Lectures Top-Down Network Design - Chapter 6: Designing Models for Addressing and Naming

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1. Top-Down Network Design, Ch. 6: Designing Models for Addressing and Namin Top-Down Network Design Chapter Six Designing Models for Addressing and Naming Copyright 2010 Cisco Press & Priscilla Oppenheimer Guidelines for Addressing and 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 andid naming – Public or private addressing – Static or dynamic addressing and naming Copyright 2004 Cisco Press & Priscilla Oppenheimer Page 1
2. Top-Down Network Design, Ch. 6: Designing Models for Addressing and Namin Advantages of Structured 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 • Managed by the Internet Assigned Nu mbers Au thority (IANA) • Users are assigned IP addresses by Internet service providers (ISPs). • ISPs obtain allocations of IP addresses from their appropriate Regional Internet Registry (RIR) Copyright 2004 Cisco Press & Priscilla Oppenheimer Page 2
3. Top-Down Network Design, Ch. 6: Designing Models for Addressing and Namin Regional Internet Registries (RIR) • American Registry for Internet Numbers (ARIN) serv es N otorth Am eri caaca an dpatsod parts of th eCabbeae 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 (LACNIC) serves Latin America and parts of the Caribbean. • African Network Information Centre (AfriNIC) serves Africa. Private Addressing • 10.0.0.0 – 10.255.255.255 • 172.16.0.0 – 172.31.255.255 • 192.168.0.0 – 192.168.255.255 Copyright 2004 Cisco Press & Priscilla Oppenheimer Page 3
4. Top-Down Network Design, Ch. 6: Designing Models for Addressing and Namin Criteria for Using Static Vs. Dynamic Addressing • The number of end systems • The like lihoo d o f nee ding to renum ber • 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 32 Bits Prefix Host Prefix Length Copyright 2004 Cisco Press & Priscilla Oppenheimer Page 4
5. Top-Down Network Design, Ch. 6: Designing Models for Addressing and Namin Prefix Length • An IP address is accompanied by an in dica tion o f the pre fix leng th – Subnet mask – /Length •Examples – 192. 168. 10. 1 255. 255. 255. 0 – 192.168.10.1/24 Subnet Mask • 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 Copyright 2004 Cisco Press & Priscilla Oppenheimer Page 5
6. Top-Down Network Design, Ch. 6: Designing Models for Addressing and Namin Subnet Mask Example • 11111111 11111111 11111111 00000000 • What is this in slash notation? • What is this in dotted-decimal notation? Another Subnet Mask Example • 11111111 11111111 11110000 00000000 • What is this in slash notation? • What is this in dotted-decimal notation? Copyright 2004 Cisco Press & Priscilla Oppenheimer Page 6
7. Top-Down Network Design, Ch. 6: Designing Models for Addressing and Namin One More Subnet Mask Example • 11111111 11111111 11111000 00000000 • What is this in slash notation? • What is this in dotted-decimal notation? Designing Networks with Subnets • Determining subnet size • Computing subnet mask • Computing IP addresses Copyright 2004 Cisco Press & Priscilla Oppenheimer Page 7
8. Top-Down Network Design, Ch. 6: Designing Models for Addressing and Namin Addresses to Avoid When 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 confi gurati on permit s a sub net address of all zeros with the ip subnet-zero command Practice • 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? Copyright 2004 Cisco Press & Priscilla Oppenheimer Page 8
9. Top-Down Network Design, Ch. 6: Designing Models for Addressing and Namin More Practice • Network is 172.16.0.0 • You h ave e ig ht LANs, eac h o f w hic h w ill 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 • Network is 192.168.55.0 • YttdiidthtkitbtYou 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? Copyright 2004 Cisco Press & Priscilla Oppenheimer Page 9
10. Top-Down Network Design, Ch. 6: Designing Models for Addressing and Namin IP Address Classes • 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 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. Copyright 2004 Cisco Press & Priscilla Oppenheimer Page 10
11. Top-Down Network Design, Ch. 6: Designing Models for Addressing and Namin Division of the Classful Address Space Class Prefix Number of Addresses Length per Network A8 224-2 = 16,777,214 B16216-2 = 65,534 C2428-2 = 254 Classful IP is Wasteful • 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 Copyright 2004 Cisco Press & Priscilla Oppenheimer Page 11
12. Top-Down Network Design, Ch. 6: Designing Models for Addressing and Namin Classless Addressing • 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 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 Copyright 2004 Cisco Press & Priscilla Oppenheimer Page 12
13. Top-Down Network Design, Ch. 6: Designing Models for Addressing and Namin 172.16.0.0/14 Summarization Second Octet in Decimal Second Octet in Binary 16 00010000 17 00010001 18 00010010 19 00010011 Discontiguous Subnets 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 Copyright 2004 Cisco Press & Priscilla Oppenheimer Page 13
14. Top-Down Network Design, Ch. 6: Designing Models for Addressing and Namin A Mobile Host Router A Router B Subnets 10.108.16.0 - 10.108.31.0 Host 10.108.16.1 IPv6 Aggregatable Global Unicast 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 Copyright 2004 Cisco Press & Priscilla Oppenheimer Page 14
15. Top-Down Network Design, Ch. 6: Designing Models for Addressing and Namin Upgrading to IPv6 • Dual stack • Tunneling • Translation Guidelines for Assigning Names • Names should be – Short – Meaningful – Unambiguous –Distinct – Case insensitive • Avoid names with unusual characters – Hyphens, underscores, asterisks, and so on Copyright 2004 Cisco Press & Priscilla Oppenheimer Page 15
16. Top-Down Network Design, Ch. 6: Designing Models for Addressing and Namin Domain Name System (DNS) • Maps names to IP addresses • Support s hi erarc hica l nam ing – 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 • Client/server model • Client is con figure d w it h t he IP a ddress of a DNS server – Manually or DHCP can provide the address • DNS resolver software on the client machine sen ds a query to the DNS server. Client may ask for recursive lookup. Copyright 2004 Cisco Press & Priscilla Oppenheimer Page 16
17. Top-Down Network Design, Ch. 6: Designing Models for Addressing and Namin DNS Recursion • 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 • 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 Copyright 2004 Cisco Press & Priscilla Oppenheimer Page 17
18. Top-Down Network Design, Ch. 6: Designing Models for Addressing and Namin Review Questions • 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 dyygnamic addressing? • What are some approaches to upgrading to IPv6? Copyright 2004 Cisco Press & Priscilla Oppenheimer Page 18