Bridging and Switching. Karst Koymans. Monday, February 17, 2014

Transcription

1 .. Layer 2 Bridging and Switching Karst Koymans Informatics Institute University of Amsterdam (version 3.7, 2014/02/19 19:50:51) Monday, February 17, 2014 Karst Koymans (UvA) Layer 2 Monday, February 17, / 39

2 .1 Refinement.2 Devices and sublayers.3 Frame formats DIX Extended Unique Identifiers Ethernet Types Bridges and Switches Basics VLANs Layered Extensions Traffic Engineering Karst Koymans (UvA) Layer 2 Monday, February 17, / 39

3 Refinement Outline.1 Refinement.2 Devices and sublayers.3 Frame formats DIX Extended Unique Identifiers Ethernet Types Bridges and Switches Basics VLANs Layered Extensions Traffic Engineering Karst Koymans (UvA) Layer 2 Monday, February 17, / 39

4 Layer 3 view Host Network Router Network Host.

5 Refinement H3 R H2 B R2 R2 B N N N H3. H2 N

6 Refinement (with IP enabled bridges) H3 B3 R B3 H2 B R2 R2 B N N N H3. H2 N

7 Devices and sublayers Outline.1 Refinement.2 Devices and sublayers.3 Frame formats DIX Extended Unique Identifiers Ethernet Types Bridges and Switches Basics VLANs Layered Extensions Traffic Engineering Karst Koymans (UvA) Layer 2 Monday, February 17, / 39

8 Devices and sublayers Layer 1 and 2 devices Layer 1 (physical) Repeaters, Hubs (multiport repeaters) Single collision domain Together they form a LAN (or link) segment Layer 2 (data link) Bridges and Switches Single broadcast domain Together they form a LAN (a link, usually 1 a layer 3 subnet) 1 multi-link subnets and multi-subnet links also occur Karst Koymans (UvA) Layer 2 Monday, February 17, / 39

9 Devices and sublayers Layer 2 sublayer: MAC 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 Karst Koymans (UvA) Layer 2 Monday, February 17, / 39

10 Devices and sublayers Layer 2 sublayer: LLC Logical Link Control Upper data link sublayer Work from the committees Introduces three new fields DSAP: Destination Service Access Point SSAP: Source Service Access Point Control: 1 or 2 control bytes Karst Koymans (UvA) Layer 2 Monday, February 17, / 39

11 Frame formats Outline.1 Refinement.2 Devices and sublayers.3 Frame formats DIX Extended Unique Identifiers Ethernet Types Bridges and Switches Basics VLANs Layered Extensions Traffic Engineering Karst Koymans (UvA) Layer 2 Monday, February 17, / 39

12 Frame formats DIX Outline.1 Refinement.2 Devices and sublayers.3 Frame formats DIX Extended Unique Identifiers Ethernet Types Bridges and Switches Basics VLANs Layered Extensions Traffic Engineering Karst Koymans (UvA) Layer 2 Monday, February 17, / 39

13 Frame formats DIX DIX Ethernet packets/frames Also known as Ethernet II packets/frames Preamble SFD DstAddr SrcAddr Type PDU (with PAD) FCS Preamble and SFD 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 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) Karst Koymans (UvA) Layer 2 Monday, February 17, / 39

14 Frame formats DIX MAC addresses (1) 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 2 (OUI) Comprises the first three bytes of the MAC address Leaving three bytes for local assignment by the OUI-owner 2 Karst Koymans (UvA) Layer 2 Monday, February 17, / 39

15 Frame formats DIX MAC addresses (2) 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 3 3 See IEEE Std , section 9.5 Karst Koymans (UvA) Layer 2 Monday, February 17, / 39

16 Frame formats Extended Unique Identifiers Outline.1 Refinement.2 Devices and sublayers.3 Frame formats DIX Extended Unique Identifiers Ethernet Types Bridges and Switches Basics VLANs Layered Extensions Traffic Engineering Karst Koymans (UvA) Layer 2 Monday, February 17, / 39

