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Ethernet

Ethernet. frame. frame. Direct connection: point-to-point. 2 nodes:. datagram. rcving node. link layer protocol. sending node. adapter (NIC). adapter (NIC). More than 2 nodes?. Direct connection: broadcast. Shared media. Metcalfe’s Ethernet Sketch (1973).

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Ethernet

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  1. Ethernet

  2. frame frame Direct connection: point-to-point • 2 nodes: datagram rcving node link layer protocol sending node adapter (NIC) adapter (NIC) • More than 2 nodes?

  3. Direct connection: broadcast • Shared media Metcalfe’s Ethernet Sketch (1973) Ethernet “dominant” LAN technology: • cheap $30 for 100Mbs! • first widely used LAN technology • simpler, cheaper than token LANs and ATM • kept up with speed race: 10, 100, 1000 Mbps

  4. Ethernet Format: Physical Layer • Each bit has a transition • Allows clocks in sending and receiving nodes to synchronize to each other • no need for a centralized, global clock among nodes!

  5. Ethernet Format: Framing • Preamble: (clearing your throat) • 8 bytes, allows sender/receiver clocks to synchronize • Destination/SourceAddress: (hey Paul, Tom here) • 6 bytes each • Type: • 2 bytes, indicates higher layer protocol • 0x0800 is IP, 0x0806 is ARP • Data: 46-1500 bytes • FCS (CRC): • catches most transmission errors - errored frames dropped

  6. Ethernet Packet Structure • 14 byte header • 2 addresses Graphic Source: Network Computing Magazine August 7, 2000

  7. Ethernet Physical Layer Packet Structure • 8 byte header (Preamble) Graphic Source: Network Computing Magazine August 7, 2000

  8. Ethernet Addressing • 6 byte address (unique to each adapter) • Example: 08-0b-db-e4-b1-02 • 2^48 = 281 trillion; can produce 100 million LAN devices every day for 2000 years! • Interpretation of address: • Upper 24 bits OUI (Organizationally Unique Identifier) • Lower 24 bits Organization-assigned portion • Unicast: lowest bit of first byte is 0 • Multicast: lowest bit of first byte is 1 • Broadcast: ff-ff-ff-ff-ff-ff • Adaptor accept frame if and only if: • Destination address matches adapter address, or • Destination address is broadcast, or • Destination address is multicast and adapter has been configured to accept it

  9. CSMA/CD (the polite conversationalist) carrier sense: don’t transmit if you sense someone else transmitting collision detection: abort your transmission if you sense someone else transmitting random access: wait random time before attempting a retransmission Ethernet Media sharing

  10. nodes hub Ethernet Technologies • 10Base2: • 10Mbps, 200 meters max cable length • thin coaxial cable in a bus topology • repeaters connect multiple segments • 10BaseT / 100BaseT “fast ethernet”: • 10/100Mbps, Twisted pair • Nodes connect to a hub in “star topology” • Gigabit Ethernet: • 1Gbps, fibre or copper • Extending from LAN to MAN • 10 Gbps Ethernet now! • High data speed + larger distance + increasing number of devices per LAN => switching

  11. Twisted Pair Wire Map • EIA/TIA 568B (UGA Standard)

  12. Standard vs Crossover Cables Card-to-Hub Wiring (Standard Cable) RD+ TD+ TD- RD- RD+ TD+ TD- RD- Card-to-Card (Hub-to-Hub) Wiring (Crossover Cable) TD+ (RD+) TD+ (RD+) TD- (RD-) TD- (RD-) RD+ (TD+) RD+ (TD+) RD- (TD-) RD- (TD-)

  13. Power over Ethernet (PoE) http://www.nwfusion.com/news/2003/1124infrapoe.html

  14. Most popular LAN technology nowadays 10Mb/s - 1Gb/s Each host has unique 48bit MAC address (factory assigned) Frames sent to MAC addresses Broadcasts widely used To find destination MAC address, ARP protocol is used IP: 10.0.0.10 MAC: 00:00:aa:aa:aa:aa IP: 10.0.0.11 MAC: 00:00:bb:bb:bb:bb A B IP: 10.0.0.12 MAC: 00:00:cc:cc:cc:cc IP: 10.0.0.13 MAC: 00:00:dd:dd:dd:dd C D Ethernet frame Dest MAC Source MAC IP packet DestIP SourceIP Data Ethernet

