an engineering guide to ieee 802.1q and ieee...

1Silvano Gai - 19981/6/99

An Engineering guideto IEEE 802.1Q andIEEE 802.1p

Silvano Gai


• VLAN

• IEEE 802 committees

• IEEE 802.1p

• IEEE 802.1Q

• The Cisco solution

Agenda


• VLANu assigning frames to VLANsu tagging and baby giant framesu spanning tree(s)u access or independent VLANsu single/multiple filtering data base(s)u internetworking between VLANs


• IEEE 802.1p

• IEEE 802.1Q


Compass


Assigning frames to VLANs• A station may be member of one or

more VLANs

• Membership may be:u static

n per portu dynamic

n per MAC addressn per protocoln per layer 3 addressn per multicast addressn “policy-based” (per application, per user,

etc.)


Frame tagging• The tag contains the VLAN membership

information

• Implicit taggingu no tag is added to the frameu easy in connection-oriented approachesu difficult for multicast/broadcast frames

• Explicit taggingu a tag is added to each frameu the tag carries the VLAN membership

informationu the tag may carry additional information


Baby Giants• The addition of extra bytes for the tag

makes frames “Baby Giants”

• How to accommodate the extra bytesfor the tag in the frame?

u 802.1 is persuading 802.3 to increase themaximum frame size from 1518 to 1522 (4extra bytes)


Explicit tagging• Where to position the tag in the frame?

• Two possibilities:u One level tagging

n also called “Internal tagging”u Two level tagging

n also called “External tagging”

• Both require to be implemented inASIC for wire speed performance


One level tagging• The original frame is modified with the

addition of the tag inside the frame

• The tagged frame has a valid formatalso for the “VLAN unaware”devices

u MAC SA and DA are unchangedu an exception: it may be a baby giant


Example of one level tagging

LEN. LLC PDU PAD FCS

PT DATA FCS

Octets 7 1 6 6 4 2 from 46 to 1500 4

PREAM. SFD DA SA

PREAM. SFD DA SA

IEEE 802.3

Ethernet v2.0

TAG

TAG

New Field

• Tagging Ethernet - IEEE 802.3

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Two-level tagging• The original frame is left unchanged

• A new external header is added in frontof the original frame

u New SA, DA, (RIF), Ethertype, and VLAN-IDu It is possible to support giant frames

• The RIF works better:u two-level tagging is a tunnelling mechanismu it is unclear how source routing works in 1Q

• A Tricky FCS fix-up in the new headerwould allow original frame FCS to beretained

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Inter-Switch Link (ISL)• Original frame is encapsulated with

ISL header and FCS, i.e. two leveltagging

• Support up to 1,024 VLANs

• Implemented in ASICs provideswire speed performance

ISL Header26 bytes

Encapsulated frame 1 ... 24.5 KBytesFCS

4 bytes

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ISL Header Format

DA Type

01-00-0c-00-00

User SA LEN AAAA03 HSA VLAN BPDU INDEX RES

• The higher 40 bit - multicast destination address

• Lowest 8 bits used by type and user field

Destination MACaddress

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Spanning Tree• Three different possibilities:

u Single spanning treeu Per VLAN spanning treeu Shared spanning tree

• Single spanning tree does not allow:u multiple active topologiesu load balancing

• Cisco implements one spanning treeper VLAN, at present

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Multiple Spanning Trees

Red ST

Green ST

S1

S3S2

• All links in the network aresimultaneously used

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What is a VLAN?• Two possible models

u Access VLANsn VLANs are a clever way to specify filters to

limit endstation-to-endstation connectivityon a single, bridged LAN

u Independent VLANsn VLANs are a clever way to utilize one

physical plant to carry multiple,independent bridged LANs

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Access VLANs• It is a single bridged LAN, with filters

u filtering helps in scaling somewhat larger

• Access VLANs require a singlespanning tree for the whole network,because they have one filteringdatabase for all VLANs in each bridge

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Access VLANs• One-way VLANs

u Half-duplex conversations between differentVLANs

u Bridge 1 never sees F’s source on yellow orblue, nor X’s or Y’s sources on green

u Filtering database must ignore “color”

