More on SPB-V

1IEEE 802.1 interim meeting, York, UK, May, 2012new-AVB-nfinn-more-spb-v-0412-v01.ppt

More on SPB-V

Shortest Path Bridging V-modeNorman FinnVer. 01


Overview


Spanning Tree

A advertises “I am the root.”

A

D

B

E

C

F

A(0)

A(0)


Spanning Tree


B and D advertise “I am one hop from the root.”

D

B

E

C

F

A(0)

A(0)

A(1)

A(1)

A(1)

A


Spanning Tree



E advertises “I am two hops from the root.”

D

B

E

C

F

A(0)

A(0)

A(1)

A(1)

A(1)

A(2)

A


Spanning Tree



E advertises “I am two hops from the root.”

F knows nothing of the path to A; only the distance. Each bridge modifies the data along the way. That is “global information distributed locally.”

D

B

E

C

F

A(0)

A(0)

A(1)

A(1)

A(1)

A(2)

A


IS-IS

A advertises, “I am A. I connect to B and D.”

A

D

B

E

C

F

A:B,D

A:B

,D


IS-IS

A advertises, “I am A. I connect to B and D.”

B advertises, “I am B. I connect to A, C and E.”

A

D

B

E

C

F

B:ACE B:ACE

B:A

CE


IS-IS

Furthermore, as soon as B hears A’s advertisement, it relays A’s information to its neighbors.

That is, B says, “I am B. I connect to A, C, and E. A says that it connects to B and D.”

A

D

B

E

C

F

B:ACE,A:BD

B:ACE,A:BD

B:A

CE

A:B

D


IS-IS

Eventually, every switch in the network has the state of every other switch, and relays all bridges’ data to its neighbors verbatim. That is “local information distributed globally.”

(Of course, there are tricks so that a huge volume of information is not constantly retransmitted.)

A

D

B

E

C

F

A:BDB:ACEC:BD:AEE:BDFF:E


Shortest Path Bridging – V-mode

802.1aq SPB-V control plane is IS-IS

o Standard IS-IS, SPB-V code points granted from IETF. Can mix bridging and routing TLVs in one packet.

Data frames use Q-tag; no extra header, no MAC-in-MAC.

o Q-tag encodes both source bridge ID (multicast tree ID) and VLAN (community of interest) in the VLAN ID.

Data plane is almost identical to classical bridge data plane.

Uses control-plane interlocks to prevent loops, not TTL to mitigate them (but avoids MSTP brain-death issue).

Data plane learns source MAC addresses (and flushes learned addresses when necessary), but this need not prevent distributing MAC addresses in IS-IS (“host routing”).


Frame formats for bridging schemes

Q-tag in MSTP codes 4094 VLANs

Q-tag in SPB-V codes (VLAN) • (Bridge ID) < 4095, e.g. 4 VLANs and 1023 bridges, or 15 VLANs and 256 bridges.

Dest. Src. Qtag* Data CRC

Dest. Src. Qtag* Data CRC

Dest. Src. Ctag Data CRC

Dest. Src. Ctag Data CRCnext B prev B Qtag TRILL

last B first B Btag Itag

MSTP

SPB-V

SPB-M(MAC-in-MAC)

TRILL


SPB-V vs. Multiple Spanning Tree Prot. Every frame, unicast or multicast, takes the least-cost path. SPB-V is compatible with MSTP in that:

o SPB-V can control some VLANs, while MSTP runs simultaneously, controlling other VLANs (and other protocols control other VLANs).

o SPB-V interfaces seamlessly with MSTP at cloud boundaries.o Only VLAN translation (no encapsulation) at MSTP/SPB-V

boundaries.

SPB-V, based on IS-IS, has much faster worst-case convergence time.o Loop-prevention interlocks are faster than MSTP interlocks in the

worst case, because they are link-state based.

SPB-V can replace protocols (e.g. VLAN pruning) that run after MSTP convergence with link state advertisements requiring only recomputation after a topology change.

SPB-V limits the number of VLANs available.