17 Frame formats Extended Unique Identifiers EUI-48 EUI-64 Embedding of MAC-48 addresses OUI:extension OUI:FF:FF:extension Embedding of EUI-48 addresses 4 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... 4 Since MAC-48 addresses are obsolete, both FF:FF and FF:FE may be used Karst Koymans (UvA) Layer 2 Monday, February 17, / 39

18 Frame formats Extended Unique Identifiers Modified EUI-64 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 same happens to locally assigned IPv6 addresses 0200:0000:0000: :0000:0000:0001 which immediately explains the reason for the modification Karst Koymans (UvA) Layer 2 Monday, February 17, / 39

19 Frame formats Ethernet Types Outline.1 Refinement.2 Devices and sublayers.3 Frame formats DIX Extended Unique Identifiers Ethernet Types Bridges and Switches Basics VLANs Layered Extensions Traffic Engineering Karst Koymans (UvA) Layer 2 Monday, February 17, / 39

20 Frame formats Ethernet Types Ethernet Types (1) Used for multiplexing. Common ethertypes.. 0x0800 0x0806 0x8035 0x8137 0x86DD IP ARP RARP IPX (Novell) IPv6 Karst Koymans (UvA) Layer 2 Monday, February 17, / 39

21 Frame formats Ethernet Types Ethernet Types (2). Less common ethertypes. 0x0BAD 0x0805 0x809B,0x80F3 0x8847,0x8848 0x8863,0x8864 Banyan Vines X.25 level 3 (PLP) AppleTalk a MPLS b PPPoE c a Ethertalk, AARP b Unicast, Multicast Ethernet. c Discovery, Session Stage Karst Koymans (UvA) Layer 2 Monday, February 17, / 39

22 Frame formats Outline.1 Refinement.2 Devices and sublayers.3 Frame formats DIX Extended Unique Identifiers Ethernet Types Bridges and Switches Basics VLANs Layered Extensions Traffic Engineering Karst Koymans (UvA) Layer 2 Monday, February 17, / 39

23 Frame formats frames (with LLC) Reintroducing the Ethernet Version I length field 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 5 In some cases Ctrl is 2 bytes and then LLC data is between 42 and 1496 bytes Karst Koymans (UvA) Layer 2 Monday, February 17, / 39

24 Frame formats LLC/SNAP Sub Network 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 :-)) Netto effect is the waste of 8 bytes so that the PDU size (MTU) is reduced from 1500 to 1492 bytes Karst Koymans (UvA) Layer 2 Monday, February 17, / 39

25 Frame formats IPX frames There are four variants... DIX Ethernet with ethertype 0x SNAP with protocol type 0x with DSAP = SSAP = 0xE0 Raw IPX packet starts with an (unimplemented) checksum looking like broadcast SAP DstAddr SrcAddr Length 0xFFFF... Karst Koymans (UvA) Layer 2 Monday, February 17, / 39

26 Bridges and Switches Outline.1 Refinement.2 Devices and sublayers.3 Frame formats DIX Extended Unique Identifiers Ethernet Types Bridges and Switches Basics VLANs Layered Extensions Traffic Engineering Karst Koymans (UvA) Layer 2 Monday, February 17, / 39

27 Bridges and Switches Basics Outline.1 Refinement.2 Devices and sublayers.3 Frame formats DIX Extended Unique Identifiers Ethernet Types Bridges and Switches Basics VLANs Layered Extensions Traffic Engineering Karst Koymans (UvA) Layer 2 Monday, February 17, / 39

28 Bridges and Switches Basics Transparent Bridges No-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 Karst Koymans (UvA) Layer 2 Monday, February 17, / 39

29 Bridges and Switches Basics Switches 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 VLANs Quality of Service Management (SNMP) Karst Koymans (UvA) Layer 2 Monday, February 17, / 39

