Week Nine

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

3. Week Eight Topics • NAT Overload • CIDR • Classful and classful • IPv6 Standard • IPv6 Transition • 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 aren’t 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 Classfulrouting 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 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.

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 x:x:x:x:x:x:x:x,where x is a 16-bit hexadecimal field Leading zeros in a field are optional: 2031:0:130F:0:0:9C0:876A:130B Successive fields of 0 can be represented as ::, but only once per address. Examples: 2031:0000:130F:0000:0000:09C0:876A:130B 2031:0:130f::9c0:876a:130b FF01:0:0:0:0:0:0:1 >>> FF01::1 0:0:0:0:0:0:0:1 >>> ::1 0:0:0:0:0:0:0:0 >>> ::

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 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.

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 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

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.