Chassis/FEX Discovery Policy
The chassis/FEX discovery policy determines how the system reacts when you add a new chassis or FEX. Cisco UCS Manager uses the settings in the chassis/FEX discovery policy to determine the minimum threshold for the number of links between the chassis or FEX and the fabric interconnect and whether to group links from the IOM to the fabric interconnect in a fabric port channel.
In a Cisco UCS Mini (Cisco UCS 6324 Fabric Interconnect) setup, chassis discovery policy is supported only on the extended chassis.
Chassis Links
If you have a Cisco UCS domain with some of the chassis' wired with one link, some with two links, some with four links, and some with eight links, Cisco recommends configuring the chassis/FEX discovery policy for the minimum number links in the domain so that Cisco UCS Manager can discover all chassis.
Tip |
To establish the highest available chassis connectivity in a Cisco UCS domain where Fabric Interconnect is connected to different types of IO Modules supporting different max number of uplinks, select platform max value. Setting the platform max ensures that Cisco UCS Manager discovers the chassis including the connections and servers only when the maximum supported IOM uplinks are connected per IO Module. |
After the initial discovery of a chassis, if chassis/FEX discovery policy changes are done, acknowledge IO Modules rather than the entire Chassis to avoid disruption. The discovery policy changes can include increasing the number of links between Fabric Interconnect and IO Module, or changes to the Link Grouping preference.
Make sure that you monitor for faults before and after the IO Module acknowledgement to ensure that the connectivity is restored before proceeding to the other IO Module for the chassis.
Cisco UCS Manager cannot discover any chassis that is wired for fewer links than are configured in the chassis/FEX discovery policy. For example, if the chassis/FEX discovery policy is configured for four links, Cisco UCS Manager cannot discover any chassis that is wired for one link or two links. Re-acknowledgement of the chassis resolves this issue.
The following table provides an overview of how the chassis/FEX discovery policy works in a multi-chassis Cisco UCS domain:
Number of Links Wired for the Chassis | 1-Link Discovery Policy | 2-Link Discovery Policy | 4-Link Discovery Policy | 8-Link Discovery Policy | Platform-Max Discovery Policy | ||
---|---|---|---|---|---|---|---|
1 link between IOM and fabric interconnects |
Chassis is discovered by Cisco UCS Manager and added to the Cisco UCS domain as a chassis wired with 1 link. |
Chassis connections and servers cannot be discovered by Cisco UCS Manager and are not added to the Cisco UCS domain. |
Chassis connections and servers cannot be discovered by Cisco UCS Manager and are not added to the Cisco UCS domain. |
Chassis connections and servers cannot be discovered by Cisco UCS Manager and are not added to the Cisco UCS domain. |
Chassis connections and servers cannot be discovered by Cisco UCS Manager and are not added to the Cisco UCS domain. |
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2 links between IOM and fabric interconnects |
Chassis is discovered by Cisco UCS Manager and added to the Cisco UCS domain as a chassis wired with 1 link. After initial discovery, reacknowledge the chassis and Cisco UCS Manager recognizes and uses the additional links. |
Chassis is discovered by Cisco UCS Manager and added to the Cisco UCS domain as a chassis wired with 2 link. |
Chassis connections and servers cannot be discovered by Cisco UCS Manager and are not added to the Cisco UCS domain. |
Chassis connections and servers cannot be discovered by Cisco UCS Manager and are not added to the Cisco UCS domain. |
Chassis connections and servers cannot be discovered by Cisco UCS Manager and are not added to the Cisco UCS domain. |
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4 links between IOM and fabric interconnects |
Chassis is discovered by Cisco UCS Manager and added to the Cisco UCS domain as a chassis wired with 1 link. After initial discovery, reacknowledge the chassis and Cisco UCS Manager recognizes and uses the additional links. |
Chassis is discovered by Cisco UCS Manager and added to the Cisco UCS domain as a chassis wired with 2 links. After initial discovery, reacknowledge the chassis and Cisco UCS Manager recognizes and uses the additional links. |
Chassis is discovered by Cisco UCS Manager and added to the Cisco UCS domain as a chassis wired with 4 link. |
Chassis connections and servers cannot be discovered by Cisco UCS Manager and are not added to the Cisco UCS domain. |
If the IOM has 4 links, the chassis is discovered by Cisco UCS Manager and added to the Cisco UCS domain as a chassis wired with 4 links.
