An Engineering guide to IEEE 802.1Q and IEEE 802.1p Silvano Gai - PowerPoint PPT Presentation

An Engineering guide to IEEE 802.1Q and IEEE 802.1p Silvano Gai 1/6/99 Silvano Gai - 1998 1

Agenda • VLAN • IEEE 802 committees • IEEE 802.1p • IEEE 802.1Q • The Cisco solution 1/6/99 Silvano Gai - 1998 2

Compass • VLAN N assigning frames to VLANs N tagging and baby giant frames N spanning tree(s) N access or independent VLANs N single/multiple filtering data base(s) N internetworking between VLANs • IEEE 802 committees • IEEE 802.1p • IEEE 802.1Q • The Cisco solution 1/6/99 Silvano Gai - 1998 3

Assigning frames to VLANs • A station may be member of one or more VLANs • Membership may be: N static I per port N dynamic I per MAC address I per protocol I per layer 3 address I per multicast address I “policy-based” (per application, per user, etc.) 1/6/99 Silvano Gai - 1998 4

Frame tagging • The tag contains the VLAN membership information • Implicit tagging N no tag is added to the frame N easy in connection-oriented approaches N difficult for multicast/broadcast frames • Explicit tagging N a tag is added to each frame N the tag carries the VLAN membership information N the tag may carry additional information 1/6/99 Silvano Gai - 1998 5

Baby Giants • The addition of extra bytes for the tag makes frames “Baby Giants” • How to accommodate the extra bytes for the tag in the frame? N 802.1 is persuading 802.3 to increase the maximum frame size from 1518 to 1522 (4 extra bytes) 1/6/99 Silvano Gai - 1998 6

Explicit tagging • Where to position the tag in the frame? • Two possibilities: N One level tagging I also called “Internal tagging” N Two level tagging I also called “External tagging” • Both require to be implemented in ASIC for wire speed performance 1/6/99 Silvano Gai - 1998 7

One level tagging • The original frame is modified with the addition of the tag inside the frame • The tagged frame has a valid format also for the “VLAN unaware”devices N MAC SA and DA are unchanged N an exception: it may be a baby giant 1/6/99 Silvano Gai - 1998 8

Example of one level tagging • Tagging Ethernet - IEEE 802.3 New Field Ethernet v2.0 PREAM. SFD DA SA TAG PT DATA FCS Octets 7 1 6 6 4 2 from 46 to 1500 4 PREAM. SFD DA SA TAG LEN. LLC PDU PAD FCS IEEE 802.3 1/6/99 Silvano Gai - 1998 9

Two-level tagging • The original frame is left unchanged • A new external header is added in front of the original frame N New SA, DA, (RIF), Ethertype, and VLAN-ID N It is possible to support giant frames • The RIF works better: N two-level tagging is a tunnelling mechanism N it is unclear how source routing works in 1Q • A Tricky FCS fix-up in the new header would allow original frame FCS to be retained 1/6/99 Silvano Gai - 1998 10

Inter-Switch Link (ISL) • Original frame is encapsulated with ISL header and FCS, i.e. two level tagging • Support up to 1,024 VLANs • Implemented in ASICs provides wire speed performance ISL Header FCS Encapsulated frame 1 ... 24.5 KBytes 26 bytes 4 bytes 1/6/99 Silvano Gai - 1998 11

ISL Header Format Destination MAC address DA Type User SA LEN AAAA03 HSA VLAN BPDU INDEX RES 01-00-0c-00-00 • The higher 40 bit - multicast destination address • Lowest 8 bits used by type and user field 1/6/99 Silvano Gai - 1998 12

Spanning Tree • Three different possibilities: N Single spanning tree N Per VLAN spanning tree N Shared spanning tree • Single spanning tree does not allow: N multiple active topologies N load balancing • Cisco implements one spanning tree per VLAN, at present 1/6/99 Silvano Gai - 1998 13

Multiple Spanning Trees • All links in the network are simultaneously used S1 S2 S3 Red ST Green ST 1/6/99 Silvano Gai - 1998 14

What is a VLAN? • Two possible models N Access VLANs I VLANs are a clever way to specify filters to limit endstation-to-endstation connectivity on a single, bridged LAN N Independent VLANs I VLANs are a clever way to utilize one physical plant to carry multiple, independent bridged LANs 1/6/99 Silvano Gai - 1998 15

Access VLANs • It is a single bridged LAN, with filters N filtering helps in scaling somewhat larger • Access VLANs require a single spanning tree for the whole network, because they have one filtering database for all VLANs in each bridge 1/6/99 Silvano Gai - 1998 16

Access VLANs • One-way VLANs N Half-duplex conversations between different VLANs N Bridge 1 never sees F’s source on yellow or blue, nor X’s or Y’s sources on green N Filtering database must ignore “color” F F X X 1 1 2 2 Y Y 1/6/99 Silvano Gai - 1998 17

Independent VLANs • It is possible to build large networks N if the scope of each VLAN is not global N routers plus bridged LANs are known to scale well • Per VLAN filtering database • They work with: N a single spanning tree N one spanning tree per VLAN N multiple VLANs in each of several spanning trees 1/6/99 Silvano Gai - 1998 18

