Dell S3048-ON, Configuration Manual

Page: 349 / 1036

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.
NOTE: 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.
NOTE: 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
received.
•
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.
Configure the MTU Size on an Interface
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
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 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 Difference 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 configured on the channel
members.
Interfaces 349