FF XX

YY2211

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Independent VLANs• It is possible to build large networks

u if the scope of each VLAN is not globalu routers plus bridged LANs are known to scale

well

• Per VLAN filtering database

• They work with:u a single spanning treeu one spanning tree per VLANu multiple VLANs in each of several spanning

trees

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Independent VLANs• They support duplicate MAC addresses

u DECNet phase IV routers and two-EthernetSun workstations

u to route some protocols and bridge others

(Route IP)

Bridge NetBEUI

Y X

X YS2S1

X

Y

When R1 bridges some protocol between X and Y ondifferent VLANs, S1 and S2 see duplicate MACaddresses for Y and X.

R1

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Number of “filtering databases”• MFD/SE

u Multiple Filtering Database - Single Entryu Natural solution for independent VLANsu Compatible with multiple spanning trees

• SFD/MEu Single Filtering Database - Multiple Entryu Solution adopted in Access VLAN to try to

support duplicated MAC addressesu Requires a single spanning tree

• Duplicate MAC addresses arecommon!!!

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Internetworking between VLANs• Using routers

u classical approachu scale well

• Layer 2 shortcutsu switches create shortcuts between VLANsu limited scalability

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• VLAN

• IEEE 802 committeesu IEEE 802.1u IEEE 802.3acu standard tagging scheme

• IEEE 802.1p

• IEEE 802.1Q


Compass

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IEEE 802 LMSC• 802 LAN/MAN Standards Committee

u 802.1: Higher Layer Interfaces (*)n 802.1D (transparent bridging)n 802.1G (metro transparent bridging)n 802.1H (translation bridging)n 802.1D Reaffirmationn 802.1p Priorities/GARP/GMRPn 802.1Q VLANs/GVRP

u 802.3: CSMA/CD (Ethernet)n 802.3ac

u 802.5: Token Ringu Others

(*) IEEE 802.1 started working on VLANs inlate 1995 and it has still not finished

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IEEE 802.3ac• IEEE Standards for Local and

Metropolitan Area Networks:u Supplement to Carrier Sense Multiple Access

with Collision Detection (CSMA/CD) AccessMethod & Physical Layer Specification

n Frame Extension for Virtual Bridged LocalArea Networks (VLAN) Tagging on 802.3Networks.

• Draft 1

• Main topic:u Extend Maximum Frame size from 1518 to

1522 octets

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Tagging scheme

Destination Address

Source Address

EtherType = TPID

Tag Control Information

MAC Length/Type

MAC DATA

PAD

FCS

6

6

2

2

2

42-

1500

4

Used in:n IEEE 802.3acn IEEE 802.1Qn IEEE 802.1p

userpriority

CFI

VID (VLAN ID) - 12 bits

3 1

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One-level tagging• Insert Ethertype and VLAN-ID after MAC

source (or RIF), but before originalEthertype/Length (or LLC)

• Includes T-R Encapsulation bit so thatT-R frames can be carried acrossEthernet backbones without 802.1Htranslation of data contents

• 802.1p and 802.1Q share the same tag

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802.1p/Q tags

Dest Src DataLen/Etypep/Q LabelEtype FCS

Priority VLAN-ID

Token-Ring Encapsulation Flag

VLAN-ID and T-REncaps Flag are

.1Q, not .1p

RecomputeFCS

6 6 2 2 2 4...

Dest Src FCSDataLen/Etype

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• VLAN


• IEEE 802.1pu Expedited traffic capabilitiesu Bridge architectureu GARP, GMRP

• IEEE 802.1Q


Compass

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IEEE 802.1p• IEEE Standards for Local and

