Table of Contents. Layer 2. Refinement. Layer 3 view. Refinement. Devices and sublayers. Bridging and Switching

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1 Table of Contents Layer 2 Bridging and Switching Karst Koymans Informatics Institute University of Amsterdam (version 17.6, 2017/11/16 09:52:16) Friday, ovember 10, 2017 Refinement Devices and sublayers Frame formats DIX Extended Unique Identifiers Ethernet Types Bridges and Switches Basics VLAs Layered Extensions Traffic Engineering Layer 3 view Refinement H3 H2 Host B Router etwork R R2 R2 etwork B Host H3 H2

2 Refinement (with IP enabled bridges) Layer 1 and 2 devices H3 B3 R B3 H2 B R2 R2 B Layer 1 (physical) Repeaters, Hubs (multiport repeaters) Single collision domain Together they form a LA (or link) segment Layer 2 (data link) Bridges and Switches Single broadcast domain Together they form a LA (a link, usually 1 a layer 3 subnet) H3 H2 1 multi-subnet links (ok) and multi-link subnets (not so ok) also occur Layer 2 sublayer: MAC Layer 2 sublayer: LLC Media Access Control Lower data link sublayer Work from the committees Most important example is Ethernet CSMA/CD Carrier Sense, Multiple Access, with Collision Detection Backoff and Retransmission Logical Link Control Upper data link sublayer Work from the committees Introduces three new fields 2 DSAP: Destination Service Access Point SSAP: Source Service Access Point Control: 1 or 2 control bytes 2 See for a list of SAPs

3 DIX Ethernet (Ethernet II) packets/frames MAC addresses (1) Preamble SFD DstAddr SrcAddr Type PDU (with PAD) FCS Preamble and SFD 3 are handled by the physical layer (network card) A frame starts with 6 byte destination and source MAC addresses A 2 byte type field follows (multiplexing) PAD used to get a minimum PDU of 46 bytes Maximum size of PDU is 1500 bytes The Frame Check Sequence is a Cyclic Redundancy Check (CRC) 6 bytes (48 bits) MAC-48 (physical, now obsolete) EUI-48 (virtual, now including physical) EUI-64 (64-bit Extended Unique Identifier) Organizationally Unique Identifier 4 (OUI) Comprises the first three bytes of the MAC address Leaving three bytes for local assignment by the OUI-owner (In lsb first order canonical format this is 0x55 0x55 0x55 0x55 0x55 0x55 0x55 0xD5.) 4 MAC addresses (2) EUI-48 EUI-64 I/G bit: Individual (0) / Group (1) bit First bit on the wire Broadcast or multicast U/L bit: Universal (0) / Local (1) bit Second bit on the wire I/G and U/L are the Least Significant Bits (LSBs) of the first byte Sic!: this is called canonical format (LSB-format) Token Ring uses noncanonical format (MSB-format) Ample opportunity for confusion 5 Embedding of MAC-48 addresses OUI:extension OUI:FF:FF:extension Embedding of EUI-48 addresses 6 OUI:extension OUI:FF:FE:extension 00:30:65:7E:9D:5E 00:30:65:FF:FE:7E:9D:5E IPv6 is based on EUI-48 embedding for autoconfiguration but with a quirk 5 See IEEE Std , section Since MAC-48 addresses are obsolete, both FF:FF and FF:FE may be used

4 Modified EUI-64 Ethernet Types (1) The 64 bit host part of an IPv6 address Modified EUI-64 address U/L bit flipped 0030:65FF:FE7E:9D5E 0230:65FF:FE7E:9D5E The reverse happens to locally assigned IPv6 addresses 0200:0000:0000: :0000:0000:0001 which immediately explains the reason for the modification and why bits are skipped when creating IPv4-embedded IPv6 addresses Used for multiplexing Common ethertypes 0x0800 0x0806 0x8035 0x8137 0x86DD IP ARP RARP IPX (ovell) IPv6 Ethernet Types (2) frames (with LLC) Reintroducing the Ethernet Version I length field Less common ethertypes 0x0BAD Banyan Vines 0x0805 X.25 level 3 (PLP) 0x809B,0x80F3 AppleTalk 7 0x8847,0x8848 MPLS 8 0x8863,0x8864 PPPoE Preamble SFD DstAddr SrcAddr Length DSAP SSAP Ctrl LLC data (with PAD) FCS Introduces the LLC layer 2 sublayer Replaces type field by length field Used in EtherTalk packets (Apple) Disjoint values from ether types Later old DIX format also officially allowed 7 Ethertalk, AARP 8 Unicast, Multicast Ethernet 9 Discovery, Session Stage 10 In some cases Ctrl is 2 bytes and then LLC data is between 42 and 1496 bytes

