Deployment Guide

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 and 40 Gig ports.
INTERFACE mode
flowcontrol rx [off | on] tx [off | on] [negotiate]
• 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.
NOTE: The default is rx o.
.
MTU Size
The Aggregator auto-congures interfaces to use a maximum MTU size of 12,000 bytes.
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 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 592-12000, with a default of 1554.
The table below lists out the various Layer 2 overheads found in Dell Networking OS and the number of bytes.
Table 10.
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.
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 congured on the channel
members.
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Interfaces