HP Cisco MDS 9216i Cisco MDS 9000 Family Fabric Manager Configuration Guide - - Page 435

Chapter 20 Configuring Interfaces Buffer Credits Send documentation comments to [email protected] Step 1 Step 2 Step 3 Step 4 Step 5 Expand Switches > Interfaces and then select FC Physical. You see the interface configuration in the Information pane. Click the General tab and click Mode Admin. Set the Mode Admin drop-down menu to TL. (Optional) Set other configuration parameters using the other tabs. Click Apply Changes. About TL Port ALPA Caches Although TL ports cannot be automatically configured, you can manually configure entries in arbitrated loop physical address (ALPA) caches. Generally, ALPA cache entries are automatically populated when an ALPA is assigned to a device. Each device is identified by its port world wide name (pWWN). When a device is allocated an ALPA, an entry for that device is automatically created in the ALPA cache. A cache contains entries for recently allocated ALPA values. These caches are maintained on various TL ports. If a device already has an ALPA, the Cisco NX-OS software attempts to allocate the same ALPA to the device each time. The ALPA cache is maintained in persistent storage and saves information across switch reboots. The maximum cache size is 1000 entries. If the cache is full, and a new ALPA is allocated, the Cisco NX-OS software discards an inactive cache entry (if available) to make space for the new entry. See the "TL Port" section on page 20-5 for more information on TL ports. Refer to the Cisco MDS 9000 Family CLI Configuration Guide to manage the TL Port ALPA cache. Buffer Credits Fibre Channel interfaces use buffer credits to ensure all packets are delivered to their destination. This section describes the different buffer credits available on the Cisco MDS Family switches and includes the following topics: • About Buffer-to-Buffer Credits, page 20-25 • Configuring Buffer-to-Buffer Credits, page 20-26 • About Performance Buffers, page 20-26 • Configuring Performance Buffers, page 20-27 • About Extended BB_credits, page 20-27 • Configuring Extended BB_credits, page 20-28 About Buffer-to-Buffer Credits Buffer-to-buffer credits (BB_credits) are a flow control mechanism to ensure that FC switches do not run out of buffers, because switches must not drop frames. BB_credits are negotiated on a per-hop basis. The receive BB_credit (fcrxbbcredit) value may be configured for each FC interface. In most cases, you do not need to modify the default configuration. The receive BB_credit values depend on the module type and the port mode, as follows: OL-17256-03, Cisco MDS NX-OS Release 4.x Cisco MDS 9000 Family Fabric Manager Configuration Guide 20-25