  15. ARP Query Host A Host B Broadcast Host B MAC ? Host B IP ARP Response Unicast Host B MAC Host B IP ARP: finding the MAC Address RFC 826: Address Resolution Protocol, 1982

  16. ARP frame format

  17. 32-bit Class D IP Address 1110 Low-order 23 bits of multicast Group ID copied to Enet address 00000001 00000000 01011110 0 48-bit Ethernet Address IP & Ethernet Multicast Address Mapping • IP multicast addresses (class D) range from 224.0.0.1 to 239.255.255.255 and map to Ethernet destination MAC addresses as shown below

  18. high byte Multicast(1) Local(1)/global(0) administration 48 bit address Multicast Addresses • Multicast revises addresses to be protocol specific: high byte, least bit is “1” if multicast. • Applications that use multicast • Imagecast • AppleTalk zones • One-to-many IP video broadcasting • Service location protocol (SLP)

  19. IGMP Snooping • Internet Group Management Protocol (IGMP - RFC 2236) used to manage IP multicast traffic • Application wishing to receive traffic for specific IP multicast address sends out an ICMP join request (or a leave request to stop receiving multicast) • Switches that employ IGMP snooping listen for IGMP join/leave requests to decide when to send a specific multicast frame to a port

  20. Switching (same as Bridging) • Goals • traffic isolation • “transparent” operation • plug-and-play • Operation • store and forward Ethernet frames • examine frame header and selectively forward frame based on MAC dest address • when frame is to be forwarded on segment, uses CSMA/CD to access segment

  21. E0: 0260.8c01.1111 E0: 0260.8c01.2222 E1: 0260.8c01.3333 E1: 0260.8c01.4444 0260.8c01.1111 0260.8c01.3333 E0 E1 0260.8c01.2222 0260.8c01.4444 Switching Tables

  22. X Y Segment 1 Broadcast Segment 2 Spanning Tree Protocol

  23. Spanning tree protocol (IEEE 802.1d) • Every bridge has bridge-id • bridge-id = 2-byte priority + 6-byte MAC addr • Question: MAC address of bridge?? • Every port of bridge has • port-id = 1-byte priority + 1-byte port-number • port-cost = inversely proportional to link speed • Bridge with lowest bridge-id is root bridge • On each LAN segment, bridge with lowest path cost to root is designated bridge (use bridge-id and port-id to break ties) • A bridge forwards frames through a port only if it is a designated bridge for that LAN segment

  24. STP terminology • Port roles: • Root port (switch port leading to root) • Designated port (LAN port leading to root) • Alternate / backup port (anything else) • Port states: • Blocking (no send/rcv, except STP bpdus) • Listening (prepare for learning/forwarding) • Learning (learn MAC addr but no forwarding) • Forwarding (send/rcv frames) • Can disable STP on port or switch • All frames are forwarded • BPDUs?

  25. STP operation • BPDU carries 4-tuple: • <root-id, root-cost, bridge-id, port-id> • Store rcvd and send 4-tuple for each port: • port with best rcvd 4-tuple is root port • root bridge has no such port • if send 4-tuple better than rcv 4-tuple, port is designated port • rest of the ports are alternate/backup ports • Various timers

  26. Spanning tree example DP DP DP RP DP RP RP DP DP DP DP DP root RP DP DP

  27. New Spanning Tree Protocol versions • Implementation of : • Rapid Spanning Tree Protocol 802.1w (RSTP); • Per VLAN Spanning Tree 802.1q (PVST +); • Multiple Spanning Tree 802.1s (MST); • Load balancing across links; • BPDU guard; • Root Guard; and • Uni-Directional Link Detection (UDLD)

  28. Evolution of Spanning Tree The following developments in Spanning Tree Protocol are examined: • Per-VLAN Spanning Tree (PVST) is a Cisco-proprietary implementation requiring ISL trunk encapsulation. • PVST+ provides Layer 2 load balancing for the VLAN on which it runs. • MST (IEEE 802.1s) extends the IEEE 802.1w Rapid Spanning Tree (RST) algorithm to multiple spanning-trees. • Enhanced PVST + or Multiple Instance of Spanning Tree Protocol (MISTP), a compromise between PVST+ and MST.

