Administrator Guide

arise where a sending device may transmit data faster than a destination device can accept it. The destination sends a pause frame
back to the source, stopping the sender’s transmission for a period of time.
The globally assigned 48-bit Multicast address 01-80-C2-00-00-01 is used to send and receive pause frames. To allow full duplex
ow control, stations implementing the pause operation instruct the MAC to enable reception of frames with a destination address
equal to this multicast address.
The pause frame is dened by IEEE 802.3x and uses MAC Control frames to carry the pause commands. Ethernet pause frames are
supported on full duplex only. The only conguration applicable to half duplex ports is rx o tx o.
Note that if a port is over-subscribed, Ethernet Pause Frame ow control does not ensure no loss behavior.
The following error message appears when trying to enable ow control when half duplex is already congured:
Can’t configure flowcontrol when half duplex is configure, config ignored.
The following error message appears when trying to enable half duplex and ow control conguration is on:
Can’t configure half duplex when flowcontrol is on, config ignored.
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 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
Interfaces
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