How does internetworking work

what is internetworking in computer network and what is internetworking devices.what is difference between internetworking and networking pdf free download
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Published Date:23-07-2017
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' COMPUTER NETWORKS CS 45201 CS 55201 CHAPTER 4 Internetworking H. Peyravi and P. Farrell Department of Computer Science Kent State University Kent, Ohio 44242 farrellcs.kent.edu http://www.cs.kent.edu/farrell Fall 2001 & % CS 4/55201: Computer Networks Fall 2001' Contents  Internetworking  Global Internet  Route Propagation  Next Generation IP (IPv6)  Internet Multicasting  Host Names (DNS) & % CS 4/55201: Computer Networks Fall 2001Chapter 4: Internetworking Internetworking ' Internetworking De nition: Logical network built from multiple physical networks. Network 1 (Ethernet) Hn = Host Rn = Router H7 R3 H8 H1 H2 H3 Network 4 (point-to-point) Network 2 (Ethernet) R1 R2 H4 Network 3 (Token Ring) H5 H6 H1 H8 TCP TCP R1 R2 R3 IP IP IP IP IP ETH ETH FDDI FDDI P2P P2P ETH ETH & % CS 4/55201: Computer Networks Fall 2001 1 of 48Chapter 4: Internetworking Internetworking ' IP Service Model  Packet Delivery Model  Global Addressing Scheme IP Datagram Packet Delivery Model  Connection-less (datagram-based)  Best-e ort delivery (unreliable service) I packets are lost I packets are delivered out of order I duplicate copies of a packet are delivered I packets can be delayed for a long time  TCP/IP standards given by RFCs (Request-for-Comments) & % CS 4/55201: Computer Networks Fall 2001 2 of 48Chapter 4: Internetworking Internetworking ' 0 4 8 16 19 31 Version HLen TOS Length Ident Flags Offset TTL Protocol Checksum SourceAddr DestinationAddr Pad Options (variable) (variable) Data  Datagram format I Version (4): currently 4 I Hlen (4): number of 32-bit words in header I TOS (8): type of service (not widely used) I Length (16): number of bytes in this datagram I Ident (16): used by fragmentation I Flags/O set (16): used by fragmentation I TTL (8): number of hops this datagram has traveled I Protocol (8): demux key (TCP=6, UDP=17) I Checksum (16): of the header only I DestAddr & SrcAddr (32) & % CS 4/55201: Computer Networks Fall 2001 3 of 48Chapter 4: Internetworking Internetworking ' Fragmentation and Reassembly  Each network has some MTU (Max Transmission Unit)  Strategy I fragment when necessary (MTU Datagram) I IP packet needs to t in payload part of frame I use CS-PDU (not cells) for ATM =) CS: convergence sublayer I try to avoid fragmentation at source host I refragmentation is possible at routers etc. I fragments are self-contained datagrams I all fragments contain same value in ident eld I each fragment is re-encapsulated in frame I delay reassembly until destination host I do not recover from lost fragments  Example & % CS 4/55201: Computer Networks Fall 2001 4 of 48Chapter 4: Internetworking Internetworking ' H1 H8 R2 R3 R1 (1400) (1400) (512) ETH IP FDDI IP P2P IP (512) ETH IP (512) P2P (512) ETH IP IP (376) (376) P2P ETH IP IP & % CS 4/55201: Computer Networks Fall 2001 5 of 48Chapter 4: Internetworking Internetworking ' Start of header ident = x 0 offset = 0 Rest of header 1400 data bytes Unfragmented Packet Start of header ident = x 1 offset = 0 Rest of header 512 data bytes First Fragment Start of header ident = x 1 offset = 512 Rest of header 512 data bytes Second Fragment Start of header ident = x 0 offset = 1024 Rest of header 376 data bytes Last Fragment & % CS 4/55201: Computer Networks Fall 2001 6 of 48Chapter 4: Internetworking Internetworking ' Global Addresses  Properties I globally unique I hierarchical: network + host  Format 7 24 Class A 0 network host 14 16 Class B 1 0 network host 21 8 Class C 1 1 0 network host  Dot notation I 10.3.2.4 I 128.96.33.81 I 192.12.69.77 & % CS 4/55201: Computer Networks Fall 2001 7 of 48Chapter 4: Internetworking Internetworking ' Datagram Forwarding  Strategy I every datagram contains destination's address I if directly connected to destination network, then forward to host I if not directly connected to destination network, then forward to some router I forwarding table maps network number into next hop I each host has a default router I each router maintains a forwarding table H1 H8 TCP TCP R1 R2 R3 IP IP IP IP IP ETH ETH FDDI FDDI P2P P2P ETH ETH  Example (router R2) Network Number Next Hop 1 R3 2 R1 3 interface 1 4 interface 0 & % CS 4/55201: Computer Networks Fall 2001 8 of 48Chapter 4: Internetworking Internetworking ' Address Translation  Map IP addresses into physical addresses I destination host I next hop router  Techniques I encode physical address in host part of IP address I table-based  ARP (Address Resolution Protocol) I table (cache) of IP to physical address bindings I broadcast request if IP address not in table I target machine responds with its physical address I table entries are discarded if not refreshed  Notes I table entries timeout in about 10 minutes I update table with source when you are the target I refresh table if already have an entry I do not refresh table entries upon reference I do not add to table if not there and not target & % CS 4/55201: Computer Networks Fall 2001 9 of 48Chapter 4: Internetworking Internetworking '  Request format HardwareType=1 ProtocolType=0x0800 HLEN=48 PLEN=32 Operation SourceHardwareAddr SourceProtocolAddr SourceHardwareAddr SourceProtocolAddr TargetHardwareAddr TargetHardwareAddr TargetProtocolAddr I HardwareType: type of physical network (e.g., Ethernet) I ProtocolType: type of higher layer protocol (e.g., IP) I HLEN & PLEN: length of physical and protocol addresses I Operation: request or response I Source/Target Physical/Protocol addresses & % CS 4/55201: Computer Networks Fall 2001 10 of 48Chapter 4: Internetworking Internetworking ' The Address Resolution Protocol, ARP  Every machine on the Internet has one (or more) IP addresses.  