Deployment Guide

Enabling Pause Frames
Enable Ethernet pause frames ow control on all ports on a chassis. If not, the system may exhibit unpredictable behavior.
NOTE: If you disable rx flow control, Dell Networking recommends rebooting the system.
The ow control sender and receiver must be on the same port-pipe. Flow control is not supported across dierent port-pipes. (also refer
to iSCSI Optimization: Operation).
NOTE: After you disable DCB, if link-level ow control is not automatically enabled on an interface, to enable ow control,
manually shut down the interface (shutdown command) and re-enable it (no shutdown command).
To enable pause frames, use the following command.
• Control how the system responds to and generates 802.3x pause frames on 10 Gig ports.
INTERFACE mode
flowcontrol rx [off | on] tx [off | on] [negotiate] [monitor session-ID]
• rx on: enter the keywords rx on to process the received ow control frames on this port.
• rx off: enter the keywords rx off to ignore the received ow 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 trac is
received.
• tx off: enter the keywords tx off so that ow control frames are not sent from this port to the connected device when a
higher rate of trac 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.
• monitor sesssion-ID: enter the keyword monitor then the session-ID to enable mirror ow control frames on the interface.
The range is from 0 to 65535.
The default is rx o.
Congure MTU Size on an Interface
If a packet includes a Layer 2 header, the dierence 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 MTU range is from 592 to 12000, with a default of 1500. IP MTU automatically congures.
The following table lists the various Layer 2 overheads found in the Dell Networking OS and the number of bytes.
Table 27.
Dierence between Link MTU and IP MTU
Layer 2 Overhead Dierence 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
Link MTU and IP MTU considerations for port channels and VLANs are as follows.
Interfaces
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