Enabling Pause Frames; Configure The Mtu Size On An Interface - Dell S3048-ON Configuration Manual

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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.

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.

If you disable rx flow control, Dell 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

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.

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

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 Networking OS and the number of bytes.

Table 24. Layer 2 Overhead

Layer 2 Overhead

Ethernet (untagged)

Untagged Packet with VLAN-Stack Header

Tagged Packet with VLAN-Stack Header

Link MTU and IP MTU considerations for port channels and VLANs are as follows.

Port Channels:

All members must have the same link MTU value and the same IP MTU value.

The port channel link MTU and IP MTU must be less than or equal to the link MTU and IP MTU values configured on the channel

Difference Between Link MTU and IP MTU

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