More on SPB-V
Shortest Path Bridging V-mode
Norman Finn
Ver. 01
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IEEE 802.1 interim meeting, York, UK, May, 2012
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Overview
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IEEE 802.1 interim meeting, York, UK, May, 2012
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Spanning Tree
A(0)
B
C
D
E
F
A(0)
A
A advertises “I am the root.”
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IEEE 802.1 interim meeting, York, UK, May, 2012
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Spanning Tree
A(0)
A(1)
B
D
E
C
A(0)
A(1)
A
F
A(1)
A advertises “I am the root.”
B and D advertise “I am one hop from the root.”
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IEEE 802.1 interim meeting, York, UK, May, 2012
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Spanning Tree
A(0)
A(1)
B
D
E
C
A(0)
A(1)
A
A(1)
F
A(2)
A advertises “I am the root.”
B and D advertise “I am one hop from the root.”
E advertises “I am two hops from the root.”
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IEEE 802.1 interim meeting, York, UK, May, 2012
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Spanning Tree
A(0)
A(1)
B
D
E
C
A(0)
A(1)
A
A(1)
F
A(2)
A advertises “I am the root.”
B and D advertise “I am one hop from the root.”
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.”
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IEEE 802.1 interim meeting, York, UK, May, 2012
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IS-IS
A:B,D
A:B,D
A
B
C
D
E
F
A advertises, “I am A. I connect to B and D.”
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IEEE 802.1 interim meeting, York, UK, May, 2012
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IS-IS
B:ACE
A
B:ACE
D
B:ACE
B
C
E
F
A advertises, “I am A. I connect to B and D.”
B advertises, “I am B. I connect to A, C and E.”
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IEEE 802.1 interim meeting, York, UK, May, 2012
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IS-IS
B:ACE, B:ACE,
A:BD
A:BD
A
B
C
B:ACE
A:BD
D
E
F
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.”
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IEEE 802.1 interim meeting, York, UK, May, 2012
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IS-IS
A:BD
B:ACE
C:B
D:AE
E:BDF
F:E
A
B
C
D
E
F
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.)
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IEEE 802.1 interim meeting, York, UK, May, 2012
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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”).
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IEEE 802.1 interim meeting, York, UK, May, 2012
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Frame formats for bridging schemes
MSTP
Dest. Src.
Qtag*
Data CRC
SPB-V
Dest. Src.
Qtag*
Data CRC
Dest. Src.
Ctag
Data CRC
Dest. Src.
Ctag
Data CRC
SPB-M
(MAC-in-MAC)
TRILL
last B
first B
Btag
Itag
next B prev B Qtag TRILL
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.
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IEEE 802.1 interim meeting, York, UK, May, 2012
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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.
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IEEE 802.1 interim meeting, York, UK, May, 2012
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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-inMAC.
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IEEE 802.1 interim meeting, York, UK, May, 2012
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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.
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IEEE 802.1 interim meeting, York, UK, May, 2012
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MSTP/SPB-V data plane difference
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IEEE 802.1 interim meeting, York, UK, May, 2012
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SPB-V unicast ignores bridge ID
source
q sends a frame to x
p
C
A
Each bridge ( B )
is a spanning tree
root. Tree B is
blocked at
B
D
B
q
E
VID = E + VLAN
B
VID = C + VLAN
E
C
sink
source
x
D
A
y
sink
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.
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IEEE 802.1 interim meeting, York, UK, May, 2012
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SPB-V multicast uses bridge ID
source
p and q are both sources
for multicast group G
p
C
A
D
q
x and y are both
sinks for
multicast group G
sink
x
E
VID =
A + VLAN
B
source
B
VID = E + VLAN
E
C
D
A
y
sink
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.)
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IEEE 802.1 interim meeting, York, UK, May, 2012
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MAC address lookups: MSTP
unicast frame
VLAN ID
unicast
source
map
FDB
ID
multicast frame
unicast
dest.
map
unicast
source
Source
lookup
FDB
ID
VLAN ID
map
unicast
dest.
Destination
lookup
FDB
ID
unicast
source
multicast
dest.
map
unicast
source
Source
lookup
FDB
ID
multicast
dest.
Destination
lookup
Multicast lookup is same as unicast lookup.
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IEEE 802.1 interim meeting, York, UK, May, 2012
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MAC address lookups: SPB-V
unicast frame
VLAN ID
unicast
source
map
FDB
ID
multicast frame
unicast
dest.
map
unicast
source
Source
lookup
FDB
ID
VLAN ID
Destination
lookup
FDB
ID
multicast
dest.
no
map
map
unicast
dest.
unicast
source
unicast
source
Source
lookup
VLAN ID
multicast
dest.
Destination
lookup
Multicast lookup is different than unicast lookup.
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IEEE 802.1 interim meeting, York, UK, May, 2012
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The Filtering Database: MSTP
FDB ID (FID)
MAC address
Port(s)
One entry per VLAN
for unicasts
VLAN = 5
00:00:0c:00:00:01
3
VLAN = 5
00:00:0c:00:00:02
15
One entry per VLAN
for multicasts
VLAN = 5
01:00:0c:00:22:00
3, 7, 16
VLAN = 5
01:00:0c:00:99:00
12, 31
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IEEE 802.1 interim meeting, York, UK, May, 2012
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The Filtering Database: SPB-V
One entry per VLAN
for unicasts
One entry per VLAN
per Bridge for
multicasts
new-AVB-nfinn-more-spb-v-0412-v01.ppt
FDB ID (FID)
MAC address
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
IEEE 802.1 interim meeting, York, UK, May, 2012
Port(s)
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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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IEEE 802.1 interim meeting, York, UK, May, 2012
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