Week Nine• Attendance• Announcements• Review Week Eight Information• Current Week Information• Upcoming Assignments

Week Eight Topics1. NAT Overload2. CIDR3. Classful and classful4. IPv6 Standard5. IPv6 Transition6. Routing Protocols

Network Address Translation (NAT)What is NAT Overload?

NAT overloading (sometimes called Port Address Translation or PAT) maps multiple private IP addresses to a single public IP address or a few addresses. This is what most home routers do. With NAT overloading, multiple addresses can be mapped to one or to a few addresses because each private address is also tracked by a port number. When a client opens a TCP/IP session, the NAT router assigns a port number to its source address. NAT overload ensures that clients use a different TCP port number for each client session with a server on the Interne

NAT Terminology

Classless Interdomain Routing (CIDR)What is CIDR?

CIDR is a new addressing scheme for the Internet which allows for more efficient allocation of IP addresses than the old Class A, B, and C address scheme.

Why Do We Need CIDR?With a new network being connected to the Internet every 30 minutes the Internet was faced with two critical problems:

Running out of IP addressesRunning out of capacity in the global

routing tables

Classless Interdomain Routing (CIDR)CIDR is pronounced “cider”With CIDR, addresses use bit identifiers, or bit masks, instead of an address class to determine the network portion of an address CIDR uses the /N notation instead of subnet masksCIDR allows for the more efficient allocation of IP addresses

Classless Interdomain Routing (CIDR)

172.16.0.0 255.255.0.0= 172.16.0.0 /16

198.30.1.0 255.255.255.0= 198.30.1.0 /24

Note that 192.168.24.0 /22 is not a Class C network, it has a subnet mask of 255.255.252.0

CIDR and Route Aggregation• CIDR allows routers to summarize, or

aggregate, routing information• One address with a mask can represent

multiple networks• This reduces the size of routing tables• Supernetting is another term for route

aggregation

CIDR and Route AggregationGiven four Class C Networks (/24):

192.168.16.0 11000000 1010100000010000 00000000192.168.17.0 11000000 1010100000010001 00000000192.168.18.0 11000000 1010100000010010 00000000192.168.19.0 11000000 1010100000010011 00000000

Identify which bits all these networks have in common. 192.168.16.0 /22 can represent all these networks. The router will look at the first 22 bits of the address to make a routing decision. Note that 192.168.16.0 /22 is not a Class C network, it has a subnet mask of 255.255.252.0

Route Summarization

Importance of Hierarchical Addressing

With summarization, small changes in the network aren’t propagated (spread) throughout the entire network

Benefits of Summarization

Subnet Masks

• A major network is a Class A, B, or C network• Fixed-Length Subnet Masking (FLSM) is

when all subnet masks in a major network must be the same

• Variable-Length Subnet Masking (VLSM) is when subnet masks within a major network can be different.

• Some routing protocols require FLSM; others allow VLSM

VLSM

• VLSM makes it possible to subnet with different subnet masks and therefore results in more efficient address space allocation.

• VLSM also provides a greater capability to perform route summarization, because it allows more hierarchical levels within an addressing plan.

• VLSM requires prefix length information to be explicitly sent with each address advertised in a routing update

VLSM

Classful and Classless Routing Protocols• Classful routing protocols DO NOT send subnet

mask information in their routing updates• When a router receives a routing update, it simply

assumes the default subnet mask (Class A, B, or C)

• VLSM cannot be used in networks that use Classful routing protocols

• Classless routing protocols send the subnet mask (prefix length) in their updates

• VLSM can be used with Classless routing protocols

IPv6 Standard• Larger address space: IPv6 addresses are 128 bits, compared

to IPv4’s 32 bits. This larger addressing space allows more support for addressing hierarchy levels, a much greater number of addressable nodes, and simpler auto configuration of addresses.

• Globally unique IP addresses: Every node can have a unique global IPv6 address, which eliminates the need for NAT.

• Site multi-homing: IPv6 allows hosts to have multiple IPv6 addresses and allows networks to have multiple IPv6 prefixes. Consequently, sites can have connections to multiple ISPs without breaking the global routing table.

• Header format efficiency: A simplified header with a fixed header size makes processing more efficient.

IPv6 Standard• 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 non default quality of service (QoS) or real-time service.

IPv6 Standard• 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.

• Improved global reach ability and flexibility.• Better aggregation of IP prefixes announced in

routing tables.

IPv6 Standard• Multi-homed hosts. Multi-homing is a technique to increase

the reliability of the Internet connection of an IP network. With IPv6, a host can have multiple IP addresses over one physical upstream link. For example, a host can connect to several ISPs.

• Auto-configuration that can include Data Link layer addresses in the address space.