5 LLC/SAP IPX frames Sub etwork Access Protocol DSAP = 0xAA SSAP = 0xAA Control = 0x03 (UI, connectionless) Adds 5 extra bytes Organization Identifier (not used, set to 0x000000) Protocol type (guess what: ether type :-)) etto effect is the waste of 8 bytes so that the PDU size (MTU) is reduced from 1500 to 1492 bytes There are four variants... DIX Ethernet with ethertype 0x SAP with protocol type 0x with DSAP = SSAP = 0xE0 Raw IPX packet starts with an (unimplemented) checksum looking like broadcast SAP DstAddr SrcAddr Length 0xFFFF Transparent Bridges Switches o-frills Copies frames between its two sides (or multiple ports) Uses Store and Forward Separates collision domains Learning and filtering Remembers on which side/port a station resides By looking (promiscuously) to all addresses Builds a filtering database Standardized in 802.1D Switches are a synonym for bridges In most cases have multiple ports Often remember on which port a station resides Switches may support more protocol extensions VLAs Quality of Service IGMP snooping Management (SMP)

6 VLAs modifications for VLAs Separating a physically bridged LA into multiple logical/virtual LAs Each VLA has its own ID Standardized as 802.1Q-2011 Ether type for VLAs: 0x8100 Conflicted with Wellfleet allocation 11 Official registration by IEEE 12 Add 4 extra bytes (VLA tag) between MAC source address and type/length field 2 bytes 0x8100 (VLA type) 3 bits priority (used by 802.1p) 1 bit CFI 13 (Ethernet/Token Ring, usually 0 (Ethernet)) 12 bits VLA ID (0-4095) Related to the MSB-LSB-format issue: Canonical Format Indicator. Later replaced by DEI (Drop Eligible Indicator). VLA membership Provider Bridges (PBs) ested VLAs Port based Easy; static MAC based Administrative burden; dynamic Protocol and IP address based Wrong layer; not transparent Standardized as 802.1ad Several non-standard Q-in-Q schemes Add a Service-VLA-tag (S-tag; outer tag) in front of the Customer-VLA-tag (C-tag; inner tag) Used by a PB (Provider Backbone etwork) Ether type for S-VLAs: 0x88A8 (now also in IAA list) Separates backbone VLA assignments from customer VLA assignments Placed between source MAC address and customer VLA tag

7 Provider Backbone Bridges (PBBs) MAC-in-MAC or M-in-M PBB-TE Provider Backbone Bridges Traffic Engineering Standardized as 802.1ah Adds a complete second Ethernet header with extended tags Used by a PBB (Provider Backbone Bridging etwork) Adds provider backbone MAC destination and source addresses Followed by a Backbone tag (B-tag) Ether type for B-tags is again 0x88A8 (same as S-tag) And a new Backbone Service Instance tag (I-Tag) Ether type for I-tags is 0x88E7 (in IAA list 2017) Contains 1 byte flags and a 3 byte Service Instance Identifier (I-SID) Formally encapsulates the client MAC destination and source address Derived from PBT (Provider Backbone Transport; ortel) Connection oriented Ethernet transport Standardized as 802.1Qay IEEE alternative for MPLS-TP (MPLS Transport Profile; ITU) which is based on T-MPLS (Transport MPLS) 802.1Q-2011 standard 14 includes 802.1ad, 802.1ah and 802.1Qay 14 aming explained in TRILL TRansparent Interconnect of Lots of Links SPB Shortest Path Bridging Defines RBridges Routing on layer 2 Smart bridges, interoperable with 802.1D and 802.1Q Independent, localized routing in a single LA Uses layer 3 like headers with hop count Problem and applicability statement in RFC 5556 (May 2009) Specification in RFC 6325 (July 2011), 7176, 7177 (May 2014) Standardized as 802.1aq (approved in March 2012) It replaces old spanning tree mechanisms, like STP, RSTP, MSTP It supports two flavours SPBV (forwarding 802.1ad Q-in-Q frames) SPBM (forwarding 802.1ah M-in-M frames)

8 etwork programmability Software Defined etworking (SD) RFC 7426 Dynamic programmable network control and management etwork Function(s) Virtualization (FV) Using virtualization to implement network services all left to Advanced etworking (A)

Layer 2. Bridging and Switching. Karst Koymans. Informatics Institute University of Amsterdam. (version 16.4, 2017/02/15 12:07:08)

Layer 2. Bridging and Switching. Karst Koymans. Informatics Institute University of Amsterdam. (version 16.4, 2017/02/15 12:07:08) Layer 2 Bridging and Switching Karst Koymans Informatics Institute University of Amsterdam (version 16.4, 2017/02/15 12:07:08) Friday, February 17, 2017 Karst Koymans (UvA) Layer 2 Friday, February 17,