Metropolitan Area Networks:u Supplement to Media Access Control (MAC)

bridges: Traffic Class Expediting and DynamicMulticast Filtering

• Draft 8

• Two main topics:u Expedited traffic capabilitiesu Filtering services to support the dynamic use

of Group MAC addresses

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Expedited traffic capabilities• Priority labeling

u MAC-layer priority in the add-on tagu Priority not derived from MAC address

• Multiple output queues per output portu output queue selection based on 802.1p tagu maintains ordering only between frames at

same priority

• 802.1 is cooperating with IETF’s ISSLL(Integrated Services over SpecificLower Layers)

u mapping L3 RSVP requests to 802.1p prioritiesvia a subnet bandwidth manager

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Bridge architecture

Source PortState Information

Destination PortState Information

FilteringDatabase

Frame reception Frame discarding Frame transmission

3.7.1 3.7.2 3.7.3 Queues 3.7.4 3.7.5 3.7.6

3.7.1 Enforcing topology restriction3.7.2 Filtering Frames3.7.3 Queueing Frames

3.7.4 Selecting frames for transmission3.7.5 Mapping priority3.7.6 Recalculating FCS

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GARP• Generic Attribute Registration Protocol

u Generic attribute dissemination capabilityu Used by participants in “GARP Applications

(*)” (GARP Participants) to Register and de-register attribute values with other GARPparticipants within a bridged LAN

u Attribute types and attribute values arespecific of each GARP application

u Designed to register anything

(*) there are two GARP Applications alreadydefined: GMRP and GVRP

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GARP operation• GARP Applications

u make/withdraw declarations relative toattribute values

u this results in registration/deregistration ofattribute values in other GARP participants

u registration/deregistration is recorded in astate variable in the “Registar state machine”

n only on the port that receives the GARPPDU containing the declaration

n even on ports that are not ST forwardingu attribute values registered on ports belonging

to the active topology are propagated to all theother bridge ports belonging to the activetopology by the “Applicant state machine”

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Declaration and Registration

Aa

a a

a a

a

a

A = Declaration of attribute value Aa = Registration of attribute value A Propagation of declaration

Switch

End Station

a

A A

A

A

a

a

a

A

A A

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From two end stations

Aaa

Aa a

a a

a

a Switcha

A A

Aa

A

Aa

Aa

Aa

Aa

Aa A

A = Declaration of attribute value Aa = Registration of attribute value A Propagation of declaration

End Station

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Active topology

Aaa

Aa a

a a

a

a Switcha

A A

Aa

A

Aa

Aa

Aa

Aa

Aa A

A = Declaration of attribute value Aa = Registration of attribute value A Propagation of declaration Active topology

End Station

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GARP Participant• In each bridge it consists of a GARP

application and a GID per each port

• GID (GARP Information Distribution)u a set of state machines that defines the

current registration and declaration state of allattribute values

• GIP (GARP Information Propagation)u propagation of information between GARP

participantsu within a bridgeu between bridges

n based on LLC Type 1 service

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GARP architecture

GARPapplication

GID

GARP participant

LLC

FrameRX

FrameTX

MACrelayentity

GARPapplication

GID

GARP participant

LLC

FrameRX

FrameTX

GARPapplication

GID

GARP participant

LLC

FrameRX

FrameTX

End Station

Bridge

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GID architecture

ApplicantState

Machine

RegistarState

Machine

Attribute n state:

ApplicantState

Machine

RegistarState

Machine

Attribute n-1 state:

ApplicantState

Machine

RegistarState

Machine

Attribute ... state:

ApplicantState

Machine

RegistarState

Machine

Attribute ... state:

ApplicantState

Machine

RegistarState

Machine

Attribute C state:

ApplicantState

Machine

RegistarState

Machine

Attribute B state:

ApplicantState

Machine

RegistarState

Machine

Attribute A state:

GID

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GMRP(GARP Multicast Registration Protocol)

• Multicast group membership at MAClayer (MAC layer version of IGMP)

u Allows endstations to register for the MACmulticasts that they want

u Tracks which ports request each multicastaddress

u Allows frame switches to send multicasts onlywhere they’re needed

u Allows endstations to register for all MACmulticasts

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GMRP• GMRP attributes

u Group Membership Informationn Composition of the groupn The attribute type is the 48-bit multicast MAC

addressn Updating Filtering database to indicate the

ports on which members of the groups havebeen registered

u Default Group behavior:n Filter Unregistered Groups (default)n Forward All Groupn Forward Unregistered Group

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GMRP

Application station belonging to Group M

Group Registration entry for Group M

Application station NOT belonging to Group M

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Priority tagged frame• The 1Q/1p tag can be used also in

absence of VLANs

• Useful to carry priorities

• It is sufficient to set the VID = 0u The receiving port will retag the frame using

the PVID (Port VLAN ID)

