Presentation on theme: "Brief History of the Internet ARPA (Advanced Research Project Agency) – agency of the department of Defense. In the 1960s funded universities and organizations."— Presentation transcript:
Brief History of the Internet ARPA (Advanced Research Project Agency) – agency of the department of Defense. In the 1960s funded universities and organizations to research the development of communication systems. Let to the development of ARPANET – an experimental network that connected computer using packet switching. Evolved in the Internet (capital I). http://www.computerhistory.org/internet_history http://www.computerhistory.org/internet_history
Section 19.1 – Logical addressing IP address is a 32-bit number usually written in the form w.x.y.z. For example, 126.96.36.199. There are 128-bit address (IPv6) but we’ll defer those until later. nslookup can be used to determine the address. Also dig, host, named on Linux Example: nslookup www.uwgb.edu or nslookup www.google.comwww.uwgb.edu
Devices have a physical address (Ethernet) and an IP address (logical address). Command ipconfig /all (PC command prompt) Your IP address is given to you by your ISP and can change; Network card determines the physical address. Won’t change unless you install a new card.
An IP address consists of a Netid and Hostid Ex: Each campus computer has IP address 143.200.x.y 143.200 is the network number. x.y determined the device. Advantage: Routers outside the campus network need only know in which direction 143.200 is located rather than tracking every possible machine. Once on campus, then the specific machine is identified.
Address classes for the early Internet x’s define the Netid y’s define the Hostid Class A: 0xxxxxxx.yyyyyyyy.yyyyyyyy.yyyyyyyy Class B: 10xxxxxx.xxxxxxxx.yyyyyyyy.yyyyyyyy Class C: 110xxxxx.xxxxxxxx.xxxxxxxx.yyyyyyyy Class D: 1110……multicast address…………….. Class determined by the first few bits Multicast (class D) identifies a group of hosts Unicast identifies one (Class A, B, C) 143.200 is a class B address since 143 10 =1000 1111 2
Table 19.1 Number of blocks and block size in classful IPv4 addressing NOTE: Block means number of networks (globally) Block size is the number of hosts (devices) in a network
Classless addressing Classful addressing too coarse for today’s needs. Need more flexibility than just class A, B, or C addresses. An organization needing 5000 addresses (way too large for a class C network) would be a class B network with ~65000 addresses. Most would go unused.
Internet uses Classless Interdomain Routing (CIDR) Left most n bits define the Netid, rightmost n-32 bits define the hostid. Question: how does a router extract the Netid for forwarding?
Address mask Collection of contiguous 1s followed by contiguous 0s 1’s identify bits in the Netid; 0s the hostid Alternative way to identify the Netid Table 19.2 Default masks for classful addressing
In general the notation x.y.z.t/n defines an IP address in which the leftmost n bits specify the Netid. See ipconfig /all Subnet mask = 255.255.192.0 = 1111 1111-1111 1111-1100 0000- 0000 0000 Netid = logical AND of the IP address and mask HostID = logical AND of the IP address and mask complement
Note that a 16-address block means an address mask of /28. Host addresses differ ONLY in the rightmost 4 bits.
Supernetting Combining smaller physical networks into a single larger one. Could combine several class C networks into a single network.
Example Class C NetworkBit RepresentationAddress Range 211.195.8.011010011-11000011-00001000-xxxxxxxx188.8.131.52 to 184.108.40.206 211.195.9.011010011-11000011-00001001-xxxxxxxx220.127.116.11 to 18.104.22.168 211.195.10.011010011-11000011-00001010-xxxxxxxx22.214.171.124 to 126.96.36.199 211.195.11.011010011-11000011-00001011-xxxxxxxx188.8.131.52 to 184.108.40.206 Address mask is 255.255.252.0 (11111111.11111111.11111100.00000000) All bits the same
Subnetting (reverse of supernetting): Dividing a network into smaller networks All hosts in a single subnet share the same subnet number. Hosts and NetIDs are addressed consecutively Number of addresses in a subnet is a power of 2.
