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Comparison of Connectionless Network Layer Protocols

Comparison of Connectionless Network Layer Protocols 25
Comparison of Connectionless Network Layer Protocols Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 1Forwarding Models  Connectionoriented:  ATM, X.25, framerelay…  Connectionless:  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, Providerbased 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 routerless 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 mid90s 32 bits (4bytes) Network Host Flexible boundary: decided by mask. CIDR/supernetmask used by provider for netID Subnet mask for intraAS 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 routerless LAN: need a DHCP server at least. Same prefix = same LAN; ARP  Bottomline: server necessary for IP autoconfiguration on LAN. Serverless 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  Plugnplay: 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, nonunique 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  Intradomain 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+ Autoconfiguration  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 routerless LAN: Same prefix = same LAN; nodeID = LAN addr; default prefix = 0 also works  IPX has the simplest serverless autoconfiguration 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  NSelector (NSEL): like UDP ports  Variable length with 20byte 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 IPCIDR.  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 nodeaddress  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 (08 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 ESIS protocol  Can do cool things like embedding X.25 DTE addresses in area part, and inferring phonenumbers from CLNP addreses Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 12CLNP Autoconfiguration: ESIS Protocol  1,4. Endnode acquire L3 address, and find default router by listening/querying for an hello from routers (ISHello).  Address = area prefix from router + IEEE address  2,3. Router finds endnode’s L3 L2 address by having endnodes advertise a EShello as part of ESIS.  Unlike IP it cannot look at areaID and assume direct connectivity  5,6. Endnodes 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 ARPlike 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 Autoconfiguration  1. Endnode acquires L3 address:  Discover router and netID range by snooping for RIPlike 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 endnode: same netID  3. Router finds L2 address of endnode: ARP  4. Endnodes find router: solicit/listen for router traffic  5. Endnodes send directly to each other: in range = direct  6. Best router discovery: snoop on received traffic  7. Routerless 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 autoconfiguration, and done with short address space Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 15DECnet Phase IV  Was meant as a transition protocol, but CLNP delayed  2byte addresses: 6bits area, 10bits node  Shortest L3 address among all L3 protocols seen…  Bold autoconfiguration hack:  Directly compute 6byte IEEE address from 2byte DECnet address  DEC OUI + 0byte = AA000400 (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  IntraLAN bit in header to inform receivers of direct connectivity  Else one hop through router even for direct case Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 16DECnet autoconfiguration  1. End nodes get L3 address: manually configured (ugh)  2. Router finds L3 address of endnode: EShellos like in CLNP  3. Router finds L2 address of endnode: HIORD+L3 address Bold  4. Endnodes find a router: router (IS) hellos like CLNP  5. Endnodes send directly: intraLAN bit in rcvd packets  6. Bestexit router: Learn from rcvd traffic like Appletalk  7. Routerless LAN: No problem HIORD + L3 address  Bold solution, with smallest address size.  Penalty: endnodes 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 hostID IPX,CLNP,IPv6 (EUI)  LAN addr = HIORD + L3 addr DECnet  ESHellos and ISHellos CLNP, DECnet  Snoop on RIP traffic for router info Appletalk, IPX  Bestexit inferred from rcvd traffic DECnet, Appletalk  Redirects for bestrouter only (IP, IPv6, IPX)  Redirects for bestrouter and direct endnode (CLNP)  IntraLAN flag for direct endnode (DECnet) Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 19Packet Formats IP IPv6 Similarity: Same core methods Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 20Packet Formats DECnet, Phase IV CLNP Similarity: Address refers to node Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 21Packet Formats (Contd) Appletalk Similarity: Address = interface Cool autoconfiguration IPX, IPX+ Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 22Header Design Issues  Nonadjacent address components (IPX, IPX+, Appletalk)  TTL:  time (CLNP) vs hop count (IP, IPv6)  Counts up (IPX,vs counts down (IP, CLNP)  UDPlike port space in L3 header vs L4 header  Small diffs in fragmentation/reassembly (IP, IPv6, CLNP)  Don’t care about fragmentation/reassembly (Appletalk, DECnet)  ICMP functions requested (CLNP, DECnet)  ICMP separate protocol (IP, IPv6)  No error reporting (IPX, Appletalk)  Fixed vs Variable length header/fields  Header checksum (CLNP different algorithm) Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 23Summary  Addressing and autoconfiguration are primary differences in connectionless protocols  Minor differences in other aspects of header design and forwardingplane operation Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 24
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