Users Guide

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.
○ threshold: when you configure tx on, you can set the threshold values for:
▪ Number of flow-control packet pointers: the range is from 1 to 2047 (default = 75).
▪ Flow-control buffer threshold in KB: the range is from 1 to 2013 (default = 49KB).
▪ Flow-control discard threshold in KB: the range is from 1 to 2013 (default = 75KB).
▪ Buffer threshold limit for generating PAUSE frames: the range is from 1 to 4096.
▪ Offset value for generating PAUSE frames to resume traffic: the range is from 1 to 4096.
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 Dell Networking OS and the number of bytes.
The MTU range is from 592 to 9216, with a default of 9216. IP MTU automatically configures.
The following table lists the various Layer 2 overheads found in the Dell Networking OS and the number of bytes.
Table 40. 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.
For example, if the members have a link MTU of 2100 and an IP MTU 2000, the port channel’s MTU values cannot be higher than 2100 for
link MTU or 2000 bytes for IP MTU.
VLANs:
• All members of a VLAN must have the same IP MTU value.
• Members can have different Link MTU values. Tagged members must have a link MTU 4–bytes higher than untagged members to
account for the packet tag.
• The VLAN link MTU and IP MTU must be less than or equal to the link MTU and IP MTU values configured on the VLAN members.
For example, the VLAN contains tagged members with Link MTU of 1522 and IP MTU of 1500 and untagged members with Link MTU of
1518 and IP MTU of 1500. The VLAN’s Link MTU cannot be higher than 1518 bytes and its IP MTU cannot be higher than 1500 bytes.
Interfaces
351