Independent VLANs • They support duplicate MAC addresses N DECNet phase IV routers and two-Ethernet Sun workstations N to route some protocols and bridge others R1 (Route IP) X Bridge NetBEUI Y X S1 S2 Y X Y When R1 bridges some protocol between X and Y on different VLANs, S1 and S2 see duplicate MAC addresses for Y and X. 1/6/99 Silvano Gai - 1998 19

Number of “filtering databases” • MFD/SE N Multiple Filtering Database - Single Entry N Natural solution for independent VLANs N Compatible with multiple spanning trees • SFD/ME N Single Filtering Database - Multiple Entry N Solution adopted in Access VLAN to try to support duplicated MAC addresses N Requires a single spanning tree • Duplicate MAC addresses are common!!! 1/6/99 Silvano Gai - 1998 20

Internetworking between VLANs • Using routers N classical approach N scale well • Layer 2 shortcuts N switches create shortcuts between VLANs N limited scalability 1/6/99 Silvano Gai - 1998 21

Compass • VLAN • IEEE 802 committees N IEEE 802.1 N IEEE 802.3ac N standard tagging scheme • IEEE 802.1p • IEEE 802.1Q • The Cisco solution 1/6/99 Silvano Gai - 1998 22

IEEE 802 LMSC • 802 LAN/MAN Standards Committee N 802.1: Higher Layer Interfaces (*) I 802.1D (transparent bridging) I 802.1G (metro transparent bridging) I 802.1H (translation bridging) I 802.1D Reaffirmation I 802.1p Priorities/GARP/GMRP I 802.1Q VLANs/GVRP N 802.3: CSMA/CD (Ethernet) I 802.3ac N 802.5: Token Ring N Others (*) IEEE 802.1 started working on VLANs in late 1995 and it has still not finished 1/6/99 Silvano Gai - 1998 23

IEEE 802.3ac • IEEE Standards for Local and Metropolitan Area Networks: N Supplement to Carrier Sense Multiple Access with Collision Detection (CSMA/CD) Access Method & Physical Layer Specification I Frame Extension for Virtual Bridged Local Area Networks (VLAN) Tagging on 802.3 Networks. • Draft 1 • Main topic: N Extend Maximum Frame size from 1518 to 1522 octets 1/6/99 Silvano Gai - 1998 24

Tagging scheme 6 Destination Address 3 1 user 6 CFI Source Address priority 2 EtherType = TPID VID (VLAN ID) - 12 bits 2 Tag Control Information 2 MAC Length/Type Used in: � IEEE 802.3ac 42 MAC DATA � IEEE 802.1Q - � IEEE 802.1p 1500 PAD FCS 4 1/6/99 Silvano Gai - 1998 25

One-level tagging • Insert Ethertype and VLAN-ID after MAC source (or RIF), but before original Ethertype/Length (or LLC) • Includes T-R Encapsulation bit so that T-R frames can be carried across Ethernet backbones without 802.1H translation of data contents • 802.1p and 802.1Q share the same tag 1/6/99 Silvano Gai - 1998 26

802.1p/Q tags Dest Src Len/Etype Data FCS Recompute FCS 6 6 2 2 2 ... 4 Dest Src Etype p/Q Label Len/Etype Data FCS VLAN-ID and T-R Priority VLAN-ID Encaps Flag are .1Q, not .1p Token-Ring Encapsulation Flag 1/6/99 Silvano Gai - 1998 27

Compass • VLAN • IEEE 802 committees • IEEE 802.1p N Expedited traffic capabilities N Bridge architecture N GARP, GMRP • IEEE 802.1Q • The Cisco solution 1/6/99 Silvano Gai - 1998 28

IEEE 802.1p • IEEE Standards for Local and Metropolitan Area Networks: N Supplement to Media Access Control (MAC) bridges: Traffic Class Expediting and Dynamic Multicast Filtering • Draft 8 • Two main topics: N Expedited traffic capabilities N Filtering services to support the dynamic use of Group MAC addresses 1/6/99 Silvano Gai - 1998 29

Expedited traffic capabilities • Priority labeling N MAC-layer priority in the add-on tag N Priority not derived from MAC address • Multiple output queues per output port N output queue selection based on 802.1p tag N maintains ordering only between frames at same priority • 802.1 is cooperating with IETF’s ISSLL (Integrated Services over Specific Lower Layers) N mapping L3 RSVP requests to 802.1p priorities via a subnet bandwidth manager 1/6/99 Silvano Gai - 1998 30

Bridge architecture Source Port Destination Port Filtering State Information State Information Database 3.7.1 3.7.2 3.7.3 Queues 3.7.4 3.7.5 3.7.6 Frame reception Frame discarding Frame transmission 3.7.1 Enforcing topology restriction 3.7.4 Selecting frames for transmission 3.7.2 Filtering Frames 3.7.5 Mapping priority 3.7.3 Queueing Frames 3.7.6 Recalculating FCS 1/6/99 Silvano Gai - 1998 31