Which protocol provides connectionless network layer services

Comparison of Connectionless Network Layer Protocols and protocol provides connectionless network layer services
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Published Date:19-07-2017
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Comparison of Connectionless Network Layer Protocols Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 1Forwarding Models  Connection-oriented:  ATM, X.25, frame-relay…  Connection-less:  IP, IPv6  CLNP  IPX, IPX+  Decnet  Appletalk  Major differences in addressing and related issues: allocation, configuration, resolution, hierarchy…  Minor differences in formats/encoding, TTL/hop count, fragmentation etc Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 2Addressing Differences  Node or interface:  IP, IPX, IPv6, Appletalk address interfaces  CLNP, Decnet: addresses for nodes. Nodes w/ multiple interfaces in same area can have single address  Hierarchy: fixed or variable boundaries  Locator (network ID) + Host ID  IP, IPX, CLNP: arbitrary number of levels  Classful IP: fixed boundaries  Owning vs Renting addresses:  Original IP model: own address  DHCP, Provider-based addressing, IPv6 address lifetime: rent addresses  Rent = renumbering overhead. NAT helps  Configuration ease: facilitates stateless, easy address resolution/neighbor discovery? Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 3Recall: 7 Things to (auto-) configure…  1. End systems need Layer 3 address, names, masks  2. Router finds Layer 3 addresses of end systems  3. Router finds Layer 2 addresses of end systems  4. End systems find a (default) router, name server  5. End nodes on the same LAN discover that they can send directly to each other  6. End systems find the best router for exit traffic  7. End systems communicate on a router-less LAN  Typically end systems only know their hardware (IEEE 802) address… Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 4Address structures: IP  4 bytes, subnet/CIDR mask for flexible boundaries, arbitrary levels. Original: classful; Current: classless  ARP for address resolution. Small IP address = cannot derive Ethernet address from IP address  BOOTP/DHCP (stateful configuration). No stateless auto- configuration features  Addresses centrally assigned; then moved to provider- based + private/NAT model in mid-90s 32 bits (4bytes) Network Host Flexible boundary: decided by mask. CIDR/supernet-mask used by provider for netID Subnet mask for intra-AS assignment Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 5IP Configuration  1. End systems: Layer 3 address, names, masks: DHCP  2. Router finds Layer 3 addresses of end systems: Same network ID (I.e. IP prefix)  3. Router finds Layer 2 addresses of end systems: ARP  4. End systems find a default router, name server: DHCP  5. End nodes on the same LAN discover that they can send directly to each other: Same network ID + ARP  6. End systems find the best router for exit traffic: ICMP Router Redirect  7. End systems communicate on a router-less LAN: need a DHCP server at least. Same prefix = same LAN; ARP  Bottom-line: server necessary for IP auto-configuration on LAN. Server-less not possible. Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 6Address Structure: IPX, IPX+  Internetworking Packet Exchange (IPX)  IPX: 10 bytes. IPX+: 16 bytes = larger than IP  Simple structure:  IPX: 4B NetID + 6B Node ID.  IPX+: Adds 6B Domain ID  6 byte NodeID = IEEE link address = no ARP needed Address resolution w/o traffic overhead or delays  Plug-n-play: Node boots with LAN address, broadcasts to ask for net ID 6bytes 4bytes Network Host Fixed boundary Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 7IPX  No registry = many little IPX nets, non-unique assignments  Internal network number: servers deplete netIDs to get better routes. Adds configuration overhead. Lousy feature. net 57 net 57 x x “net” 91 R S S = R y y net 29 net 29 C C Internal network number example for IPX Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 8IPX+  IPX+: Adds “domain number” in an expanded header  Intra-domain routers need not be upgraded  NetID FFFC reserved to reach domain boundary  Boundary routers then uses expanded header Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 9IPX, IPX+ Auto-configuration  1. End systems acquire link prefix: snoop/solicit for router advts. L3 address = prefix + IEEE address  2. Router finds L3 addr of end systems: Same network ID  3. Router finds L2 addr of end systems: nodeID in addr  4. End systems find a default router: solicit for advt  5. End nodes on the same LAN send directly to each other: Same network ID= direct; nodeID gives LAN addr  6. End systems find the best router for exit traffic: End node asks for best router before transmission. (weak)  7. End systems communicate on a router-less LAN: Same prefix = same LAN; nodeID = LAN addr; default prefix = 0 also works  IPX has the simplest server-less auto-configuration solution. Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 10CLNS Addressing: NSAP Format Area ID ID NSEL Variable length Area address AFI System ID NSEL 1 byte 1 - 12 bytes 6 bytes 1 byte  NSAP format has 3 main components  Area ID: globally defined locator  System ID: maps to IEEE 802 LAN address usually  N-Selector (NSEL): like UDP ports  Variable length with 20-byte maximum  Pkt format needs an address length field Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 11Address Structure: CLNP…  Between areas, Level 2 routing operates. Many levels of hierarchy possible, just like IP-CIDR.  