Shortest Path First; Multiple Equal-Cost Paths; Examples Of One-Hop Paths - EMC Connectrix EC-1200 Planning Manual

Fibre Channel Switching Concepts
2

Shortest Path First

Multiple Equal-Cost
Paths
2-22
Connectrix v6.02 Planning Guide
In Figure 2-6, every source is only one hop away from its destination.
If frames from an N_Port on Domain ID 1 are destined for an N_Port
on Domain ID 3, the director routes these frames over one of the
diagonal ISLs between those two directors. All frames entering the
fabric from this N_Port will use this ISL to get to Domain ID 3.
Server
with
PowerPath
HBA
HBA

Examples of One-Hop Paths

Figure 2-6
Background: One N_Port initiates a frame transmission to another N_Port.
Every frame has a Destination ID (DID) in its header. The DID is a 24-bit
value with the upper 8 bits determining the destination domain and the
middle 8 bits determining the destination port. The fabric uses this DID to
route the frame domain to domain and then to its final port.
When there are multiple equal-cost paths between a source and a
destination, the routing algorithm spreads the load over the multiple
paths in a round robin fashion, sequentially assigning a set of entry
ports to a set of exit ports so that each exit port has the same number
of assigned entry ports (or a difference of only one).
Round robin port assignment ensures that a pair of ISLs will not end
up with a set of no-load ISL entry ports (as in the case of a full mesh
with no more than one hop) on one port and a set of busy N_Ports on
the other ISL.
Connectrix Connectrix
Domain ID 1 Domain ID 2
Connectrix Connectrix
Domain ID 4 Domain ID 3
Symmetrix
Symmetrix