SPB-V vs. SPB-M with MAC-in-MAC

SPB-V uses only the usual VLAN tag. 802.1aq SPB-M + MAC-in-MAC encapsulates the customer frame.

SPB-V core bridges use customer addresses == the only addresses in the frame, so SPB-M is better for large networks.

SPB-V limits the number of VLANs available.

Given an MSTP data plane, support for an SPB-V data plane is a small change, compared to MAC-in-MAC.


SPB-V vs. SPB-M without MAC-in-MAC

SPB-V uses only the usual VLAN tag. 802.1aq SPB-M adds an I-tag (VLAN-tag is optional).

SPB-V limits the number of VLANs available. SPB-M supports 16M VLANs, somewhat more than the typical home requires.

SPB-V supports the existing multicast MAC addresses used by all of the protocols developed over the past 30 years.

SPB-M without MAC-in-MAC supports only engineered multicast MAC addresses, does not support existing multicast MAC addresses, and thus requires changes to most existing end stations’ software.


MSTP/SPB-V data plane difference


SPB-V unicast ignores bridge ID

E floods qx frame because address x is unknown.

C learns address q without Bridge ID E, because it will transmit to q using its own Bridge ID C.

D learns both addresses without Bridge ID.

C D

B E

A

A

B

C

D

E

psource

q source

xsink y sink

q sends a frame to x

VID = E + VLAN

VID = C + VLAN

Each bridge ( )is a spanning treeroot. Tree B isblocked at

B

B


SPB-V multicast uses bridge ID

To reach C, D must pass frames from E.

To avoid duplication, D must not pass frames from A.

(C is reached from A via B.)

C D

B E

A

A

B

C

D

E

psource

q source

xsink y sink

p and q are both sourcesfor multicast group G

x and y are bothsinks formulticast group G

VID =A + VLAN

VID = E + VLAN


MAC address lookups: MSTP

Multicast lookup is same as unicast lookup.

unicast source

unicast dest.

unicast source

multicast dest.

map map map

Sourcelookup

Sourcelookup

Destinationlookup

Destinationlookup

map

FDB ID

FDB ID

FDB ID

FDB ID

unicast source

unicast dest.

unicast source

multicast dest.

VLAN ID VLAN ID

unicast frame multicast frame


MAC address lookups: SPB-V

Multicast lookup is different than unicast lookup.

unicast source

unicast dest.

unicast source

multicast dest.

map map mapno

map

Sourcelookup

Sourcelookup

Destinationlookup

Destinationlookup

unicast frame multicast frame

FDB ID

FDB ID

FDB ID

VLAN ID

unicast source

unicast dest.

unicast source

multicast dest.

VLAN ID VLAN ID


The Filtering Database: MSTP

FDB ID (FID) MAC address Port(s)

VLAN = 5 00:00:0c:00:00:01 3

VLAN = 5 00:00:0c:00:00:02 15

VLAN = 5 01:00:0c:00:22:00 3, 7, 16

VLAN = 5 01:00:0c:00:99:00 12, 31

One entry per VLANfor unicasts

One entry per VLANfor multicasts


The Filtering Database: SPB-V

FDB ID (FID) MAC address Port(s)

BID = 0 VLAN = 5 00:00:0c:00:00:01 3

BID = 0 VLAN = 5 00:00:0c:00:00:02 15

BID = 3 VLAN = 5 01:00:0c:00:22:00 3, 7, 16

BID = 4 VLAN = 5 01:00:0c:00:22:00 3, 12, 16

BID = 7 VLAN = 5 01:00:0c:00:22:00 6, 16

BID = 3 VLAN = 5 01:00:0c:00:99:00 12, 31

BID = 4 VLAN = 5 01:00:0c:00:99:00 31

BID = 7 VLAN = 5 01:00:0c:00:99:00 12, 31

One entry per VLANfor unicasts

One entry per VLANper Bridge formulticasts


Additional multicast FDB entries

The additional entries are the inevitable price for optimal forwarding.

One can trade off table size vs. pruning accuracy.

For Reserved Streams, one need only install multicast entries for specific source Bridges, not for all bridges.

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