If the IOM has 8 links, the chassis is not fully discovered by Cisco UCS Manager. |
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8 links between IOM and fabric interconnects |
Chassis is discovered by Cisco UCS Manager and added to the Cisco UCS domain as a chassis wired with 1 link. After initial discovery, reacknowledge the chassis and Cisco UCS Manager recognizes and uses the additional links. |
Chassis is discovered by Cisco UCS Manager and added to the Cisco UCS domain as a chassis wired with 2 links. After initial discovery, reacknowledge the chassis and Cisco UCS Manager recognizes and uses the additional links. |
Chassis is discovered by Cisco UCS Manager and added to the Cisco UCS domain as a chassis wired with 4 links. After initial discovery, reacknowledge the chassis and Cisco UCS Manager recognizes and uses the additional links. |
Chassis is discovered by Cisco UCS Manager and added to the Cisco UCS domain as a chassis wired with 8 links. |
Chassis is discovered by Cisco UCS Manager and added to the Cisco UCS domain as a chassis wired with 8 links. |
Link Grouping
For hardware configurations that support fabric port channels, link grouping determines whether all of the links from the IOM to the fabric interconnect are grouped in to a fabric port channel during chassis discovery. If the link grouping preference is set to Port Channel, all of the links from the IOM to the fabric interconnect are grouped in a fabric port channel. If set to None, links from the IOM are pinned to the fabric interconnect.
Important |
For Cisco UCS 6500 Series Fabric Interconnects, Cisco UCS 6400 Series Fabric Interconnect, the link grouping preference is always set to Port Channel. |
After a fabric port channel is created through Cisco UCS Manager, you can add or remove links by changing the link group preference and re-acknowledging the chassis, or by enabling or disabling the chassis from the port channel.
Note |
The link grouping preference only takes effect if both sides of the links between an IOM and IFM (IOM for Cisco UCS X-Series Servers) or FEX and the fabric interconnect support fabric port channels. If one side of the links does not support fabric port channels, this preference is ignored and the links are not grouped in a port channel. |
Multicast Hardware Hash
In a port channel, by default, ingress multicast traffic on any port in the fabric interconnect (FI) selects a particular link between the IOM and the fabric interconnect to egress the traffic. To reduce potential issues with the bandwidth, and to provide effective load balancing of the ingress multicast traffic, hardware hashing is used for multicast traffic. When multicast hardware hashing is enabled, all links between the IOM and the fabric interconnect in a port channel can be used for multicast traffic.
Note |
Cisco UCS 6500 Series Fabric Interconnects, andCisco UCS 6400 Series Fabric Interconnect do not support multicast hardware hashing. |
Pinning
Pinning in Cisco UCS is only relevant to uplink ports. If you configure Link Grouping Preference as None during chassis discovery, the IOM forwards traffic from a specific server to the fabric interconnect through its uplink ports by using static route pinning.
The following table showcases how pinning is done between an IOM and the fabric interconnect based on the number of active fabric links between the IOM and the fabric interconnect.
Number of Active Fabric Links |
Server slot pinned to fabric link |
---|---|
1-Link |
All the HIF ports are pinned to the active link |
2-Link |
1,3,5,7 to link-1 2,4,6,8 to link-2 |
4-Link |
1,5 to link-1 2,6 to link-2 3,7 to link-3 4,8 to link-4 |
8-Link (Applies only to 2208XP ) |
1 to link-1 2 to link-2 3 to link-3 4 to link-4 5 to link-5 6 to link-6 7 to link-7 8 to link-8 |
Only 1,2,4 and 8 links are supported. 3,5,6, and 7 links are not valid configurations.
Port-Channeling
While pinning traffic from a specific server to an uplink port provides you with greater control over the unified fabric and ensures optimal utilization of uplink port bandwidth, it could also mean excessive traffic over certain circuits. This issue can be overcome by using port channeling. Port channeling groups all links between the IOM and the fabric interconnect into one port channel. The port channel uses a load balancing algorithm to decide the link over which to send traffic. This results in optimal traffic management.
Cisco UCS supports port-channeling only through the Link Aggregation Control Protocol (LACP). For hardware configurations that support fabric port channels, link grouping determines whether all of the links from the IOM to the fabric interconnect are grouped into a fabric port channel during chassis discovery. If the Link Grouping Preference is set to Port Channel, all of the links from the IOM to the fabric interconnect are grouped in a fabric port channel. If this parameter is set to None, links from the IOM to the fabric interconnect are not grouped in a fabric port channel.
Once a fabric port channel is created, links can be added or removed by changing the link group preference and reacknowledging the chassis, or by enabling or disabling the chassis from the port channel.
Configuring the Chassis/FEX Discovery Policy
Procedure
Step 1 |
In the Navigation pane, click Equipment. |
Step 2 |
Click the Equipment node. |
Step 3 |
In the Work pane, click the Policies tab. |
Step 4 |
Click the Global Policies subtab. |
Step 5 |
In the Chassis/FEX Discovery Policy area, specify the action and the link grouping preference. |
Step 6 |
Click Save Changes. |
What to do next
To customize fabric port channel connectivity for a specific chassis, configure the chassis connectivity policy.