Reasons to subnet Separate different media (e.g. cable from optical fiber) Separate devices that provide different functions such as various types of servers. Security concerns Better reflect the structure of an organization Better manage network traffic
example An organization is given a block of 64 addresses defined by 220.127.116.11/26. This means it has 2 6 =64 IP addresses. It wants 3 subnets of size 16, 16, and 32. Subnet mask for the larger subnet has twenty seven 1s followed by five 0s. The smaller ones have a mask with twenty eight 1’s followed by four 0s A possible arrangement is
19.17 Figure 19.7 Configuration and addresses in a subnetted network
Last 8 bits of the IP addresses, Net IDs underlined 0000-0000 thru 0011-1111 (64 addresses) Subnet 1: 0000-0000 thru 0001-1111 (32 addresses) Subnet 2: 0010-0000 thru 0010-1111 (16 addresses) Subnet 3: 0011-0000 thru 0011-1111 (16 addresses)
NAT (Network address translation) based router: If you all buy the same router from Best Buy, chances are your computers will ALL have the same IP address given to it by the router. For example: 192.168.x.x is a private address space.private address space internet LAN NAT-based router 192.168.0.2 192.168.0.4 192.168.0.3 A C B 18.104.22.168 Assigned by ISP Addresses assigned by router
Book covers a couple of designs; we’ll cover just their last one Router has IP address Each device behind the router has an IP address, BUT router hides them from the Internet world. A packet sent from a device to the router contains a source IP address (w) and port # (x) Router replaces them both with a fixed IP address (y) and another port # (z) and forwards packet to the internet. Returning responses will be sent to y
Router maintains a table that relates (w, x) and (y, z) Packet from Internet arrives at router; router looks up address in the NAT table It substitutes and forwards the packet.
Advantages: Hides IP addresses from Internet world allows IP addresses to be reused eliminates some tasks associated with managing subnets (NAT-based router does it) useful for home networks where consumer does not want to manage IP addresses NAT-based router looks like a single device to the Internet world
Disadvantages: Purists object to using port numbers to identify addresses (when they were designed to identify applications). Some see it as a kludge (pronounced klooj – nonstandard technique) to solve a problem that should be solved via IPv6 other other
IPv6 – section 19.2 but just the highlights There are not enough IPv4 addresses IPv6 uses a 128-bit address
19.26 Figure 19.14 IPv6 address in binary and hexadecimal colon notation
Can specify Registry: which agency registered the address (INTERNIC for north America, RIPNIC for Europe, APNIC for Asia and Pacific countries)INTERNIC APNIC Provider: e.g. your ISP Subscriber: e.g. a provider’s customer Subnet: if the subscriber is an organization, it may have multiple subnets. Node: the device.
IPv6 also provides Security Streaming support Streamlined packets and more flexible packet headers for quicker routing Authentication It has been in the process of being phased in for years.
Section 20.1 Internetworking Not a lot here, mostly setting the context and we’ve seen this before.
20.31 Figure 20.2 Network layer in an internetwork
IP Packet (also a datagram) contents See the book for most details but a couple of relevant things follow. Source & destination addresses. Time-To-Live (TTL) field – decremented by one each time a router forwards the packet. When it is 0, it is discarded.
Checksum (on header only) – for error detection. Needs to be recalculated at each router since the header can change. Checksumming the header only is quicker Higher level protocols will error check the data if needed.
Fragmentation bits. The IP protocol allows for the possibility that an IP packet might travel a network that forces an IP packet to divided into smaller pieces. You can skip this section. Priority bits – could allow a router to prioritize the packets it has in case of congestion. It was never really used. Type of service (TOS) bits allow an app to request a type of handling.
That same field also allows differentiated services – the ability of a router to examine this field and to determine the quality of service (QoS) expected of the higher layer. E.g. a file transfer or streaming real-time data. Bits to define the protocol above IP using its services. Allows the specification of a route to follow or to record the route taken.
