TRILL Working Group

1
TRILL Working Group

• draft-gai-perlman-trill-encap-00.txtas modified
  by Radia
• Ed Bowen, IBM
• Dinesh Dutt, Cisco
• Silvano Gai, Nuova
• Radia Perlman, Sun

2
Proposed Shim Header
9 1 6
Reserved M Hop Limit
Egress Rbridge Address
Ingress Rbridge Address
32 bits
3
Encapsulation over Ethernet
4
Hop Limit

• 6-bit unsigned integer.
• This is decremented by 1 at each node that
  forwards the frame. The frame is discarded if Hop
  Limit is decremented to zero.
• Need to define what happens on the egress RBridge
• This field was previously referred to as TTL
  (Time To Live). In IPv6 the IETF has replaced the
  concept of TTL with Hop Limit.

5
Ingress/Egress Rbridge Addresses

• Both required for
• Conventional protocol design
• more future proof
• IEEE 802.1au BCN in the CRED
• Extended ACLs
• Similar to an RPF check
• Policy-based forwarding
• Troubleshooting, debugging, and tracing
• Learning
• Encoding other information for multicast

6
How many bits for addresses

• 16 bits
• I.e. 64K RBridges
• Forecast for largest layer 2 networks
• 100,000 stations, 800 switches
• 64K gives us a safety factor of 80
• Even assuming that all switches will be replaced
  by RBridges

7
M bit

• M 0
• The frame is a unicast
• The egress RBridge address contains the egress
  RBridge ID
• M 1
• The frame is a broadcast/multicast
• The egress RBridge address contains the Tree
  ID

8
Motivation for specifying the tree

• TRILL supports multipathing for unicast.
• For multicast TRILL currently uses IRT
• all multicast traffic from an ingress RBridge
  uses the same links, i.e. no multipathing.
• By specifying the tree
• Adds multipathing and load balancing support
• Allows the ingress RBridge to select among a
  number of trees.

9
Trees

• The Ingress RBridge
• Can choose any tree as a local decision
• Its decision is recorded in the egress RBridge
  address
• The core RBridges
• Forward the frame according to the recorded value
• No tree jumping
• No consistent hashing required in core

10
Limits on Djikstra computation

• For unicast each RBridge computes one Djikstra
  instance
• independent of the number of RBridges
• IRT adds as many Djikstra computations as the
  number of RBridges
• Not a scalable solution in large networks
• Not scalable for more than hundreds of trees

11
Lets reduce the of Trees

• Lets define few trees that are used by all
  RBridges
• number of Djikstra computations equal to number
  of trees used
• N trees rooted in N RBridge
• Configuration can specify
• N (less than or equal to of RBridges)
• Rbridge Root Priorities

12
Other Open issues

• Broadcast storm prevention
• Optimization for point-to-point links
• Wiring Closet solution
• LIDs

13
Conclusions

• These slides replacedraft-gai-perlman-trill-enca
  p-00.txt
• Ingress/Egress Rbridge addresses
• Trees
• Load balancing for multicast
• Reduced number of trees
• Open issues
• Need to be addressed