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Cisco MDS 9000 Family NX-OS Interfaces Configuration Guide
OL-29284-01, Release 6.x
Chapter 2 Configuring Interfaces
Information About Interfaces
Slow Drain Device Detection and Congestion Avoidance
All data traffic between end devices in a SAN fabric is carried by Fibre Channel Class 3. In some cases,
the traffic is carried by Class 2 services that use link-level, per-hop-based, and buffer-to-buffer flow
control. These classes of service do not support end-to-end flow control. When there are slow devices
attached to the fabric, the end devices do not accept the frames at the configured or negotiated rate. The
slow devices lead to ISL credit shortage in the traffic destined for these devices and they congest the
links. The credit shortage affects the unrelated flows in the fabric that use the same ISL link even though
destination devices do not experience slow drain.
This feature provides various enhancements to detect slow drain devices that are causing congestion in
the network and also provides a congestion avoidance function.
This feature is focused mainly on the edge ports that are connected to slow drain devices. The goal is to
avoid or minimize the frames being stuck in the edge ports due to slow drain devices that are causing
ISL blockage. To avoid or minimize the stuck condition, configure lesser frame timeout for the ports.
No-credit timeout drops all packets once the slow drain is detected using the configured thresholds. The
lesser frame timeout value helps to alleviate the slow drain condition that affects the fabric by dropping
the packets on the edge ports sooner than the time they actually get timed out (500 ms). This function
frees the buffer space in ISL, which can be used by other unrelated flows that do not experience slow
drain condition.
Note This feature is used mainly for edge ports that are connected to slow edge devices. Even though this
feature can be applied to ISLs as well, we recommend that you apply this feature only for edge F ports
and retain the default configuration for ISLs as E and TE ports. This feature is not supported on
Generation 1 modules.
Management Interfaces
You can remotely configure the switch through the management interface (mgmt0). To configure a
connection on the mgmt0 interface, you must configure either the IP version 4 (IPv4) parameters (IP
address, subnet mask, and default gateway) or the IP version 6 (IPv6) parameters so that the switch is
reachable.
Before you begin to configure the management interface manually, obtain the switch’s IPv4 address and
subnet mask, or the IPv6 address.
The management port (mgmt0) is autosensing and operates in full-duplex mode at a speed of
10/100/1000 Mbps. Autosensing supports both the speed and the duplex mode. On a Supervisor-1
module, the default speed is 100 Mbps and the default duplex mode is auto. On a Supervisor-2 module,
the default speed is auto and the default duplex mode is auto.
Note You need to explicitly configure a default gateway to connect to the switch and send IP packets or add a
route for each subnet.