Sections 20.3 and 20.4 deal with IPv6 and the transition from IPv4 to IPv6. It’s not difficult reading but I won’t cover it. Be aware of the issues however.
Section 21.1 Address mapping Will cover ARP (address resolution protocol) only – and only a general description of it.
The problem Sender sends an IP packet across the Internet to a remote device. Intermediate routers will route based solely on destination IP address. The last router must deliver the IP packet directly to the device, most likely by embedding the IP packet into an Ethernet frame and sending it over the underlying LAN. How does it determine the physical address?
ARP (Address Resolution Protocol). Router sends a broadcast (containing the IP address) to all devices on a LAN. Device associated with that IP address responds by sending its MAC address. Router stores that info and then embeds the IP packet in a MAC frame and sends it. The following diagram illustrates but I will not go into detail with regard to the ARP packet format or variations of this. It’s accessible to you based on what we’ve covered.
Network Layer: Routing and IP Problem A network may be visualized as a graph Find a route from S (source address) to D (destination address) Does it matter which you choose?
An edge may have costs Cost of a route = sum of edge costs May just treat all edges the same (cost=1) Cost of route = number of edges (number of hops)
Delivery: Section 22.1 Direct delivery Packet goes from one device to a destination located on the same physical network Indirect delivery Packet goes through multiple devices on its way to its destination. Devices are routers. Last router is on the same physical network as the destination. From there, it’s direct delivery.
Forwarding: Section 22.2 A router will: receive a packet and send it to some other router or to the destination. Route method: Either the router or packet contains the complete route Can be used by some maintenance protocols to test routes, but not common. Next Hop method Router knows ONLY the next router (hop) in a path Analogies to the US mail
In this case, the next node is along a “cheapest path”. If all costs are 1, then cheapest is shortest. Other criteria might be used
Method of forwarding Host specific Router has one table entry for every possible destination Not realistic Network specific Router has one table entry for each physical network that is reachable. It identifies the network number. One entry for all destinations on the same physical network.
22.52 Figure 22.3 Host-specific versus network-specific method
Router actions Get packet and extract IP address If source route is specified, extract info and route, otherwise Determine Netid from the IP packet and search the routing table If Netid found and router attached to that network determine physical address via ARP. Embed packet into an Ethernet frame and send. Otherwise
If Netid found and router not attached to that network send over link specified in the routing table If Netid is not found send to default router.
22.55 Figure 22.6 Configuration for Example 22.1
22.56 Table 22.1 Routing table for router R1 in Figure 22.6
Skip the rest of 22.3 after the previous example
Routing protocols Autonomous system (AS): collection of networks and routers under a single administration. Autonomous system single administration Intradomain routing: routing inside an AS Interdomain routing: routing between AS’s
Routing Information Protocol (RIP) An implementation of a distance vector protocol. Route with minimum distance Minimum is shortest if all edge costs are 1. In that case the cost is the hop count.
Bellman-Ford (also Distance vector). Based on the principle of optimality
Distance vector algorithm Routing table contains possible destinations, costs to get there, and the next node in the route. Get information from each neighbor’s routing table. Is it cheaper to get to a node by going through that neighbor first? If so, update the entry in the current routing table.
Each row is a routing table for the node at the left end
Linux traceroute command DOS tracert command on australia.net, hawaii.net, alaska.net See [http://www.uwgb.edu/serverstatus/netmanagement/ wiscnet.htm]http://www.uwgb.edu/serverstatus/netmanagement/ wiscnet.htm
Distance Vector Routing has some problems when routers are connected in a loop but there are ways to deal with them. That would be for a second class.
Link State Routing Each router shares its routing table with all others. Over time, each router learns the network topology Can apply algorithms such as Dijkstra’s algorithm to find the cheapest path to any destination. Neither Link State nor distance vector routing scale well to LARGE numbers of routers. Again – they are intradomain routing
Border Gateway Protocol Based on a path vector routing algorithm Interdomain routing Routes among speaker nodes (one that acts for an entire AS); there is one for each AS Speaker nodes communicate, indicating accessibility to nodes within their domain.