Transcript new-enni-nbragg-Light-ENNI-0810-v01.ppt

Light ENNI – aka Split LAG …
a
a
Region C
3
b
b
Region A
Link
Aggregation
c
Basic Forwarding Rules :
 a frame from the network is loaded into a locally-attached LAG link :
 if the whole LAG on that node fails, it blocks its “Region-facing” ports
 on egress from a LAG, a frame may have to pass over an IST (==) to
ensure that it enters the destination region via the correct port :
 only one port can be open to any destination, otherwise frame looping
and duplication start, and MAC learning breaks;
 MAC learning is also shared and synchronised over the IST
 ISTs must be proof against single point of failure :-“split brain” issue :
 modulo Norm’s “suicide pact” suggestion;
 they can also be built as LAGs in their own right if desired
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
Light ENNI – aka Split LAG …
a
a
Region C
3
b
b
LAG
Region A
Link
Aggregation
c
The easiest way to access this structure is “triangular” Split LAG :
 exactly one frame is sent in, and exactly one frame comes out

But this looks very “heavy” for a light ENNI 

The alternative is to make {a, b, c …} full participants in their region’s
control regimes :
 which if this is xSTP looks “interesting”; next slide
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Light ENNI – aka Split LAG …
a
a
Region C
3
b
b
Region A
Link
Aggregation
c
The alternative is to make {a, b, c …} full participants in their region’s CP :
 xSTP is the challenging case
There can only be a single unblocked point of attachment of the virtual
bridge (3a, 3b, 3c ) to the region’s Spanning Tree on any VLAN :
 the structure above duplicates frames on flooding ,
 and “thrashes” source learning for frames travelling 
The Spanning Tree root cannot be placed “on” a virtual bridge element :
 the Region may have > 1 E-NNI
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Light ENNI – aka Split LAG …
a
a
PN
b
Region C
3
b
Region A
Link
Aggregation
c
In a Link State environment, the solution is straightforward :
 all bridges in Region C can obtain a common view of which of
{a, b, c} is on the shortest path to a “PN”, and act accordingly
When running xSTP, the ENNI probably has to do this “by the back door” :
 the xSTP on {a, b, c} has to be extended to allow “private” sharing of
Root Path Priority Vector between a  b, a  c, and b  c :
 with the winner being the owner of the unblocked port;
 unless there is a better idea … ?
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“One we made earlier”
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SPBM for resilient PB E-NNI
I-SID = z
S-Tag = y
PB
NW 1
SPBM
PB
NW 2
S-Tag = x
I-SID = z
Operators 1 & 2 bind each PB S-tag to a common SPBM I-SID
Each operator is responsible for advertising that I-SID once only
into the SPBM domain :
 but each operator has complete authority as to where that is
So long as a viable path remains available in the SPBM domain,
connectivity will automatically be maintained by SPBM.
I-SiDs are provisioned in SPBM :
 a signalled interface might be desirable
 MVRP ?
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