Week Nine

1
(No Transcript)
2
Week Nine

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

3
Week Eight Topics

1. NAT Overload
2. CIDR
3. Classful and classful
4. IPv6 Standard
5. IPv6 Transition
6. Routing Protocols

4
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

5
NAT Terminology
6
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 addresses
• Running out of capacity in the global routing
  tables

7
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
  masks
• CIDR allows for the more efficient allocation of
  IP addresses

8
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

9
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

10
CIDR and Route Aggregation

• Given four Class C Networks (/24)
• 192.168.16.0 11000000 1010100000010000 00000000
• 192.168.17.0 11000000 1010100000010001 00000000
• 192.168.18.0 11000000 1010100000010010 00000000
• 192.168.19.0 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

11
Route Summarization
12
Importance of Hierarchical Addressing

• With summarization, small changes in the network
  arent propagated (spread) throughout the entire
  network

13
Benefits of Summarization
14
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

15
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

16
VLSM
17
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

18
IPv6 Standard

• Larger address space IPv6 addresses are 128
  bits, compared to IPv4s 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.

19
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.

20
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.

21
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.

22
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

23
IPv6 Standard

• Movement 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).
  

24
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

25
IPv6 Larger address Space

• IPv4
• 32 bits or 4 bytes long
• 4,200,000,000 possible addressable nodes
• IPv6
• 128 bits or 16 bytes four times the bits of
  IPv4
• 3.4 1038possible addressable nodes
• 340,282,366,920,938,463,374,607,432,768,211,456
• 5 1028addresses per person

26
IPv6 Larger Address Space
27
IPv6 Representation

• xxxxxxxx,where x is a 16-bit hexadecimal
  field
• Leading zeros in a field are optional
• 20310130F009C0876A130B
• Successive fields of 0 can be represented as ,
  but only once per address.
• Examples
• 20310000130F0000000009C0876A130B
• 20310130f9c0876a130b
• FF010000001 gtgtgt FF011
• 00000001 gtgtgt 1
• 00000000 gtgtgt

28
IPv6 Addressing Model

• Addresses are assigned to interfaces
• Change from IPv4 mode
• Interface expected to have multiple addresses
• Addresses have scope
• Link Local
• Unique Local
• Global
• Addresses have lifetime
• Valid and preferred lifetime

29
IPv6 Address Types

• Unicast
• Address is for a single interface.
• IPv6 has several types (for example, global and
  IPv4 mapped).
• Multicast
• One-to-many
• Enables more efficient use of the network
• Uses a larger address range
• Anycast
• One-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.

30
IPv6 Global Unicast Addresses

• The global unicast and the anycast share the same
  address format.
• Uses a global routing prefixa 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.

31
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.

32
IPv6 Transition Strategies

• Dual 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.

33
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

34
IPv6 Standard
35
IPv6 Dual Stacking
36
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

37
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
  information
• A 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.

38
Routing Table Structure

• PC1 sends ping to PC2
• R1 has a route to PC2s network
• R2 has a route to PC2s network
• R3 is directly connected to PC2s network
• PC2 sends a reply ping to PC1
• R3 has a route to PC1s network
• R2 does not have a route to PC1s network
• R2 drops the ping reply

39
Routing Table Structure
40
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

41
Routing Table
42
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

43
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

44
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.

45
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

46
Routing Protocols
47
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.

48
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.

49
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

50
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.

51
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

52
Static Routing
53
Static Routing
54
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

55
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
56
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.

57
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

58
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.

59
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)

60
Dynamic Routing
61
Routing Protocols
62
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.

63
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.

64
Interior Versus Exterior Routing Protocols

• Distance-vector routing protocols make routing
  decisions based on hop-by-hop . A distance
  vector routers 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.

65
Interior Versus Exterior Routing Protocols

• In 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.

66
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.

67
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

68
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

69
Link State Analogy
70
Exterior Gateway Routing Protocol

• An 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

71
EGI and EGP Routing Protocol
72
IGP and EGP Routing Protocol

• Distant Vector Link State
• RIP (v1 and v2) OSPF
• EIGRP (hybrid) IS-IS

73
Routing Protocols
EIGRP is an advanced distance vector protocol
that employs the best features of link-state
routing.
74
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

75
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.

76
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

77
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.

78
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

79
Routing Protocols
80
Routing Protocols

• Each AS has its own set of rules and policies.
• The AS number uniquely distinguish it from other
  ASs around the world.

81
Upcoming Deadlines

• Assignement 8-2, Concept Questions 6 is due June
  21.
• Assignment 1-4-2 Network Design ProjectPhase 2
  WAN Network Design is due June 21
• Assignement 10-1 Concept Questions 7 is due July
  5