Interfaces | 247
Table 13-3 lists the range for each transmission media.
Layer 2 Flow Control Using Ethernet Pause Frames
Ethernet pause frames allow for a temporary stop in data transmission. A situation may 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 flow 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 defined 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 configuration applicable to half duplex
ports is
rx off tx off.
Note that if a port is over-subscribed, Ethernet Pause Frame flow control does not ensure no loss behavior.
The following error message appears when trying to enable flow control when half duplex is already
configured:
Can’t configure flowcontrol when half duplex is configure, config ignored.
The following error message appears when trying to enable half duplex and flow control configuration is
on:
Can’t configure half duplex when flowcontrol is on, config ignored.
Enable Pause Frames
You must enable the Ethernet pause frames flow control on all ports on a chassis. If not, the system may
exhibit unpredictable behavior.
Table 13-3. MTU Range
Transmission Media MTU Range (in bytes)
Ethernet 594-12000 = link MTU
576-11982 = IP MTU
Note: If rx flow control is disabled, Dell Force10 recommends rebooting the system.
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