Longest prefix match like IP  Area larger than single link, all nodes in the area share the same area prefix.  Within an area, cannot tell which link (subnet) a node is on, because address is a node-address  Advantage: a node can move within area and retain address  I.e., no hierarchy in ID field = flat, no topological significance  Originally ID: 6 bytes, maps to IEEE address like IPX. But ISO allows this to be variable length too (0-8 bytes)  Level 1 routing operates here based upon exact match  Bridging in IP provides similar function to level 1 routing  Unlike IP cannot use netID or prefix match to decide if destination directly connected = need ES-IS protocol  Can do cool things like embedding X.25 DTE addresses in area part, and inferring phone-numbers from CLNP addreses Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 12CLNP Auto-configuration: ES-IS Protocol  1,4. End-node acquire L3 address, and find default router by listening/querying for an hello from routers (IS-Hello).  Address = area prefix from router + IEEE address  2,3. Router finds end-node’s L3 & L2 address by having end-nodes advertise a ES-hello as part of ES-IS.  Unlike IP it cannot look at area-ID and assume direct connectivity  5,6. End-nodes cannot figure out if they are directly connected.  So routers send a redirect after forwarding first packet.  Redirects are also used to get best exit router.  Router, Destination, Neighbor caches like IPv6  7. Routerless LAN: if no router, data packet (not a special ARP-like message) is multicast.  Destination replies with LAN address. Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 13Address structure: Appletalk  Address: 3 bytes long: 2 bytes net ID, 1 byte host  LAN can have a range of net IDs  Similar to subnet mask, but more flexible. Ranges can start and end on any number, not a power of 2  Direct connectivity: Don’t do AND operation with mask = check if address in range  Hosts snoop on received packets to learn best exit router for destinations: no redirects.  Appletalk does no fragmentation/reassembly 2 bytes 1 Byte Network Host Fixed boundary Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 14Appletalk Auto-configuration  1. End-node acquires L3 address:  Discover router and netID range by snooping for RIP-like messages or by broadcasting a query for one.  Host ID: Randomly choose an address in range (cool)  Send message to address hoping not to get a reply  2. Router finds L3 address of end-node: same net-ID  3. Router finds L2 address of end-node: ARP  4. End-nodes find router: solicit/listen for router traffic  5. End-nodes send directly to each other: in range = direct  6. Best router discovery: snoop on received traffic  7. Router-less LAN: same range = direct. Else default range.  Miscl: Zone concept to limit name resolution broadcasts  Routers on LAN learn range from seed router in LAN  Cutest solution to auto-configuration, and done with short address space Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 15DECnet Phase IV  Was meant as a transition protocol, but CLNP delayed  2-byte addresses: 6-bits area, 10-bits node  Shortest L3 address among all L3 protocols seen…  Bold auto-configuration hack:  Directly compute 6-byte IEEE address from 2-byte DECnet address  DEC OUI + 0-byte = AA-00-04-00 (aka HIORD)  Program ethernet chips to ignore hardware address and listen to HIORD+DECnet address instead  Like CLNP, address refers to node (not I/f) within area  Intra-LAN bit in header to inform receivers of direct connectivity  Else one hop through router even for direct case Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 16DECnet auto-configuration  1. End nodes get L3 address: manually configured (ugh)  2. Router finds L3 address of end-node: ES-hellos like in CLNP  3. Router finds L2 address of end-node: HIORD+L3 address Bold  4. End-nodes find a router: router (IS) hellos like CLNP  5. End-nodes send directly: intra-LAN bit in rcvd packets  6. Best-exit router: Learn from rcvd traffic like Appletalk  7. Router-less LAN: No problem HIORD + L3 address  Bold solution, with smallest address size.  Penalty: end-nodes need manual configuration. Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 17Comparison of Address Formats 4 bytes Boundary depends on IP mask IPX 4 6 2 bytes total DECnet Ph IV 6 bits area Appletalk 10 bits node 2 1 up to 14 6 CLNP IPv6 8 8 Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 18(Auto-) configuration Techniques  Manually configure hosts and routers DECnet  Manually configure routers only IP, IPv6, IPX, Appletalk (seed router), CLNP  DHCP server IP, IPv6 (optional)  ARP IP, Appletalk  IEEE address embedded in host-ID IPX,CLNP,IPv6 (EUI)  LAN addr = HIORD + L3 addr DECnet  ES-Hellos and IS-Hellos CLNP, DECnet  Snoop on RIP traffic for router info Appletalk, IPX  Best-exit inferred from rcvd traffic DECnet, Appletalk  Redirects for best-router only (IP, IPv6, IPX)  Redirects for best-router and direct end-node (CLNP)  Intra-LAN flag for direct end-node (DECnet) Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 19Packet Formats IP IPv6 Similarity: Same core methods Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 20