ITEC 275 Computer Networks – Switching, Routing, and WANs Week 6 Robert D’Andrea Some slides provide by Priscilla Oppenheimer and used with permission
Agenda • Learning Activities • IP Addressing • Static and Dynamic Assignment • IPv6 • IPv4 to IPv6 Transition Methods
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 and naming • Public or private addressing • Static or dynamic addressing and naming
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 The Structured Model for addressing provids IP addresses with meaning, hierarchical, and planned.
Public IP Addresses • 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) Internet Assigned Numbers Authority (IANA). IANA allocates IP addresses to the Regional Internet Registries (RIRs)
Regional Internet Registries (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 (LACNIC) serves Latin America and parts of the Caribbean. • African Network Information Centre (AfriNIC) serves Africa.
Criteria for Using Static Vs. Dynamic 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)
Criteria for Using Static Vs. Dynamic Addressing • IPv6 Dynamic addressing supports both static and dynamic addressing -Dynamic addressing is referred to as autoconfiguration Part 1: Statefulautoconfiguration method, hosts retrieve addresses and other information from a server set up with a database.
Criteria for Using Static Vs. Dynamic Addressing Part 2: Stateless autoconfiguration method, a hosts generates it’s own address using locally available information. This includes advertised information from routers. The process starts by generating a link-local address for an interface. This involves combining the well-known link- local prefix (FE80::/10) with a 64 bit interface identifier.
The Two Parts of an IP Address 32 Bits Prefix Host Prefix Length
Prefix Length • 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 • 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 • 11111111 11111111 11111111 00000000 • What is this in slash notation? • What is this in dotted-decimal notation?
Subnet Mask Example • 11111111 11111111 11111111 00000000 • What is this in slash notation? • /24 • What is this in dotted-decimal notation? • 255.255.255.0
Another Subnet Mask Example • 11111111 11111111 11110000 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? • /20 • What is this in dotted-decimal notation? • 255.255.240.0
One More Subnet Mask Example • 11111111 11111111 11111000 00000000 • What is this in slash notation? • What is this in dotted-decimal notation?
One More Subnet Mask Example • 11111111 11111111 11111000 00000000 • What is this in slash notation? • 21 • What is this in dotted-decimal notation? • 255.255.248.0
Private and Public Addresses Figure 6-1
Network Address Translation (NAT) • Static • One private address to one public address • Used for servers that must be visible to the public network • Dynamic • Many unregistered addresses to one registered address from a pool of addresses • Used for workstations that only connect to the public network when required • Combination • Used by most organizations
Network Address Translation (NAT) • Problem with Private Addressing Outsourcing network management responsibilities to an outside vendor. With private addressing, the internal networks are not advertised to the outside. NAT problems would occur handling network management protocols like Simple Network Management Protocol (SNMP).
Address use in the Enterprise Figure 6-3
Designing Networks with Subnets • Determining subnet size • Computing subnet mask • Computing IP addresses
Determinations • How many locations? • How many segments are required? • How many devices? • How large must each segment be? • What are the IP addressing requirements for each location? • Is public access required? • What subnet size is appropriate? • Determined by first and second questions
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 configuration permits a subnet address of all zeros with the ip subnet-zero command
IP Subnet-Zero • Under old IP subnetting rules, the all 0’s subnet was reserved for the network, and the all 1’s subnet was reserved for the broadcast. Over time, engineers found that the all 0’s subnet wasn’t really used and, if it could be handed out as a useable network, many IP addresses could be changed.
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?
Practice • Network is 172.16.0.0 • You want to divide the network into subnets. • 64 • You will allow 600 nodes per subnet. • 1022 • What subnet mask should you use? • 255.255.252.0 (/22) • What is the address of the first node on the first subnet? • 172.16.0.1 • What address would this node use to send to all devices on its subnet? • 172.16.3.255
More Practice • 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?
