Fabric OS Administrator’s Guide 63
53-1001763-02
Chapter
4

Routing Traffic

About this chapter

•Routing overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63
•Inter-switch links . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66
•Gateway links . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69
•Inter-chassis links . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71
•Routing policies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73
•Route selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 76
•Frame order delivery . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 78
•Lossless Dynamic Load Sharing on ports . . . . . . . . . . . . . . . . . . . . . . . . . . . 79
•Frame Redirection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81

Routing overview

Data moves through a fabric from switch to switch and from storage to server along one or more
paths that make up a route. Routing policies determine the path for each frame of data.
Before the fabric can begin to route, it must discover the route a packet should take to reach the
intended destination. Route tables are lists that indicate the next hop to which packets are directed
to reach a destination. Route tables include network addresses, the next address in the data path,
and a cost to reach the destination network. There are two kinds of routing protocols on intranet
networks, Distance Vector and Link State.
•Distance Vector is based on hop count. This is the number of switches that a frame passes
through to get from the source switch to the destination switch.
•Link State is based on a metric value based on a cost. The cost could be based on bandwidth,
line speed, or round-trip-time.
With the link-state method, switches that discover a route identify the networks to which they are
attached, receiving an initial route table from the principal switch. After an initial message is sent
out, the switch only notifies the others when changes occur.
It is recommended that no more than seven hops occur between any two switches. This limit is not
required or enforced by FSPF. Its purpose is to ensure that a frame is not delivered to a destination
after R_A_TOV has expired.
Unicast, multicast, and broadcast traffic are supported. Both Unicast Class 2 and 3 traffic are
supported. Broadcast and multicast are supported in Class 3 only.