• More plug-and-play options for more devices.• Public-to-private, end-to-end readdressing without address

translation. This makes peer-to-peer (P2P) networking more functional and easier to deploy.

• Simplified mechanisms for address renumbering and modification.

IPv6 Standard

• Better routing efficiency for performance and forwarding-rate scalability

• No broadcasts and thus no potential threat of broadcast storms

• No requirement for processing checksums• Simplified and more efficient extension header

mechanisms• Flow labels for per-flow processing with no

need to open the transport inner packet to identify the various traffic flows

IPv6 StandardMovement to change from IPv4 to IPv6 has already begun, particularly in Europe, Japan, and the Asia-Pacific region.

• These areas are exhausting their allotted IPv4 addresses, which makes IPv6 all the more attractive and necessary.

• In 2002, the European Community IPv6 Task Force forged a strategic alliance to foster IPv6 adoption worldwide.

• The North American IPv6 Task Force has set out to engage the North American markets to adopt IPv6.

• The first significant North American advances are coming from the U.S. Department of Defense (DoD).

IPv6 Standard• Using the "::" notation greatly reduces the size of

most addresses as shown. An address parser identifies the number of missing zeros by separating any two parts of an address and entering 0s until the 128 bits are complete

IPv6 Larger address SpaceIPv4

32 bits or 4 bytes long4,200,000,000 possible addressable nodes

IPv6128 bits or 16 bytes: four times the bits of IPv43.4 * 1038possible addressable nodes340,282,366,920,938,463,374,607,432,768,211,4565 * 1028addresses per person

IPv6 Larger Address Space

IPv6 Representationx:x:x:x:x:x:x:x,where x is a 16-bit hexadecimal fieldLeading zeros in a field are optional:2031:0:130F:0:0:9C0:876A:130BSuccessive fields of 0 can be represented as ::, but only once per address.

Examples:2031:0000:130F:0000:0000:09C0:876A:130B2031:0:130f::9c0:876a:130bFF01:0:0:0:0:0:0:1 >>> FF01::10:0:0:0:0:0:0:1 >>> ::10:0:0:0:0:0:0:0 >>> ::

IPv6 Addressing ModelAddresses are assigned to interfaces

Change from IPv4 mode:Interface “expected” to have multiple addressesAddresses have scope

Link LocalUnique LocalGlobal

Addresses have lifetimeValid and preferred lifetime

IPv6 Address TypesUnicast

Address is for a single interface.IPv6 has several types (for example, global and IPv4 mapped).

MulticastOne-to-manyEnables more efficient use of the networkUses a larger address range

AnycastOne-to-nearest(allocated from unicast address space).Multiple devices share the same address.All anycast nodes should provide uniform service.Source devices send packets to anycast address.Routers decide on closest device to reach that destination.Suitable for load balancing and content delivery services.

IPv6 Global Unicast Addresses• The global unicast and the anycast share the same address

format.• Uses a global routing prefix—a structure that enables

aggregation upward, eventually to the ISP.• A single interface may be assigned multiple addresses of any

type (unicast, anycast, multicast).• Every IPv6-enabled interface must contain at least one

loopback (::1/128)and one link-local address.• Optionally, every interface can have multiple unique local and

global addresses.• Anycast address is a global unicast address assigned to a set of

interfaces (typically on different nodes).• IPv6 anycast is used for a network multihomed to several ISPs

that have multiple connections to each other.

IPv6 Transition Strategies

• The transition from IPv4 does not require upgrades on all nodes at the same time. Many transition mechanisms enable smooth integration of IPv4 and IPv6. Other mechanisms that allow IPv4 nodes to communicate with IPv6 nodes are available. Different situations demand different strategies. The figure illustrates the richness of available transition strategies.

• Recall the advice: "Dual stack where you can, tunnel where you must." These two methods are the most common techniques to transition from IPv4 to IPv6.

IPv6 Transition StrategiesDual stacking is an integration method in which a node has implementation and connectivity to both an IPv4 and IPv6 network. This is the recommended option and involves running IPv4 and IPv6 at the same time. Router and switches are configured to support both protocols, with IPv6 being the preferred protocol.

IPv6 Transition Strategies• Tunneling

The second major transition technique is tunneling. There are several tunneling techniques available, including:Manual IPv6-over-IPv4 tunneling -An IPv6 packet is encapsulated within the IPv4 protocol. This method requires dual-stack routers.Dynamic 6to4 tunneling -Automatically establishes the connection of IPv6 islands through an IPv4 network, typically the Internet. It dynamically applies a valid, unique IPv6 prefix to each IPv6 island, which enables the fast deployment of IPv6 in a corporate network without address retrieval from the ISPs or registries

IPv6 Standard

IPv6 Dual Stacking

Routing Protocols

• One of the primary jobs of a router is to determine the best path to a given destination

• A router learns paths, or routes, from the static configuration entered by an administrator or dynamically from other routers, through routing protocols

Routing Table Structure• Routing Table Principles

3 principles regarding routing tables: Every router makes its decisions alone, based

on the information it has in its routing table.Different routing table may contain different informationA routing table can tell how to get to a

destination but not how to get back (Asymmetric Routing)

Routing information about a path from one network to another does not provide routing information about the reverse, or return, path.

