPv6 29  Dual stack  Tunneling  Translation Guidelines for Assigning Names 30  Names should be  Short  Meaningful  Unambiguous  Distinct  Case insensitive  Avoid names with unusual characters  Hyphens, underscores, asterisks, and so on  Domain Name System 31 (DNS)  Maps names to IP addresses  Supports hierarchical naming  example: frodo.rivendell.middle-earth.com  A DNS server has a database of resource records (RRs) that maps names to addresses in the server’s “zone of authority”  Client queries server  Uses UDP port 53 for name queries and replies  Uses TCP port 53 for zone transfers  DNS Details 32  Client/server model  Client is configured with the IP address of a DNS server Manually or DHCP can provide the address  DNS resolver software on the client machine sends a query to the DNS server. Client may ask for recursive lookup.  DNS Recursion 33  A DNS server may offer recursion, which allows the server to ask other servers  Each server is configured with the IP address of one or more root DNS servers.  When a DNS server receives a response from another server, it replies to the resolver client software. The server also caches the information for future requests.  The network administrator of the authoritative DNS server for a name defines the length of time that a non-authoritative server may cache information. Summary 34  Use a systematic, structured, top-down approach to addressing and naming  Assign addresses in a hierarchical fashion  Distribute authority for addressing and naming where appropriate  IPv6 looms in our future Review Questions 35  Why is it important to use a structured model for addressing and naming?  When is it appropriate to use IP private addressing versus public addressing?  When is it appropriate to use static versus dynamic addressing?  What are some approaches to upgrading to IPv6?