Administrator Guide

Control how the system responds to and generates 802.3x pause frames on Ethernet interfaces. The default is rx off tx off. INTERFACE
mode. flowcontrol rx [off | on] tx [off | on]| [monitor session-ID]
Where:
rx on: Processes the received flow control frames on this port.
rx off: Ignores the received flow control frames on this port.
tx on: Sends control frames from this port to the connected device when a higher rate of traffic is received.
tx off: Flow control frames are not sent from this port to the connected device when a higher rate of traffic is received.
monitor session-ID: Enables mirror flow control frames on this port.
Changes in the flow-control values may not be reflected automatically in the show interface output. To display the change, apply the
new flow-control setting, shutdown the interface using the shutdown command, enable the interface using the no shutdown
command, and use the show interface command to verify the changes.
Enabling Pause Frames
Enable Ethernet pause frames flow control on all ports on a chassis or a line card. If not, the system may exhibit unpredictable behavior.
NOTE: Changes in the flow-control values may not be reflected automatically in the show interface output. As a
workaround, apply the new settings, execute shut then no shut on the interface, and then check the running-config of
the port.
NOTE: If you disable rx flow control, Dell EMC Networking recommends rebooting the system.
The flow control sender and receiver must be on the same port-pipe. Flow control is not supported across different port-pipes.
To enable pause frames, use the following command.
• Control how the system responds to and generates 802.3x pause frames on the Ethernet ports.
INTERFACE mode
flowcontrol {rx [off | on] tx [off | on] [negotiate] }
• rx on: enter the keywords rx on to process the received flow control frames on this port.
• rx off: enter the keywords rx off to ignore the received flow control frames on this port.
• tx on: enter the keywords tx on to send control frames from this port to the connected device when a higher rate of traffic is
received.
• tx off: enter the keywords tx off so that flow control frames are not sent from this port to the connected device when a
higher rate of traffic is received.
• negotiate: enable pause-negotiation with the egress port of the peer device. If the negotiate command is not used, pause-
negotiation is disabled. 40 gigabit Ethernet interfaces do not support pause-negotiation.
Configure the MTU Size on an Interface
If a packet includes a Layer 2 header, the difference in bytes between the link MTU and IP MTU must be enough to include the Layer 2
header.
For example, for VLAN packets, if the IP MTU is 1400, the Link MTU must be no less than 1422:
1400-byte IP MTU + 22-byte VLAN Tag = 1422-byte link MTU
The following table lists the various Layer 2 overheads found in the Dell EMC Networking OS and the number of bytes.
Table 27. Layer 2 Overhead
Layer 2 Overhead Difference Between Link MTU and IP MTU
Ethernet (untagged) 18 bytes
VLAN Tag 22 bytes
Untagged Packet with VLAN-Stack Header 22 bytes
Tagged Packet with VLAN-Stack Header 26 bytes
Interfaces 331