Routing Table Structure• PC1 sends ping to PC2• R1 has a route to PC2’s network• R2 has a route to PC2’s network• R3 is directly connected to PC2’s network

• PC2 sends a reply ping to PC1• R3 has a route to PC1’s network• R2 does not have a route to PC1’s network• R2 drops the ping reply

Routing Table Structure

Routing Tables• Routers keep a routing table in RAM

• A routing table is a list of the best known available routes

• Routers use this table to make decisions about how to forward a packet

• On a Cisco router the show IP route command is used to view the TCP/IP routing table

Routing Table

Routing Table• A routing table maps network prefixes to an

outbound interface.

• When RTA receives a packet destined for 192.168.4.46, it looks for the prefix 192.168.4.0/24 in the routing table

• RTA then forwards the packet out an interface, such as Ethernet0, as directed in the routing table

Routing Loops• A network problem in which packets continue to be

routed in an endless circle

• It is caused by a router or line failure, and the notification of the downed link has not yet reached all the other routers

• It can also occur over time due to normal growth or when networks are merged together

• Routing protocols utilize various techniques to lessen the chance of a routing loop

Routing Table Structure

• The primary function of a router is to forward a packet toward its destination network, which is the destination IP address of the packet.

• To do this, a router needs to search the routing information stored in its routing table.

Routing Protocols• Routing Table is stored in ram and contains information:

• Directly connected networks-this occurs when a device is connected to another router interface

• Remotely connected networks-this is a network that is not directly connected to a particular router network/next hop associations-about the networks include source of information, network address & subnet mask, and Ip address of next-hop router

• The show ip route command is used to view a routing table on a Cisco router

Routing Protocols

Routing Protocols

• Directly Connected Routes-To visit a neighbor, you only have to go down the street on which you already live. This path is similar to a directly-connected route because the "destination" is available directly through your "connected interface," the street.

Static Routing

• Static Routes-A train uses the same railroad tracks every time for a specified route. This path is similar to a static route because the path to the destination is always the same.

Static Routing

• When network only consists of a few routers

• Using a dynamic routing protocol in such a case does not present any substantial benefit.

• Network is connected to internet only through one ISP

• There is no need to use a dynamic routing protocol across this link because the ISP represents the only exit point to the Internet

Static Routing• Hub & spoke topology is used on a large network

• A hub-and-spoke topology consists of a central location (the hub) and multiple branch locations (spokes), with each spoke having only one connection to the hub.

• Using dynamic routing would be unnecessary because each branch has only one path to a given destination-through the central location.

• Static routing is useful in networks that have a single path to any destination network.

Static Routing

• Static routes in the routing table• Includes: network address and subnet mask

and IP address of next hop router or exit interface

• Denoted with the code S in the routing table• Routing tables must contain directly connected

networks used to connect remote networks before static or dynamic routing can be used

Static Routing

Static Routing

Static Routing

• When an interface goes down, all static routes mapped to that interface are removed from the IP routing table

• Static routing is not suitable for large, complex networks that include redundant links, multiple protocols, and meshed topologies

• Routers in complex networks must adapt to topology changes quickly and select the best route from multiple candidates

Static Route Example

The corporate network router has only one path to the network 172.24.4.0 connected to RTY

A static route is entered on RTZ

Routing Protocols

• Dynamic Routes-When driving a car, you can "dynamically" choose a different path based on traffic, weather, or other conditions. This path is similar to a dynamic route because you can choose a new path at many different points on your way to the destination.

Dynamic Routing• Dynamic routing protocols• Are used to add remote networks to a routing

table• Are used to discover networks• Are used to update and maintain routing tables

Dynamic Routing• Automatic network discovery

• Network discovery is the ability of a routing protocol to share information about the networks that it knows about with other routers that are also using the same routing protocol.

• Instead of configuring static routes to remote networks on every router, a dynamic routing protocol allows the routers to automatically learn about these networks from other routers.

• These networks -and the best path to each network -are added to the router's routing table and denoted as a network learned by a specific dynamic routing protocol.

Dynamic Routing• Maintaining routing tables• Dynamic routing protocols are used to share

routing information with other router & to maintain and up date their own routing table.

• Dynamic routing protocols not only make a best path determination to various networks, they will also determine a new best path if the initial path becomes unusable (or if the topology changes)

Dynamic Routing

Routing Protocols

Configuring Dynamic Routing• Dynamic routing of TCP/IP can be implemented using one or

more protocols which are often grouped according to where they are used.

