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LAN Addressing Network Protocols and Standards Autumn 2004-2005 Dec 14, 2006 CS573: Network Protocols and Standards 1 An Internet Connection End stations are connected to LANs LANs are connected through Bridges to form extended LANs Extended LANs are connected through gateways/routers/switches Layered architecture Connection is between “peers” Service Models (Fig. 1.3 of Perlman) PDUs (between peers) and SDUs(from up layers) Dec 14, 2006 CS573: Network Protocols and Standards 2 Local Area Networks First part of the course IEEE 802 Committee LAN Standardization Physical and Data Link Layers of OSI Model Data Link layer subdivided by them: MAC (Dependent on the type of LAN) LLC (allows sharing data link resources) Several LANs were standardized Dec 14, 2006 CS573: Network Protocols and Standards 3 IEEE 802 Subcommittees 802.1 --- common issues 802.2 --- LLC Does not deal with PHY and MAC Data Link 802.3 --- CSMA/CD 802.4 --- Token Bus 802.5 --- Token Ring Dec 14, 2006 CS573: Network Protocols and Standards Type 1, 2, … LLC MAC PHY 4 LAN Addresses Most LANs are “broadcast” type LAN addresses solve two problems on shared (or broadcast) LANs Who is the sender? Who is the receiver? IEEE 802 standardized the address length Two different lengths were chosen 16 bit (unique on the network) --- obsolete 48 bit (unique globally --- plug and play) Dec 14, 2006 CS573: Network Protocols and Standards 5 48 bit LAN Addresses Globally unique Assigned by IEEE Cost is $1250 for a “block” of addresses A “block” includes 224 addresses 1st octet 2nd octet 3rd octet Vendor code (OUI) Dec 14, 2006 4th octet 5th octet 6th octet Vendor-assigned values CS573: Network Protocols and Standards 6 48 bit LAN Addresses OUI = Organizationally unique identifier Fixed value assigned by IEEE 224 different possibilities Not all of them are used!!! Vendor-assigned Values A total of 224 unique addresses are available by purchasing one block A block may be shared A vendor can buy more blocks with different OUIs Dec 14, 2006 CS573: Network Protocols and Standards 7 Group/Individual bit in OUI In fact, One block 225 addresses 224 of the addresses are unicast 224 of the addresses are multicast G/I bit decides if the address is multicast G/I = 0 means unicast or individual station G/I = 1 means a (LAN) multicast address 10111101 G/I (group/individual) --- first bit on the wire G/L (global/local) Dec 14, 2006 CS573: Network Protocols and Standards 8 Global/Local bit in OUI Another bit in the OUI is designated by the IEEE as G/L bit IEEE sets G/L = 0 when giving out the blocks of addresses Addresses with G/L = 1 can be used without paying IEEE but the network administrator is responsible to assign addresses such that there is no collision This leaves with 222 unique OUIs Dec 14, 2006 CS573: Network Protocols and Standards 9 Why multicast addresses? In most LANs (e.g., CSMA/CD LANs), every entity receives all the data on the LAN segment it is connected to Hardware filtering is desirable because promiscuous listening is expensive Some entities (e.g., bridges and LAN monitors) have to listen promiscuously One station will be interested in one unicast address and multiple multicast addresses Unicast address is hardwired Multicast addresses fall into hardwired hash buckets Dec 14, 2006 CS573: Network Protocols and Standards 10 Protocol Type Multiplexing One station, many higher layer protocols Which protocol is the desired recipient? Which protocol constructed the packet? IP IPX ARP XNS MAC Layer This information is also included in the LAN header --- just like LAN addresses are! Dec 14, 2006 CS573: Network Protocols and Standards 11 Protocol Type Multiplexing Original Ethernet design 2 octet long field included in LAN header 6 octets 6 octets Destination Address Source Address 2 octets Protocol Type variable Data Previously administered by Xerox, currently by IEEE Protocol vendors need to negotiate for getting a protocol type added http://standards.ieee.org/regauth/ethertype/index.html Dec 14, 2006 CS573: Network Protocols and Standards 12 SAP Multiplexing More flexible to have separate source and destination protocol type fields Can assign different numbers to the same protocol on different machines Service Access Points (SAPs) Included in 802 LAN header SSAP and DSAP Dec 14, 2006 1 octet each but only 6 bits are used CS573: Network Protocols and Standards 13 SAP Multiplexing 6 octets 6 octets 2 octets length Destination Address Source Address 2 octets variable DSAP SSAP CTL Protocol Type Data All 1’s ALL SAPs All 0’s (except G/L) data link layer itself 6-bit globally assigned SAP numbers (by IEEE) 10111101 G/I (group/individual) G/L (global/local) Dec 14, 2006 CS573: Network Protocols and Standards 14 SAP Multiplexing G/L bit is similar to the one used in LAN addresses G/I bit --- perhaps to keep compatibility with the LAN addresses??? G/I bit in LAN addresses was used to make hardware filtering convenient Hardware filtering is meaningless in SAP multiplexing Only 64 unique SAP protocols are supported Strict rules for assigning a SAP number Protocol must be designed by standard bodies Dec 14, 2006 CS573: Network Protocols and Standards 15 SAP Multiplexing Local SAP protocols can be used Network/Protocol manager’s responsibility to ensure unique SAPs to protocols Conversation startup is difficult Dec 14, 2006 SAP number at the destination machine is not known at the source machine! CS573: Network Protocols and Standards 16 SNAP SAP Subnetwork Access Protocol When DSAP = SSAP = SNAP SAP Single globally assigned SAP value AA hex (10101010) --- SNAP SAP Header is expanded to include a “protocol type” field A “longer” protocol type field can then be used Standardized to 5 octets (see book for reason!) Dec 14, 2006 CS573: Network Protocols and Standards 17 Addresses and Protocol Types LAN Addresses By using 5 octets to indicate protocol type, LAN address administration is tied to protocol type administration 1st octet 2nd octet 3rd octet Vendor code (IEEE-assigned) 4th octet 5th octet 6th octet Vendor-assigned values Protocol Type 1st octet Dec 14, 2006 2nd octet 3rd octet 4th octet 5th octet CS573: Network Protocols and Standards 18 Transmission Bit Order 802.1 defines a canonical format for LAN addresses 00-60-1D-23-20-A9 802.3 and 802.4 802.5 and FDDI LSB is transmitted first MSB is transmitted first Internetworking different topologies Bit order should be shuffled if forwarding frames between incompatible LAN topologies Dec 14, 2006 CS573: Network Protocols and Standards 19 Frame Formats Ethernet 6 octets 6 octets 2 octets Destination Address Source Address Protocol Type 802.3 Frame Format 6 octets 6 octets 2 octets length Destination Address Data Source Address 2 octets DSAP SSAP CTL Protocol Type Data Formats are compatible (Max length: 1536) Protocols are assigned values > 0600 hex (=1536) Dec 14, 2006 CS573: Network Protocols and Standards 20