More Practice • Network is 172.16.0.0 • You have eight LANs, each of which will be its own subnet. • What subnet mask should you use? • 255.255.224.0 (/19) • What is the address of the first node on the first subnet? • 172.16.0.1 • What address would this node use to send to all devices on its subnet? • 172.16.31.255
One More • 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?
One More • Network is 192.168.55.0 • You want to divide the network into subnets. • 8 • You will have approximately 25 nodes per subnet. • 30 • What subnet mask should you use? • 255.255.255.224 (/27) • What is the address of the last node on the last subnet? • 192.168.255.254 • What address would this node use to send to all devices on its subnet? • 192.168.255.255
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
IP Address Classes • Traditional routing, is known as classful routing. No information is transmitted about the prefix length. The hosts and router examine the first three bits of the IP address to determine its class. • CIDR notation identifies the prefix length with a length field, followed by a slash. Example: 10.1.0.1/16 The prefix length is 16 bits long. The subnet mask is 255.255.0.0.
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.
Division of the Classful Address 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 • 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 • 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
Classless Addressing • Classless routing protocols transmit a prefix length with the IP address. This allows classless routing protocols to group networks into one entry and use the prefix length to specify which networks are grouped. • Classless routing protocols include RIPv2, EIGRP, OSPF, BGP, and IS-IS.
Supernetting 172.16.0.0 • Move prefix boundary to the left • Branch office advertises 172.16.0.0/14 172.17.0.0 172.18.0.0 Branch-Office Router 172.19.0.0 Enterprise Core Network Branch-Office Networks
Addressing Hierarchy Figure 6-6 – Page 387
Route summarization • Summary 192.168.0/21 Figure 6-5 – Page 386
172.16.0.0/14 Summarization First Octet in Decimal First Octet in binary 172 10101100 Second Octet in Decimal Second Octet in Binary 16 00010000 17 00010001 18 00010010 19 00010011
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
Discontiguous Subnets Area 0 Network 192.168.49.0 Router A Router B Area 1 Subnets 10.108.16.0 - 10.108.31.0 Area 2 Subnets 10.108.32.0 - 10.108.47.0
A Mobile Host • Mobile Host is a host that moves from one network to another and has a statically defined IP address. The administrator can move a mobile host to another and configure a router with a host-specific route to specify that traffic for the host should be routed through that router. Classless routing protocols match the longest prefix. Example: 10.108.16.0/20 and 10.108.16.1/32
A Mobile Host Router A Router B Subnets 10.108.16.0 - 10.108.31.0 Host 10.108.16.1
IPv6 • A technology developed to overcome the limitations of the current standard, IPv4 • Combines expanded addressing with a more efficient and feature-rich header to improve scaling • Satisfies the increasingly complex requirements of hierarchical addressing that IPv4 does not support
IPv6 Features • Larger address space: • IPv6 addresses are 128 bits, compared to IPv4's 32 bits • Allows more support for addressing hierarchy levels • A much greater number of addressable nodes • Simpler auto-configuration of addresses • Globally unique IP addresses: • Every node can have a unique global IPv6 address • Eliminates the need for NAT. • Site multi-homing: • IPv6 allows hosts to have multiple IPv6 addresses • Allows networks to have multiple IPv6 prefixes • Sites can have connections to multiple ISPs without breaking the global routing table
IPv6 Features (continued) • Header format efficiency: • A simplified header with a fixed header size makes processing more efficient. • Improved privacy and security: • IPsec is the IETF standard for IP network security, available for both IPv4 and IPv6. Although the functions are essentially identical in both environments, IPsec is mandatory in IPv6. IPv6 also has optional security headers. • Flow labeling capability: • A new capability enables the labeling of packets belonging to particular traffic flows for which the sender requests special handling, such as nondefault quality of service (QoS) or real-time service. • Increased mobility and multicast capabilities: • Mobile IPv6 allows an IPv6 node to change its location on an IPv6 network and still maintain its existing connections. With Mobile IPv6, the mobile node is always reachable through one permanent address. A connection is established with a specific permanent address assigned to the mobile node, and the node remains connected no matter how many times it changes locations and addresses