30 Bridges and Switches VLANs Outline.1 Refinement.2 Devices and sublayers.3 Frame formats DIX Extended Unique Identifiers Ethernet Types Bridges and Switches Basics VLANs Layered Extensions Traffic Engineering Karst Koymans (UvA) Layer 2 Monday, February 17, / 39

31 Bridges and Switches VLANs VLANs Separating a physically bridged LAN into multiple logical/virtual LANs Each VLAN has its own ID Standardized as 802.1Q-2011 Ether type for VLANs: 0x8100 Conflicted with Wellfleet allocation 6 Official registration by IEEE Karst Koymans (UvA) Layer 2 Monday, February 17, / 39

32 Bridges and Switches VLANs modifications Add 4 extra bytes (VLAN tag) between MAC source address and type/length field 2 bytes 0x8100 (VLAN type) 3 bits priority (used by 802.1p) 1 bit CFI 8 (Ethernet/Token Ring, usually 0 (Ethernet)) 12 bits VLAN ID (0-4095) 8 Related to the MSB-LSB-format issue: Canonical Format Indicator. Later replaced by DEI (Drop Eligible Indicator). Karst Koymans (UvA) Layer 2 Monday, February 17, / 39

33 Bridges and Switches VLANs VLAN membership Port based Easy; static MAC based Administrative burden; dynamic Protocol and IP address based Wrong layer; not transparent... Karst Koymans (UvA) Layer 2 Monday, February 17, / 39

34 Bridges and Switches Layered Extensions Outline.1 Refinement.2 Devices and sublayers.3 Frame formats DIX Extended Unique Identifiers Ethernet Types Bridges and Switches Basics VLANs Layered Extensions Traffic Engineering Karst Koymans (UvA) Layer 2 Monday, February 17, / 39

35 Bridges and Switches Layered Extensions Provider Bridges (PBs) Nested VLANs Standardized as 802.1ad Several non-standard Q-in-Q schemes Add a Service-VLAN-tag (S-tag; outer tag) in front of the Customer-VLAN-tag (C-tag; inner tag) Used by a PBN (Provider Backbone Network) Ether type for S-VLANs: 0x88a8 (not in IANA list) Separates backbone VLAN assignments from customer VLAN assignments Placed between source MAC address and customer VLAN tag Karst Koymans (UvA) Layer 2 Monday, February 17, / 39

36 Bridges and Switches Layered Extensions Provider Backbone Bridges (PBBs) MAC-in-MAC or M-in-M Standardized as 802.1ah Adds a complete second Ethernet header with extended tags Used by a PBBN (Provider Backbone Bridging Network) 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 (not in IANA list) Contains a 24 bit Service Instance Identifier Formally includes the client MAC destination and source address Karst Koymans (UvA) Layer 2 Monday, February 17, / 39

37 Bridges and Switches Traffic Engineering Outline.1 Refinement.2 Devices and sublayers.3 Frame formats DIX Extended Unique Identifiers Ethernet Types Bridges and Switches Basics VLANs Layered Extensions Traffic Engineering Karst Koymans (UvA) Layer 2 Monday, February 17, / 39

38 Bridges and Switches Traffic Engineering PBB-TE Provider Backbone Bridges Traffic Engineering Derived from PBT (Provider Backbone Transport; Nortel) 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 includes 802.1ad, 802.1ah and 802.1Qay Karst Koymans (UvA) Layer 2 Monday, February 17, / 39

39 Bridges and Switches Traffic Engineering TRILL TRansparent Interconnect of Lots of Links Defines RBridges Routing on layer 2 Smart bridges, interoperable with 802.1D and 802.1Q Independent, localized routing in a single LAN Uses layer 3 like headers with hop count Problem and applicability statement in RFC 5556 Specification in RFC (July 2011) Karst Koymans (UvA) Layer 2 Monday, February 17, / 39

40 Bridges and Switches Traffic Engineering SPB Shortest Path Bridging 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) Karst Koymans (UvA) Layer 2 Monday, February 17, / 39