Information About FSPF
Fabric Shortest Path First (FSPF) is the standard path selection protocol used by Fibre Channel fabrics. The FSPF feature is enabled by default on all Fibre Channel switches. Except in configurations that require special consideration, you do not need to configure any FSPF services. FSPF automatically calculates the best path between any two switches in a fabric. FSPF provides these features:
- Dynamically compute routes throughout a fabric by establishing the shortest and quickest path between any two switches.
- Select an alternative path in the event of the failure of a given path. FSPF supports multiple paths and automatically computes an alternative path around a failed link. It provides a preferred route when two equal paths are available.
FSPF is the protocol currently standardized by the T11 committee for routing in Fibre Channel networks. The FSPF protocol has the following characteristics and features:
- Supports multipath routing.
- Bases path status on a link state protocol.
- Routes hop by hop, based only on the domain ID.
- Runs only on E ports or TE ports and provides a loop free topology.
- Runs on a per VSAN basis. Connectivity in a given VSAN in a fabric is guaranteed only for the switches configured in that VSAN.
- Uses a topology database to keep track of the state of the links on all switches in the fabric and associates a cost with each link.
- Guarantees a fast reconvergence time in case of a topology change. Uses the standard Dijkstra algorithm, but there is a static dynamic option for a more robust, efficient, and incremental Dijkstra algorithm. The reconvergence time is fast and efficient as the route computation is done on a per VSAN basis.
This section includes the following topics:
FSPF Global Configuration
By default, FSPF is enabled on switches in the Cisco MDS 9000 Family.
Some FSPF features can be globally configured in each VSAN. By configuring a feature for the entire VSAN, you do not have to specify the VSAN number for every command. This global configuration feature also reduces the chance of typing errors or other minor configuration errors.
Note FSPF is enabled by default. Generally, you do not need to configure these advanced features.
Caution
The default for the backbone region is 0 (zero). You do not need to change this setting unless your region is different from the default. If you are operating with other vendors using the backbone region, you can change this default to be compatible with those settings.
About SPF Computational Hold Times
The SPF computational hold time sets the minimum time between two consecutive SPF computations on the VSAN. Setting this to a small value means that FSPF reacts faster to any fabric changes by recomputing paths on the VSAN. A small SPF computational hold time uses more switch CPU time.
About Link State Record Defaults
Each time a new switch enters the fabric, a link state record (LSR) is sent to the neighboring switches, and then flooded throughout the fabric. Table 1-1 displays the default settings for switch responses.
Table 1-1 LSR Default Settings
|
|
|
Acknowledgment interval (RxmtInterval) |
5 seconds |
The time a switch waits for an acknowledgment from the LSR before retransmission. |
Refresh time (LSRefreshTime) |
30 minutes |
The time a switch waits before sending an LSR refresh transmission. |
Maximum age (MaxAge) |
60 minutes |
The time a switch waits before dropping the LSR from the database. |
The LSR minimum arrival time is the period between receiving LSR updates on this VSAN. Any LSR updates that arrive before the LSR minimum arrival time are discarded.
The LSR minimum interval time is the frequency at which this switch sends LSR updates on a VSAN.
About FSPF Link Cost
FSPF tracks the state of links on all switches in the fabric, associates a cost with each link in its database, and then chooses the path with a minimal cost. The cost associated with an interface can be administratively changed to implement the FSPF route selection. The integer value to specify cost can range from 1 to 65,535. The default cost for 1 Gbps is 1000 and for 2 Gbps is 500.
About Hello Time Intervals
You can set the FSPF Hello time interval to specify the interval between the periodic hello messages sent to verify the health of the link. The integer value can range from 1 to 65,535 seconds.
Note This value must be the same in the ports at both ends of the ISL.
About Dead Time Intervals
You can set the FSPF dead time interval to specify the maximum interval for which a hello message must be received before the neighbor is considered lost and removed from the database. The integer value can range from 1 to 65,535 seconds.
Note This value must be the same in the ports at both ends of the ISL.
Caution
An error is reported at the command prompt if the configured dead time interval is less than the hello time interval.
About Retransmitting Intervals
You can specify the time after which an unacknowledged link state update should be transmitted on the interface. The integer value to specify retransmit intervals can range from 1 to 65,535 seconds.
