Reference Guide

Routing Traffic
∙ Routing overview..............................................................................................................................................................................................................107
∙ Inter-switch links.............................................................................................................................................................................................................. 109
∙ Gateway links....................................................................................................................................................................................................................... 112
∙ Routing policies.................................................................................................................................................................................................................. 114
∙ Route selection....................................................................................................................................................................................................................116
∙ Frame order delivery........................................................................................................................................................................................................117
∙ Lossless Dynamic Load Sharing on ports........................................................................................................................................................120
∙ Frame Redirection...........................................................................................................................................................................................................123
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 routing traffic, 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 protocol, 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 Fabric
Shortest Path First (FSPF). Its purpose is to ensure that a frame is not delivered to a destination after the Resource Allocation TimeOut
Value (R_A_TOV) has expired.
Fabric OS supports unicast Class 2 and Class 3 traffic, multicast, and broadcast traffic. Broadcast and multicast are supported in Class 3
only.
NOTE
Routed edge-core-edge EX_Ports can only be used in the base switch. Other logical switch constitutes in a backbone routed
base fabric cannot be in a default switch even though they are not in the routed traffic path.
Paths and route selection
Paths are possible ways to get from one switch to another. Each inter-switch link (ISL) has a metric cost based on bandwidth. The
cumulative cost is based on the sum of all costs of all traversed ISLs.
Route selection is the path that is chosen. Paths that are selected from the routing database are chosen based on the minimal cost.
FSPF
Fabric Shortest Path First (FSPF) is a link state path selection protocol that directs traffic along the shortest path between the source and
destination based upon the link cost. FSPF is also referred to as Layer 2 routing. FSPF detects link failures, determines the shortest
route for traffic, updates the routing table, provides fixed routing paths within a fabric, and maintains correct ordering of frames. FSPF
Brocade Fabric OS Administration Guide, 8.0.1
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