Concept Guide

INTERFACE mode
flowcontrol {rx [off | on] tx [off | on] [negotiate] | monitor session-ID}
– 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. 40 gigabit Ethernet interfaces do not support pause-negotiation.
– monitor session-ID: Enter the keyword monitor then the session–ID to enable mirror ow control frames on the port. The
session–ID range is from 1 to 65535.
Congure the MTU Size on an Interface
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 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 EMC Networking OS and the number of bytes.
The MTU range is from 592 to 9216, with a default of 9216. IP MTU automatically congures.
The following table lists the various Layer 2 overheads found in the Dell EMC Networking OS and the number of bytes.
Table 43. Layer 2 Overhead
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.
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 dierent Link MTU values. Tagged members must have a link MTU 4–bytes higher than untagged members to
account for the packet tag.
Interfaces
463