Note This value must be the same on the switches on both ends of the interface.
About Disabling FSPF for Specific Interfaces
You can disable the FSPF protocol for selected interfaces. By default, FSPF is enabled on all E ports and TE ports. This default can be disabled by setting the interface as passive.
Note FSPF must be enabled at both ends of the interface for the protocol to work.
FSPF Routes
FSPF routes traffic across the fabric, based on entries in the FSPF database. These routes can be learned dynamically, or configured statically.
About Fibre Channel Routes
Each port implements forwarding logic, which forwards frames based on its FC ID. Using the FC ID for the specified interface and domain, you can configure the specified route (for example FC ID 111211 and domain ID 3) in the switch with domain ID 1 (see Figure 1-1).
Figure 1-1 Fibre Channel Routes
Note Other than in VSANs, runtime checks are not performed on configured and suspended static routes.
About Broadcast and Multicast Routing
Broadcast and multicast in a Fibre Channel fabric uses the concept of a distribution tree to reach all switches in the fabric.
FSPF provides the topology information to compute the distribution tree. Fibre Channel defines 256 multicast groups and one broadcast address for each VSAN. Switches in the Cisco MDS 9000 Family only use broadcast routing. By default, they use the principal switch as the root node to derive a loop-free distribution tree for multicast and broadcast routing in a VSAN.
Caution
All switches in the fabric should run the same multicast and broadcast distribution tree algorithm to ensure the same distribution tree.
To interoperate with other vendor switches (following FC-SW3 guidelines), the Cisco SAN-OS and Cisco NX-OS Release 4.1(1b) and later releases uses the lowest domain switch as the root to compute the multicast tree in interop mode.
About Multicast Root Switch
By default, the native (non-interop) mode uses the principal switch as the root. If you change the default, be sure to configure the same mode in all switches in the fabric. Otherwise, multicast traffic could encounter potential loop and frame-drop problems.
Note The operational mode can be different from the configured interop mode. The interop mode always uses the lowest domain switch as the root.
In-Order Delivery
In-order delivery (IOD) of data frames guarantees frame delivery to a destination in the same order that they were sent by the originator.
Some Fibre Channel protocols or applications cannot handle out-of-order frame delivery. In these cases, switches in the Cisco MDS 9000 Family preserve frame ordering in the frame flow. The source ID (SID), destination ID (DID), and optionally the originator exchange ID (OX ID) identify the flow of the frame.
On any given switch with IOD enabled, all frames received by a specific ingress port and destined to a certain egress port are always delivered in the same order in which they were received.
Use IOD only if your environment cannot support out-of-order frame delivery.
Tip If you enable the in-order delivery feature, the graceful shutdown feature is not implemented.
About Reordering Network Frames
When you experience a route change in the network, the new selected path may be faster or less congested than the old route.
Figure 1-2 Route Change Delivery
In Figure 1-2, the new path from Switch 1 to Switch 4 is faster. In this scenario, Frame 3 and Frame 4 may be delivered before Frame 1 and Frame 2.
If the in-order guarantee feature is enabled, the frames within the network are treated as follows:
- Frames in the network are delivered in the order in which they are transmitted.
- Frames that cannot be delivered in order within the network latency drop period are dropped inside the network.
About Reordering PortChannel Frames
When a link change occurs in a PortChannel, the frames for the same exchange or the same flow can switch from one path to another faster path.
Figure 1-3 Link Congestion Delivery
In Figure 1-3, the port of the old path (red dot) is congested. In this scenario, Frame 3 and Frame 4 can be delivered before Frame 1 and Frame 2.
The in-order delivery feature attempts to minimize the number of frames dropped during PortChannel link changes when the in-order delivery is enabled by sending a request to the remote switch on the PortChannel to flush all frames for this PortChannel.
Note Both switches on the PortChannel must be running Cisco SAN-OS Release 3.0(1) for this IOD enhancement. For earlier releases, IOD waits for the switch latency period before sending new frames.
When the in-order delivery guarantee feature is enabled and a PortChannel link change occurs, the frames crossing the PortChannel are treated as follows:
- Frames using the old path are delivered before new frames are accepted.
- The new frames are delivered through the new path after the switch latency drop period has elapsed and all old frames are flushed.
