Dell PowerEdge FX2/FX2s - Manual (Page 106)

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.
MTU Size
The Aggregator auto-configures interfaces to use a maximum MTU size of 12,000 bytes.
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 MTU is 1400, the link MTU
must be no less than 1422.
1400-byte IP MTU + 22-byte L2 header = 1422-byte link MTU
The MTU range is 592-12000, with a default of 1554.
The table below lists out the various Layer 2 overheads found in Dell Networking OS and the number of
bytes.
Difference between Link MTU and IP MTU
Layer 2 Overhead Difference between Link MTU and IP MTU
Ethernet (untagged) 18 bytes
VLAN Tag 4 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.
106 Interfaces