Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 1 Comparison of Connectionless Network Layer Protocols Or Shivkumar Kalyanaraman Rensselaer Polytechnic Institute Based in part upon slides of I. Stoica (UCB)

Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 2 Forwarding Models q Connection-oriented: q ATM, X.25, frame-relay… q Connection-less: q IP, IPv6 q CLNP q IPX, IPX+ q Decnet q Appletalk q Major differences in addressing and related issues: allocation, configuration, resolution, hierarchy… q Minor differences in formats/encoding, TTL/hop count, fragmentation etc

Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 3 Addressing Differences q Node or interface: q IP, IPX, IPv6, Appletalk address interfaces q CLNP, Decnet: addresses for nodes. Nodes w/ multiple interfaces in same area can have single address q Hierarchy: fixed or variable boundaries q Locator (network ID) + Host ID q IP, IPX, CLNP: arbitrary number of levels q Classful IP: fixed boundaries q Owning vs Renting addresses: q Original IP model: own address q DHCP, Provider-based addressing, IPv6 address lifetime: rent addresses q Rent => renumbering overhead. NAT helps q Configuration ease: facilitates stateless, easy address resolution/neighbor discovery?

Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 4 Recall: 7 Things to (auto-) configure… q 1. End systems need Layer 3 address, names, masks q 2. Router finds Layer 3 addresses of end systems q 3. Router finds Layer 2 addresses of end systems q 4. End systems find a (default) router, name server q 5. End nodes on the same LAN discover that they can send directly to each other q 6. End systems find the best router for exit traffic q 7. End systems communicate on a router-less LAN q Typically end systems only know their hardware (IEEE 802) address…

Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 5 Address structures: IP q 4 bytes, subnet/CIDR mask for flexible boundaries, arbitrary levels. Original: classful; Current: classless q ARP for address resolution. Small IP address => cannot derive Ethernet address from IP address q BOOTP/DHCP (stateful configuration). No stateless auto- configuration features q Addresses centrally assigned; then moved to provider- based + private/NAT model in mid-90s NetworkHost Flexible boundary: decided by mask. CIDR/supernet-mask used by provider for netID Subnet mask for intra-AS assignment 32 bits (4bytes)

Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 6 IP Configuration q 1. End systems: Layer 3 address, names, masks: DHCP q 2. Router finds Layer 3 addresses of end systems: Same network ID (I.e. IP prefix) q 3. Router finds Layer 2 addresses of end systems: ARP q 4. End systems find a default router, name server: DHCP q 5. End nodes on the same LAN discover that they can send directly to each other: Same network ID + ARP q 6. End systems find the best router for exit traffic: ICMP Router Redirect q 7. End systems communicate on a router-less LAN: need a DHCP server at least. Same prefix => same LAN; ARP q Bottom-line: server necessary for IP auto-configuration on LAN. Server-less not possible.

Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 7 Address Structure: IPX, IPX+ q Internetworking Packet Exchange (IPX) q IPX: 10 bytes. IPX+: 16 bytes => larger than IP q Simple structure: q IPX: 4B NetID + 6B Node ID. q IPX+: Adds 6B Domain ID q 6 byte NodeID = IEEE link address => no ARP needed! Address resolution w/o traffic overhead or delays q Plug-n-play: Node boots with LAN address, broadcasts to ask for net ID NetworkHost 4bytes 6bytes Fixed boundary!

Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 8 IPX q No registry => many little IPX nets, non-unique assignments q Internal network number: servers deplete netIDs to get better routes. Adds configuration overhead. Lousy feature. => R S C x y net #57 net #29 “net” 91 Internal network number example for IPX

Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 9 IPX+ q IPX+: Adds “domain number” in an expanded header q Intra-domain routers need not be upgraded q NetID FFFC reserved to reach domain boundary q Boundary routers then uses expanded header

Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 10 IPX, IPX+ Auto-configuration q 1. End systems acquire link prefix: snoop/solicit for router advts. L3 address = prefix + IEEE address q 2. Router finds L3 addr of end systems: Same network ID q 3. Router finds L2 addr of end systems: nodeID in addr! q 4. End systems find a default router: solicit for advt q 5. End nodes on the same LAN send directly to each other: Same network ID=> direct; nodeID gives LAN addr q 6. End systems find the best router for exit traffic: End node asks for best router before transmission. (weak!) q 7. End systems communicate on a router-less LAN: Same prefix => same LAN; nodeID = LAN addr; default prefix = 0 also works q IPX has the simplest server-less auto-configuration solution.

Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 11 CLNS Addressing: NSAP Format System IDNSELAFI Variable length Area address 6 bytes1 byte bytes q NSAP format has 3 main components q Area ID: globally defined locator q System ID: maps to IEEE 802 LAN address usually q N-Selector (NSEL): like UDP ports q Variable length with 20-byte maximum q Pkt format needs an address length field! Area IDID NSEL

Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 12 Address Structure: CLNP… q Between areas, Level 2 routing operates. Many levels of hierarchy possible, just like IP-CIDR. q Longest prefix match like IP q Area larger than single link, all nodes in the area share the same area prefix. q Within an area, cannot tell which link (subnet) a node is on, because address is a node-address q Advantage: a node can move within area and retain address q I.e., no hierarchy in ID field => flat, no topological significance q Originally ID: 6 bytes, maps to IEEE address like IPX. But ISO allows this to be variable length too (0-8 bytes) q Level 1 routing operates here based upon exact match q Bridging in IP provides similar function to level 1 routing q Unlike IP cannot use netID or prefix match to decide if destination directly connected => need ES-IS protocol q 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 13 CLNP Auto-configuration: ES-IS Protocol q 1,4. End-node acquire L3 address, and find default router by listening/querying for an hello from routers (IS-Hello). q Address = area prefix from router + IEEE address q 2,3. Router finds end-node’s L3 & L2 address by having end-nodes advertise a ES-hello as part of ES-IS. q Unlike IP it cannot look at area-ID and assume direct connectivity q 5,6. End-nodes cannot figure out if they are directly connected. q So routers send a redirect after forwarding first packet. q Redirects are also used to get best exit router. q Router, Destination, Neighbor caches like IPv6 q 7. Routerless LAN: if no router, data packet (not a special ARP-like message) is multicast. q Destination replies with LAN address.

Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 14 Address structure: Appletalk q Address: 3 bytes long: 2 bytes net ID, 1 byte host q LAN can have a range of net IDs q Similar to subnet mask, but more flexible. Ranges can start and end on any number, not a power of 2 q Direct connectivity: Don’t do AND operation with mask => check if address in range q Hosts snoop on received packets to learn best exit router for destinations: no redirects. q Appletalk does no fragmentation/reassembly Network Host 2 bytes 1 Byte Fixed boundary!

Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 15 Appletalk Auto-configuration q 1. End-node acquires L3 address: q Discover router and netID range by snooping for RIP-like messages or by broadcasting a query for one. q Host ID: Randomly choose an address in range! (cool!) q Send message to address hoping not to get a reply! q 2. Router finds L3 address of end-node: same net-ID q 3. Router finds L2 address of end-node: ARP q 4. End-nodes find router: solicit/listen for router traffic q 5. End-nodes send directly to each other: in range => direct q 6. Best router discovery: snoop on received traffic q 7. Router-less LAN: same range => direct. Else default range. q Miscl: Zone concept to limit name resolution broadcasts q Routers on LAN learn range from seed router in LAN q Cutest solution to auto-configuration, and done with short address space!

Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 16 DECnet Phase IV q Was meant as a transition protocol, but CLNP delayed q 2-byte addresses: 6-bits area, 10-bits node q Shortest L3 address among all L3 protocols seen… q Bold auto-configuration hack: q Directly compute 6-byte IEEE address from 2-byte DECnet address!! q DEC OUI + 0-byte = AA (aka HIORD) q Program ethernet chips to ignore hardware address and listen to HIORD+DECnet address instead!! q Like CLNP, address refers to node (not I/f) within area q Intra-LAN bit in header to inform receivers of direct connectivity q Else one hop through router even for direct case

Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 17 DECnet auto-configuration q 1. End nodes get L3 address: manually configured (ugh!) q 2. Router finds L3 address of end-node: ES-hellos like in CLNP q 3. Router finds L2 address of end-node: HIORD+L3 address! Bold! q 4. End-nodes find a router: router (IS) hellos like CLNP q 5. End-nodes send directly: intra-LAN bit in rcvd packets q 6. Best-exit router: Learn from rcvd traffic like Appletalk q 7. Router-less LAN: No problem! HIORD + L3 address! q Bold solution, with smallest address size. q Penalty: end-nodes need manual configuration.

Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 18 Comparison of Address Formats Boundary depends on mask IP 2 bytes total 6 bits area 10 bits node IPX DECnet Ph IV Appletalk CLNP IPv6

Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 19 (Auto-) configuration Techniques q Manually configure hosts and routers {DECnet} q Manually configure routers only {IP, IPv6, IPX, Appletalk (seed router), CLNP} q DHCP server {IP, IPv6 (optional)} q ARP {IP, Appletalk} q IEEE address embedded in host-ID {IPX,CLNP,IPv6 (EUI)} q LAN addr = HIORD + L3 addr {DECnet} q ES-Hellos and IS-Hellos {CLNP, DECnet} q Snoop on RIP traffic for router info {Appletalk, IPX} q Best-exit inferred from rcvd traffic {DECnet, Appletalk} q Redirects for best-router only (IP, IPv6, IPX) q Redirects for best-router and direct end-node (CLNP) q Intra-LAN flag for direct end-node (DECnet)

Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 20 Packet Formats IPIPv6 Similarity: Same core methods

Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 21 Packet Formats CLNP DECnet, Phase IV Similarity: Address refers to node

Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 22 Packet Formats (Contd) IPX, IPX+ Appletalk Similarity: Address = interface Cool auto-configuration

Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 23 Header Design Issues q Non-adjacent address components (IPX, IPX+, Appletalk) q TTL: q time (CLNP) vs hop count (IP, IPv6) q Counts up (IPX,vs counts down (IP, CLNP) q UDP-like port space in L3 header vs L4 header q Small diffs in fragmentation/reassembly (IP, IPv6, CLNP) q Don’t care about fragmentation/reassembly (Appletalk, DECnet) q ICMP functions requested (CLNP, DECnet) q ICMP separate protocol (IP, IPv6) q No error reporting (IPX, Appletalk) q Fixed vs Variable length header/fields q Header checksum (CLNP different algorithm)

Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 24 Summary q Addressing and auto-configuration are primary differences in connectionless protocols q Minor differences in other aspects of header design and forwarding-plane operation