Frames that cannot be delivered in order through the old path within the switch latency drop period are dropped. See the “Configuring the Drop Latency Time” section.
About Enabling In-Order Delivery
You can enable the in-order delivery feature for a specific VSAN or for the entire switch. By default, in-order delivery is disabled on switches in the Cisco MDS 9000 Family.
Tip We recommend that you only enable this feature when devices that cannot handle any out-of-order frames are present in the switch. Load-balancing algorithms within the Cisco MDS 9000 Family ensure that frames are delivered in order during normal fabric operation. The load-balancing algorithms based on source FC ID, destination FC ID, and exchange ID are enforced in hardware without any performance degradation. However, if the fabric encounters a failure and this feature is enabled, the recovery will be delayed because of an intentional pausing of fabric forwarding to purge the fabric of resident frames that could potentially be forwarded out-of-order.
About Flow Statistics
If you enable flow counters, you can enable a maximum of 1 K entries for aggregate flow and flow statistics for Generation 1 modules, and 2 K entries for Generation 2 modules. Be sure to assign an unused flow index to a module for each new flow. Flow indexes can be repeated across modules. The number space for flow index is shared between the aggregate flow statistics and the flow statistics.
Generation 1 modules allow a maximum of 1024 flow statements per module. Generation 2 modules allow a maximum of 2048-128 flow statements per module.
Note For each session, fcflow counter will increment only on locally connected devices and should be configured on the switch where the initiator is connected.
Configuring FSPF
This section includes the following topics:
Configuring FSPF on a VSAN
Detailed Steps
To configure an FSPF feature for the entire VSAN, follow these steps:
Step 1 Expand a Fabric, expand a VSAN and select FSPF for a VSAN that you want to configure for FSPF.
You see the FSPF configuration in the Information pane.
Step 2 The RegionID, Spf Comp Holdtime, LSR Min Arrival, and LSR Min Interval field values are applied across all interfaces on the VSAN. You can change them here or, if they do not exist create them here.
Step 3 Click Apply Changes to save these changes, or click Undo Changes to discard any unsaved changes.
Resetting FSPF to the Default Configuration
Detailed Steps
To return the FSPF VSAN global configuration to its factory default, follow these steps:
Step 1 Expand a Fabric, expand a VSAN, and select FSPF for a VSAN that you want to configure for FSPF.
You see the FSPF configuration in the Information pane.
Step 2 Check the SetToDefault check box for a switch.
Step 3 Click Apply Changes to save these changes, or click Undo Changes to discard any unsaved changes.
Enabling or Disabling FSPF
Detailed Steps
To enable or disable FSPF, follow these steps:
Step 1 Expand a Fabric, expand a VSAN, and select FSPF for a VSAN that you want to configure for FSPF.
You see the FSPF configuration in the Information pane.
Step 2 Set the Status Admin drop-down menu to up to enable FSPF or to down to disable FSPF.
Step 3 Click Apply Changes to save these changes, or click Undo Changes to discard any unsaved changes.
Configuring FSPF Link Cost
Detailed Steps
To configure FSPF link cost, follow these steps:
Step 1 Expand Switches, expand FC Interfaces, and then select Physical.
You see the interface configuration in the Information pane.
Step 2 Click the FSPF tab.
You see the FSPF interface configuration in the Information pane.
Step 3 Double-click in the Cost field of a switch and change the value.
Step 4 Click Apply Changes to save these changes, or click Undo Changes to discard any unsaved changes.
Configuring Hello Time Intervals
Detailed Steps
To configure the FSPF Hello time interval, follow these steps:
Step 1 Expand Switches, expand FC Interfaces, and then select Physical.
You see the interface configuration in the Information pane.
Step 2 Click the FSPF tab.
You see the FSPF interface configuration in the Information pane.
Step 3 Change the Hello Interval field for a switch.
Step 4 Click Apply Changes to save these changes, or click Undo Changes to discard any unsaved changes.
Configuring Dead Time Intervals
Detailed Steps
To configure the FSPF dead time interval, follow these steps:
Step 1 Expand Switches, expand FC Interfaces, and then select Physical.
You see the interface configuration in the Information pane.
Step 2 Click the FSPF tab.
You see the FSPF interface configuration in the Information pane.
Step 3 Double-click the Dead Interval field for a switch and provide a new value.