These addresses cannot be used for sending packets because data link layer does not understand IP addresses.  LAN addresses are 48-bit and they know nothing about 32-bit IP addresses.  How do IP addresses get mapped onto the data link layer address. I The upper layer software builds a packet with 192.31.65.5 as destination address and gives it to IP software to transmit. I The IP software can look at the address to see whether it is local, but it needs the corresponding Ethernet address. I One solution is to have a con guration le to map IP addresses to LAN addresses, but it is not practical for large number of hosts. I Another solution is to broadcast a packet onto the LAN asking who own the address 192.31.65.5? I The destination responds with its LANS address and the source learns the destination LAN address. This is called ARP.  At this point the IP software builds an Ethernet frame addressed to the destination, puts the IP packet in the payload eld and dumps it on to the Ethernet. The destination detects the frame, reorganize it. The Ethernet driver extract the IP packet from the payload and passes it to the IP software. & % CS 4/55201: Computer Networks Fall 2001 11 of 48Chapter 4: Internetworking Internetworking '  One optimization is to cache the address in case it will be needed soon.  Another optimization is to have every machine broadcast its mapping when it boots.  For remote LAN access, ARP fails, there are two solutions: I The local router could be con gured to respond to ARP request to other LANs. This is called proxy ARP. I Have the source send all nonlocal trac to a default LAN when ARP fails locally. & % CS 4/55201: Computer Networks Fall 2001 12 of 48Chapter 4: Internetworking Internetworking ' The Reverse Address Resolution Protocol, RARP  ARP solves the problem of nding an Ethernet address from an IP address.  Sometime the reverse problem has to solved; nding the IP address from the Ethernet address(booting a diskless workstation).  This protocol allows a newly-booted workstation to broadcast its 48-bit Ethernet address and ask: "Does anyone out there know my IP address?"  The RARP server sees this request, looks up the Ethernet address in its con guration le and sends back the corresponding IP address.  A RARP server is needed on each network.  An alternative protocol is called BOOTP (bootstrap) protocol that uses UDP(user data protocol) messages which are forwarded over routers.  It also provide a diskless workstation with additional information, including the IP address of the le server holding the memory image, the IP address of the default router. & % CS 4/55201: Computer Networks Fall 2001 13 of 48Chapter 4: Internetworking Internetworking ' Internet Control Message Protocol  Echo (ping)  Redirect (from router to source host)  Destination unreachable (protocol, port, or host)  TTL exceeded (so datagrams don't cycle forever)  Checksum failed  Reassembly failed  Cannot fragment  The Internet operations is closely monitored by the routers.  All unexpected events are reported by the ICMP (Internet Control Message Protocol), which is used to test the Internet.  About a dozen types of ICMP messages are de ned. The principal ICMP message types Message type Description Destination unreachable Packet could not be delivered Time exceeded Time to live hit 0 Parameter problem Invalid header eld Source quench Choke packets Redirect Teach a router about geography Echo request Ask a machine if it is alive Echo reply Yes, I am alive Timestamp request Same as Echo request, but with timestamp Timestamp reply Same as Echo reply, but with timestamp & % CS 4/55201: Computer Networks Fall 2001 14 of 48Chapter 4: Internetworking Internetworking ' Dynamic Host Con guration Protocol (DHCP)  Allow automatic con guration from DHCP sever of: I IP address (can be static in table indexed by hardware address OR dynamically assigned from pool (periodic renewal required)) I default router  DHCP server identi cation I host broadcasts DHCP DISCOVER message I carried in UDP packet I if DHCP server local replies I otherwise relayed by relay agent & % CS 4/55201: Computer Networks Fall 2001 15 of 48Chapter 4: Internetworking Internetworking ' Virtual Networks & Tunnels  implement VPN using IP  allow only members of VPN to access  tunnel is established between routers  router encapsulates packet in IP datagram with destination address of router at other end of tunnel Internetwork Network 1 R1 R2 Network 2 10.0.0.1 IP header, IP header, IP header, Destination = 2.x Destination = 10.0.0.1 Destination = 2.x IP header, IP payload IP payload Destination = 2.x IP payload Network Number NextHop 1 Interface 0 2 Interface 0 Default Interface 1  Why? I Security I connect routers with enhanced capability (mulitcast MBone) I carry non-Ip packets (IPX) I make machines at both ends seem like on same network & % CS 4/55201: Computer Networks Fall 2001 16 of 48Chapter 4: Internetworking Global Internet ' Global Internet Internet Structure =) Recent Past NSFNET Backbone Stanford ISU BARNET MidNet Regional Regional Westnet Regional Berkeley PARC UNL KU UNM NCAR UA =) Today Service Provided Backbone Stanford ISU BARNET MidNet Regional Regional Westnet Regional Berkeley PARC UNL KU UNM NCAR UA & % CS 4/55201: Computer Networks Fall 2001 17 of 48 . . .Chapter 4: Internetworking Global Internet ' Scalability Issues =) IP \hides" hosts in address hierarchy, but...  Inecient use of address space I class C network with 2 hosts (2/255 = 0.78% ecient) I class B network with 256 hosts (256/65535 = 0.39% ecient)  Too many networks I today's Internet has tens of thousands of networks I routing tables do not scale I route propagation protocols do not scale & % CS 4/55201: Computer Networks Fall 2001 18 of 48

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