IEEE 802 LMSC Resilient Packet Ring Study Group Status Report Mike Takefman Chair of RPRSG www.ieee802.org/rprsg [e-mail]

1
PIRC Architecture July 2007 Plenary Session San
Francisco Mike Takefman Cisco Systems
2
My PIRC High Level Goals

• Built on top of 802.17b MAC
• Assumption is an L2 switched network
• PIRC has to provide loop-free dual connectivity
• Multiple Load-Balancing methods
• Compatible with non-PIRC stations
• ideally no MAC or operational changes needed for
  other nodes
• usable with existing standard product chips

3
Where To Put Filtering

• PIRC is essentially adding new filtering rules to
  the system
• assumption is that ingress and egress filter
  rules exist
• Our scope requires that these filtering rules
  exist in the MAC level, but the actual position
  is implementation dependant
• side effect on whether 802.17b learning occurs
• no easy way to arbitrarily allow or not allow
  learning
• question is one of compliance
• Tributary support requires egress filtering rules
  in addition to ingress rules

4
Hash Filtering

• Previous presentations have pointed out that
  certain constraints must be followed in order to
  insure connectivity
• net result is that the basic hash function is
  based on outer VLAN
• hence this form of hash filtering is essentially
  VLAN filtering and any other hashing function is
  by definition proprietary

5
2 Span Failure Scenarios

• It has been suggested that PIRC support both 1
  and 2 span failures
• it must be assumed that the network is otherwise
  loop free
• 2 cuts on a leaf ring is trivial as a loop cannot
  be created
• 2 cuts on an intermediate ring is more
  interesting and has a few cases

D
C
B
A
6
2 Span Failure Scenarios

• Isolated Node
• no connectivity to that node
• no loops created
• Nothing can be done, and there are no PIRC issues

D
C
B
A
7
2 Span Failure Scenarios

• Isolated Neighbour Ring
• no connectivity to that sub-tree
• no loop created
• Nothing can be done, and there are no PIRC issues

D
C
B
A
8
2 Span Failure Scenarios

• Isolated Partial Ring
• full connectivity possible
• no loop created
• PIRC could restore connectivity
• AB operated normally
• DC both do full forwarding

D
C
B
A
9
2 Span Failure Scenarios

• Split Ring
• full connectivity possible BUT
• loop created with current suggested PIRC
  filtering
• PIRC could restore connectivity
• AB, CD forward everything from neighbour ring
  to broken ring
• one of AB, CD forward to neighbour ring
• never forward back from mate
• done with egress filtering if tribs are needed
  else ingress

D
C
B
A
10
2 Span Failure Scenarios

• How to recognize split ring? Nodes on affected
  ring observe
• mate has disappeared on one ring but not the
  other

D
C
B
A
11
2 Span Failure Scenarios

• Does the split ring scenario scale to 3 PIRC
  pairs?
• AB,CD are partially isolated from BE
• AB is split from CD
• the problem is that the split rules are
  different from the partially isolated rules
• implies you need to apply rules based on ringSA
  -gt YUCK

D
C
B
E
F
A
12
Conclusions

• Dual Failure scenario can only be handled for
  limited cases
• likely not worth doing