Switch VID=0, Prio=5

PVID=4

Incoming frameThe received frame is retagged with VID = 4

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• VLAN


• IEEE 802.1p

• IEEE 802.1Qu architectural modelu GVRPu relaying functionu port-based VLANs - native VLANu spanning tree issuesu interaction between 1Q and 1p


Compass

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IEEE 802.1Q• IEEE Standards for Local and

Metropolitan Area Networks:u Virtual Bridged Local Area Network

• Draft 7

• Two main topics:u Bridged/switched networksu VLANs (Virtual LANs)

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IEEE 802.1Q• Defines the capabilities of a “VLAN-

aware” bridge

• Adds to IEEE 802.1D the VLAN supportu it interoperates with “VLAN-unaware” bridges

• Compared to proprietary solutions:u it is lateu it has a limited set of features

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Architectural choices• Per-port VLANs only

u Assigning frames to VLANs by filtering, e.g.using L3 information, is allowed but notspecified in the standard

• Single spanning tree

• Explicit taggingu one level tagging

• Supports both SFD/ME and MFD/SE

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Architectural model

Relay

Distribution ofconfiguration Information

Configuration

Registration

protocols

Ingress

rules

MIBs

Topology distribu-

tion protocols

Forwarding

rules

Egress

rules

Management

GVRP

SpanningTree

Classifying a frame as belonging to a VLAN

Forwarding or filtering the frame

Output portstagged/untagged

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802.1Q VLANs• VLANs based on three-layer approach

u Configuration: netadmin sets parametersu Distribution: switches agree on working

details (to minimize configurationrequirements)

u Relay: frames are assigned to VLANs anddistributed

• The distribution protocol is GVRPu it tells which switches want which VLANs

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Relaying function

ForwardingProcess

IngressRules

EgressRules

FrameTransmission

Port StateInformation

Port StateInformation

FrameReception

Filteringdatabase

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GVRP(GARP VLAN Registration Protocol)

• VLAN membershipu End stations and bridges may issue or revoke

declarations relating to the membership ofVLANs

u The attribute type is the 12 bits VID (VLAN ID)

• Service primitivesu ES_REGISTER_VLAN_MEMBER(VID)u ES_DEREGISTER_VLAN_MEMBER(VID)

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Port-based VLANs

VLAN A

VLAN B

accessport

VLAN-awarebridge trunk

link

VLAN A

VLAN B

accessport

VLAN-awarebridge

• Does not support user mobility nordecision based on higher levelinformation

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Native VLAN• Each physical port has a PVID (Port

VLAN-ID) to which all untagged framesare assigned

VLAN A

VLAN B

accessports

VLAN-awarebridge

trunklink

accessports

VLAN-awarebridge

VLAN-awareend station

VLAN B

VLAN-unawareend station


VLAN A

VLAN B

VLAN C


PVID=C

PVID=A

PVID=B

VLAN C

PVID=C

PVID=C

PVID=C

accessport

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A spanning tree problem• Mixing VLAN-aware and VLAN-unaware

switches

n If the port X is blocked the network works finen If the port Y blocks VLAN A is partitioned (the

server A is unreachable from VLAN A)

SWITCHVLAN-aware

bridge 802.1DVLAN -unaware

VLAN A

Server B(VLAN B)

VLAN B

Server A(VLAN A)

X

Y

bridge 802.1DVLAN -unaware

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A worse spanning tree problem

SWITCHVLAN-aware

SWITCHVLAN-aware

accessports

VLAN A

VLAN B

• The single spanning tree will block oneof the two VLANs

• This situation is normal andunavoidable in the case of two VLANsimplemented with ATM/LANE

Blocked

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Interaction between 1Q and 1p• 1p introduces GARP

u 1p specifies how to forward frames in amulticast environment using GMRP

• 1Q introduces GVRP and specifies howto forward frames in a VLANenvironment

u on which portsu on which VLANsu tagged or native format

• 1p specifies how to encode the framepriority

an engineering guide to ieee 802.1q and ieee...

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