Ethernet Bridging Gestione del traffico su reti Metro Ethternet.

Ethernet Bridging

Gestione del traffico su reti Metro Ethternet

Sommario

Riepilogo Carrier EthernetRiepilogo Spanning Tree ProtocolProblemi con STP in reti MANSoluzioni proposte: SPB

Calcolo dei pathForwarding

Altra soluzione :TRILL

Perché ethernet nelle MAN?!

<10 €

Broadcast on unknown = tecnologia plug-and-play

Riassunto: Metro Ethernet I

Riassunto: Metro Ethernet II

IEEE 802.1d

IEEE 802.1 ah

Gestione

Continuity Check messages = "heart beat" messages. Detect connectivity failures in an MA. CCMs are multicast messages and they are confined to a domainLink Trace messages = track the path (hop-by-hop)Directly to the Originating MEP, and regenerates the Trace route MessageLoop-back messages = determine the location of a faultAdministratively initiated and stoppedITU-T Y.1731 additionally supports the following:

Loss MeasurementOne way DelayTwo way Delay

Sommario




Spanning Tree ProtocolÈ necessaria una topologia fisica ridondante (supporto fault), ma è necessario che quella attiva sia loop-free (broadcast on unknown)Soluzione: disattivazione di alcuni linkScelgo la root in maniera casuale (ID più basso) ed ogni bridge si calcola il percorso più breve per raggiungerla.

IEEE 802.1 D

Sommario




Problemi con STP in reti MAN

In caso di fault devo ricostruire le forwarding table, quindi molti broadcastNon utilizzo percorso ottimoNon utilizzo tutta la banda che ho messo in campoAnche con RSTP (IEEE 802.1W) tempo di convergenza troppo altoNon posso gestire in maniera semplice il traffico

Perché ho bisogno di gestire il traffico?

AffidabilitàControllo della banda per servizioRispetto Service Level Agreement (SLA)

PBB-TE traffic engineering

Sommario




SPB shortest path bridging

IEEE 802.1 ad (SPBM in ambito PBB)Calcolo di più path all’interno della reteShortest path bridging MAC operation uses MAC addresses to identify the SPT24 bits of the 802.1ah header service instance (I-SID) provide highly scalable support for service virtualization

SPB conceptSPT Region

SPVID = 45

SPVID = 41VID = 6

DASA

Payload

45

DASA

Payload

22

DASA

Payload

41

DASA

Payload

22

DASA

Payload

22

CSTIST

DASA

Payload

45

DASA

Payload

41

SPVID = 71

SPVID = 66SPVID = 44

SPVID = 22

DASA

Payload

22

Base VID 22

SPB operation

IS-IS IS-IS IS-IS

IS-ISIS-IS

IS-IS

BEB

BEBBEB

BCB BCBBEB “A”

BEB Backbone Edge Bridge BEB

PBBN

IS-IS

IS-IS IS-IS

Backbone Core Bridge BCB

Shortest path between any two points is both the same and symmetrical for unicast and

multicast

SPB path da/per A

IS-IS IS-IS IS-IS

IS-ISIS-IS

IS-IS

BEB

BEBBEB

BCB BCBBEB “A”


PBBN

IS-IS

IS-IS IS-IS


Shortest path between any two points is both the same and symmetrical for unicast and

multicast

All pairs shortest path computation performed in

parallel

SPBB Multicast Groups

IS-IS IS-IS IS-IS

IS-ISIS-IS

IS-IS

BEB

BEBBEB

BCB BCBBEB “A”


PBBN

IS-IS

IS-IS IS-IS


I-SID 5

I-SID 5I-SID 5

MMAC for 5 from A

I-SIDs define efficient subsets

Sommario




Soluzione iniziale: MSTP

Network loop prevention requires synchronizing state at island/core boundaries with bridges that only understand RSTP/MSTP BPDUsThat means:

using ISIS-SPB results in BPDUsinjecting BPDU information into ISIS-SPB

ISIS-SPB can make some decisions faster, e.g. determine CIST Port Roles and priority vectors

Stop existing mechanisms from overriding with temporarily incorrect information

Ports inside SPT Regions synchronize forwarding state with boundary ports

Need to specify how, without reinvention

Have to interoperate with existing bridges, and deploy in islands/network cores

Perché è stato scelto IS-IS?

Perché è stato scelto IS-IS?

IS-IS

IS-IS is the Intermediate System to Intermediate System intra-domain routing protocolUsato per il calcolo dei path all’interno della reteDisegnato originariamente per OSI routingFacilmente estensibile

Punti di contatto IS-IS e OSPF

Link state protocolsHello packets per trovare e mantenere le adiacenzeDijkstra / SPF algorithmVisione gerarchica della topologia della reteCosto è metrica di default

Per questo IS-IS può essere usato su Ethernet: estendo le funzionalità aggiungendo TLVs per portare informazioni riguardanti le VLAN, la

mappatura VID, gli indirizzi multicast, gli identificativi CIST, la service

group membership…

Differenze tra IS-IS e OSPF

ISIS Link State Packets contengono TLVs, mentre OSPF Link State Updates contengono Link State Advertisements (LSAs)

ISIS -SPB

Uses the standard ISIS procedures to construct and update the link state database in each SPT bridgeDisable B-MAC learning inside the backbone, only “border” learningSets up and maintains at least one SPT for each bridge, which connects to every other bridge in an SPT regionSupport multiple path with same cost

ISIS -SPB

SPTs have to meet two congruency criteria.Forward and reverse paths must be the same between any two bridge pairsUnicast and multicast paths also have to be congruent

ISIS -SPB

Can raise temporary loopLoop mitigation: ingress filteringLoop avoidance: discard until neighbor topology match

Sommario




SPB Computation – Classic Method

For every node in the network do:Compute SPT: run Dijkstra for the node (the root of the spanning tree)Prune paths: keep only the shortest paths that go through the node performing the computationI-SID computation: compute the intersection of the set of I-SIDs for which the root node transmits with the set of I-SIDs for which the paths’ endpoints receivePluses:

Simple, elegant, and quite efficient when most paths are not prunedBest possible worst-case performance

Minuses:

Most of the paths computed by some nodes, most notably edge nodes, end up being pruned (because they are not offering transit)For these nodes, the SPB computation can be very expensive relative to the amount of forwarding state produced


Unicast

DA-MAC

DA-BMAC

PATHID

S-VID ISID

Paths list

Multipathing


Multicast

DA-MAC

DA-BMAC

PATHID

S-VID ISID

Paths list

Multipathing

TRILL

Transparent Interconnection of Lots of LinksSimile all’SPB, ma

Standardizzato da IETFOttimizzato per ambiente Data CenterNon compatibile con architettura reti PBBGestione dei loop temporanei con TTL

TRILL

Gestione e troubleshooting più complicati

Sara LagoIPI Lab

[email protected]

Ethernet Bridging Gestione del traffico su reti Metro Ethternet.

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