  29. 802.1w Rapid Spanning Tree Protocol • The IEEE 802.1w specification, Rapid Spanning Tree Protocol, provides for subsecond reconvergence of STP after failure of one of the uplinks in a bridged environment. • 802.1w provides the structure on which the 802.1s features such as multiple spanning tree operates. • There are only three port states left in RSTP corresponding to the three possible operational states Learning ,Forwarding and Discarding. • Rapid Transition to Forwarding State is the most important feature introduced by 802.1w: • RSTP actively confirms safe port transition to forwarding without relying on timers; • There is now a real feedback mechanism that takes place between RSTP-compliant bridges. • In order to achieve fast convergence on a port, the protocol relies upon two new variables: edge ports and link type.

  30. Virtual LANs • LAN (broadcast domain) grows large • “departments” or “workgroups” not happy with big broadcast domain • Security (eavesdropping) • Bandwidth consumed by flooding/multicasting • Split LAN into multiple broadcast domains • Multiple physical LANs? • Too expensive! • People move all the time! • VLAN: logical partition of LAN

  31. Virtual LANs

  32. VLANs: IEEE 802.1q destination addr source addr data FCS type • “Tagged” Ethernet frames contain VLAN-id • Switch adds/removes tag when forwarding frames between trunk and non-trunk ports • Complications: • Hosts and legacy switches do not understand VLAN tags • Tag insertion/removal requires FCS recomputation • Frame length increases beyond legacy MTU 3-bit priority 1-bit CFI 12-bit VLAN id VLAN protocol id = 0x8100

  33. VLAN Standard: IEEE 802.1q CFI-Canonical Format Identifier (Ethernet/TokenRing)

  34. The 802.3 (legacy) and 802.1Q Ethernet frame formats

  35. L2 Tunneling The default system MTU for traffic on the switch is 1500 bytes. You can configure the switch to support larger frames by using the system mtu global configuration command. Because the 802.1Q tunneling feature increases the frame size by 4 bytes when the metro tag is added, you must configure all switches in the service-provider network to be able to process larger frames by increasing the switch system MTU size to at least 1504 bytes. The maximum allowable system MTU for Catalyst 3550 Gigabit Ethernet switches is 2000 bytes; the maximum system MTU for Fast Ethernet switches is 1546 bytes.

  36. Some Switches Support Priorities

  37. VLAN/802.1p Switch FS Internal Queues: FS VS VS VS p7: p0: FS FS VS VS VS L2 Switch VS VS 802.1p Prioritization • Eight levels of prioritization - p0 (lowest) through p7 (highest) • 802.1p example

  38. 8 Bytes 6 Bytes 6 Bytes 2 Bytes 46-1500 Bytes 4 Bytes Frame Check Sequence Preamble /SFD Destination Address Source Address Type/Length Field Data and Padding Cut-through forwards after destination address Modified cut-through forwards after 64 bytes of data Store-and-forward forwards after FCS Store&Forward vs Cut Through Switching • The following diagram depicts the differences between store-and-forward and cut-through switching • Switches should employ store-and-forward exclusively (cut-through propagates bad packets)

  39. Gigabit Ethernet over Fiber

  40. Wave Division Multiplexing DWDM 1528 to 1560 nm: erbium doped fiber amplifiers (EDFA) EDFA every 60km, regeneration every 500km

  41. Input Coupler Isolator 1480 or 980 nm Pump Laser Output Erbium Doped Fiber Erbium doped fiber amplifiers • A pump laser injects a high intensity pulse of light exciting the erbium and causing the erbium atoms to release their stored energy. • The EDFA amplifies all the wavelengths to the same level (gain flatness). • DWDM 1528 to 1560 nm: EDFA every 60km, regeneration every 500km

  42. interface GigabitEthernet2/9 description NISN/NASA mtu 9216 no ip address speed nonegotiate switchport switchport trunk encapsulation dot1q switchport trunk allowed vlan 210-213,217-226,231,232 switchport mode trunk switchport nonegotiate interface GigabitEthernet2/10 description GEMnet mtu 9216 no ip address speed nonegotiate switchport switchport trunk encapsulation dot1q switchport trunk allowed vlan 167-169,231 switchport mode trunk switchport nonegotiate Configuration Example WKN 20040414

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