Step 4 Click Apply Changes to save these changes, or click Undo Changes to discard any unsaved changes.
Configuring Retransmitting Intervals
Detailed Steps
To configure the FSPF retransmit time interval, follow these steps:
Step 1 Expand Switches, expand FC Interfaces, and then select Physical.
You see the interface configuration in the Information pane.
Step 2 Click the FSPF tab.
You see the FSPF interface configuration in the Information pane.
Step 3 Double-click the ReTx Interval field and enter a value.
Step 4 Click Apply Changes to save these changes, or click Undo Changes to discard any unsaved changes.
Disabling FSPF for Specific Interfaces
You can disable the FSPF protocol for selected interfaces. By default, FSPF is enabled on all E ports and TE ports. This default can be disabled by setting the interface as passive.
You can disable the FSPF protocol for selected interfaces. By default, FSPF is enabled on all E ports and TE ports. This default can be disabled by setting the interface as passive.
Detailed Steps
To disable FSPF for a specific interface, follow these steps:
Step 1 Expand Switches, expand FC Interfaces, and then select Physical.
You see the interface configuration in the Information pane.
Step 2 Click the FSPF tab.
You see the FSPF interface configuration in the Information pane.
Step 3 Set a switch Admin Status drop-down menu to down.
Step 4 Click Apply Changes to save these changes, or click Undo Changes to discard any unsaved changes.
Configuring Fibre Channel Routes
Detailed Steps
If you disable FSPF, you can manually configure a Fibre Channel route.
To configure a Fibre Channel route using Device Manager, follow these steps:
Step 1 Click FC > Advanced > Routes.
You see the FC Static Route Configuration dialog box.
Step 2 Click Create to create a static route.
You see the Create Route dialog box.
Step 3 Select the VSAN ID that you are configuring this route.
Step 4 Fill in the destination address and destination mask for the device you are configuring a route.
Step 5 Select the interface that you want to use to reach this destination.
Step 6 Select the next hop domain ID and route metric.
Step 7 Select either the local or remote radio button.
Step 8 Click Create to save these changes or click Close to discard any unsaved changes.
Setting the Multicast Root Switch
Detailed Steps
To use the lowest domain switch for the multicast tree computation, follow these steps:
Step 1 Expand a fabric, expand a VSAN, and then select Advanced for the VSAN that you want to configure FSPF on.
You see the advanced Fibre Channel configuration in the Information pane.
Step 2 Click the Multicast Root tab.
You see the multicast root configuration in the Information pane.
Step 3 Set the Config Mode drop-down menu to lowestDomainSwitch.
Step 4 Click Apply Changes to save these changes or click Undo Changes to discard any unsaved changes.
Enabling In-Order Delivery Globally
To ensure that the in-order delivery parameters are uniform across all VSANs on an Cisco MDS 9000 Family switch, enable in-order delivery globally.
Only enable in-order delivery globally if this is a requirement across your entire fabric. Otherwise, enable IOD only for the VSANs that require this feature.
Note Enable in-order delivery on the entire switch before performing a downgrade to Cisco MDS SAN-OS Release 1.3(3) or earlier.
Enabling In-Order Delivery for a VSAN
When you create a VSAN, that VSAN automatically inherits the global in-order-guarantee value. You can override this global value by enabling or disabling in-order-guarantee for the new VSAN.
Detailed Steps
To use the lowest domain switch for the multicast tree computation, follow these steps:
Step 1 Expand a fabric and select All VSANS.
Step 2 Select the Attributes tab.
You see the general VSAN attributes in the Information pane.
Step 3 Check the InOrder Delivery check box to enable IOD for the switch.
Step 4 Click Apply Changes to save these changes, or click Undo Changes to discard any unsaved changes.
Configuring the Drop Latency Time
You can change the default latency time for a network, a specified VSAN in a network, or for the entire switch.
Detailed Steps
To configure the drop latency time for a switch, follow these steps:
Step 1 Expand a fabric and select All VSANS.
You see the VSAN configuration in the Information pane.
Step 2 Click the Attributes tab.
You see the general VSAN attributes in the Information pane.
Step 3 Double-click the Network Latency field and change the value.
Step 4 Click Apply Changes to save these changes, or click Undo Changes to discard any unsaved changes.