• Routing protocols designed to work inside an autonomous system are categorized as interior gateway protocols (IGPs).

• Protocols that work between autonomous systems are classified as exterior gateway protocols (EGPs).

• Protocols can be further categorized as either distance vector or link-state routing protocols, depending on their method of operation.

Interior Versus Exterior Routing Protocols

An interior gateway protocol (IGP) is a routing protocol that is used within an autonomous system (AS). Two types of IGP.

Distance-vector routing protocols each router does not possess information about the full network topology. It advertises its distances to other routers and receives similar advertisements from other routers. Using these routing advertisements each router populates its routing table. In the next advertisement cycle, a router advertises updated information from its routing table. This process continues until the routing tables of each router converge to stable values.

Interior Versus Exterior Routing Protocols

Distance-vector routing protocols make routing decisions based on hop-by-hop . A distance vector router’s understanding of the network is based on its neighbors definition of the topology, which could be referred to as routing by rumor.

Route flapping is caused by pathological conditions (hardware errors, software errors, configuration errors, intermittent errors in communications links, unreliable connections, etc.) within the network which cause certain reach ability information to be repeatedly advertised and withdrawn.

Interior Versus Exterior Routing ProtocolsIn networks with distance vector routing protocols flapping routes can trigger routing updates with every state change. Cisco trigger updates are sent when these state changes occur. Traditionally, distance vector protocols do not send triggered updates.

Interior Versus Exterior Routing Protocols

Link-state routing protocols, each node possesses information about the complete network topology. Each node then independently calculates the best next hop from it for every possible destination in the network using local information of the topology. The collection of best next hops forms the routing table for the node.This contrasts with distance-vector routing protocols, which work by having each node share its routing table with its neighbors. In a link-state protocol, the only information passed between the nodes is information used to construct the connectivity maps.

Routing Protocols

• Interior routing protocols are designed for use in a network that is controlled by a single organization

• RIPv1 RIPv2, EIGRP, OSPF and IS-IS are all Interior Gateway Protocols

Link State Analogy• Each router has a map of the network

• However, each router looks at itself as the center of the topology

• Compare this to a “you are here” map at the mall

• The map is the same, but the perspective depends on where you are at the time You

Link State Analogy

Exterior Gateway Routing ProtocolAn exterior routing protocol is designed for use between

different networks that are under the control of different organizations

• An exterior routing routes traffic between autonomous systems

• These are typically used between ISPs or between a company and an ISP

• BGPv4is the Exterior Gateway Protocol used by all ISPs on the Internet

EGI and EGP Routing Protocol

IGP and EGP Routing Protocol

Distant Vector Link StateRIP (v1 and v2) OSPFEIGRP (hybrid) IS-IS

Routing ProtocolsEIGRP is an advanced distance vector protocol that employs the best features of link-state routing.

What is Convergence

• Routers share information with each other, but must individually recalculate their own routing tables

• For individual routing tables to be accurate, all routers must have a common view of the network topology

• When all routers in a network agree on the topology they are considered to have converged

Why is Quick Convergence Important?

• When routers are in the process of convergence, the network is susceptible to routing problems because some routers learn that a link is down while others incorrectly believe that the link is still up

• It is virtually impossible for all routers in a network to simultaneously detect a topology change.

Convergence Issues

• Factors affecting the convergence time include the following:

• Routing protocol used • Distance of the router, or the number of hops from

the point of change • Number of routers in the network that use dynamic

routing protocols • Bandwidth and traffic load on communications links • Load on the router • Traffic patterns in relation to the topology change

Routing Protocols• An AS is a group of routers that share similar

routing policies and operate within a single administrative domain.

• An AS can be a collection of routers running a single IGP, or it can be a collection of routers running different protocols all belonging to one organization.

• In either case, the outside world views the entire Autonomous System as a single entity.

Routing Protocols• AS Numbers• Each AS has an identifying number that is assigned by an

Internet registry or a service provider. • This number is between 1 and 65,535. • AS numbers within the range of 64,512 through 65,535are

reserved for privateuse. • This is similar to RFC 1918 IP addresses.

• Because of the finite number of available AS numbers, an organization must present justification of its need before it will be assigned an AS number.

• An organization will usually be a part of the AS of their ISP

Routing Protocols

Routing Protocols

• Each AS has its own set of rules and policies.• The AS number uniquely distinguish it from

other ASs around the world.

Upcoming Deadlines• Assignement 8-2, Concept Questions 6 is due

June 21.• Assignment 1-4-2 Network Design Project

Phase 2: WAN Network Design is due June 21 • Assignement 10-1 Concept Questions 7 is due

July 5