itec 275 computer networks – switching, routing, and wans

ITEC 275 Computer Networks – Switching, Routing, and

WANs

Week 6Robert 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 summarizationThe 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: Stateful autoconfiguration 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

Prefix Host

32 Bits

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 AddressingOutsourcing 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

• 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

Determinations

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 IntentFew Bits Length

A 0 1-126* 8 Very large networksB 10 128-191 16 Large networksC 110 192-223 24 Small networksD 1110 224-239 NA IP multicastE 1111 240-255 NA Experimental

*Addresses starting with 127 are reserved for IP traffic local to a host.

Class Prefix Number of AddressesLength per Network

A 8 224-2 = 16,777,214B 16 216-2 = 65,534C 24 28-2 = 254

Division of the Classful Address Space

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

• Move prefix boundary to the left• Branch office advertises 172.16.0.0/14

172.16.0.0

172.17.0.0

172.18.0.0

172.19.0.0

Branch-Office NetworksEnterprise Core

Network

Branch-Office Router

Addressing Hierarchy

Figure 6-6 – Page 387

• Summary 192.168.0/21

Route summarization

Figure 6-5 – Page 386

172.16.0.0/14 SummarizationFirst Octet in Decimal First Octet in

binary172 10101100Second Octet in DecimalSecond Octet in

Binary

16 0001000017 0001000118 0001001019 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 1Subnets 10.108.16.0 -

10.108.31.0

Area 0Network

192.168.49.0

Area 2Subnets 10.108.32.0 -

10.108.47.0

Router A Router B

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

Subnets 10.108.16.0 - 10.108.31.0

Router A Router B

Host 10.108.16.1

• 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

• 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

• 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

IPv6 Features (continued)

• The format is x:x:x:x:x:x:x:x, where x is a 16-bit hexadecimal field– 2035:0001:2BC5:0000:0000:087C:0000:000A

• Leading 0s within each set of four hexadecimal digits can be omitted, and a pair of colons (::) can be used, once within an address, to represent any number of successive 0s.– 2035:1:2BC5::87C:0:A

IPv6 Address Format

• Link-local address: The host configures its own link-local address autonomously, using the link-local prefix FE80::0/10 and a 64-bit identifier for the interface, in an EUI-64 format.

• Stateless autoconfiguration: A router on the link advertises—either periodically or at the host's request—network information, such as the 64-bit prefix of the local network and its willingness to function as a default router for the link. Hosts can automatically generate their global IPv6 addresses by using the prefix in these router messages; the hosts do not need manual configuration or the help of a device such as a DHCP server.

• Stateful using DHCP for IPv6 (DHCPv6): DHCPv6 is an updated version of DHCP for IPv4. DHCPv6 gives the network administrator more control than stateless autoconfiguration and can be used to distribute other information, including the address of the DNS server. DHCPv6 can also be used for automatic domain name registration of hosts using a dynamic DNS server. DHCPv6 uses multicast addresses.

IPv6 Addresses

IPv6 Aggregatable Global Unicast Address Format

• 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

3 13 8 24 16 64 bits

FP TLAID

RES NLAID

SLAID

Interface ID

Public topology SiteTopology

Upgrading to IPv6

• Dual stack• Tunneling• Translation

Dual-Stack

A dual-stack node enables both IPv4 and IPv6 stacks. Applications communicate with both IPv4 and IPv6 stacks; the IP version choice is based on name lookup and application preference. This is the most appropriate method for campus and access networks during the transition period, and it is the preferred technique for transitioning to IPv6. A dual-stack approach supports the maximum number of applications.

Figure 6-24

Tunneling

Figure 2-25

Translation

Dual-stack and tunneling techniques manage the interconnection of IPv6 domains. For legacy equipment that will not be upgraded to IPv6 and for some deployment scenarios, techniques are available for connecting IPv4-only nodes to IPv6-only nodes, using translation, an extension of NAT techniques.

Guidelines for Assigning Names• Names should be

– Short– Meaningful– Unambiguous– Distinct– Case insensitive

• Avoid names with unusual characters– Hyphens, underscores, asterisks, and so on

• 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

Domain Name System (DNS)

DNS Details• 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• 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

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 dynamic addressing?

• What are some approaches to upgrading to IPv6?

This Week’s Outcomes

• IP Addressing• Static and Dynamic Assignment• IPv6• IPv4 to IPv6 Transition Methods

Due this week

• 5-1 – Concept questions 4• 1-5-1 – Network design project

– Switches

Next week

• Read chapters 7 in Top-Down Network Design

• 6-1 – Concept questions 5• FranklinLive session 7

Q & A

• Questions, comments, concerns?