Users Guide

The table below lists out the various Layer 2 overheads found in Dell Networking OS and the number of bytes.
Table 8. Dierence between Link MTU and IP MTU
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.
• The VLAN link MTU and IP MTU must be less than or equal to the link MTU and IP MTU values congured on the VLAN
members.
For example, the VLAN contains tagged members with a link MTU of 1522 and an IP MTU of 1500 and untagged members with a
link MTU of 1518 and an 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.
Auto-Negotiation on Ethernet Interfaces
Setting Speed and Duplex Mode of Ethernet Interfaces
By default, auto-negotiation of speed and duplex mode is enabled on 1GbE and 10GbE Ethernet interfaces on an Aggregator.
The local interface and the directly connected remote interface must have the same setting. Auto-negotiation is the easiest way to
accomplish these settings, as long as the remote interface is capable of auto-negotiation.
NOTE: As a best practice, Dell Networking recommends keeping auto-negotiation enabled. Auto-negotiation should only
be disabled on switch ports that attach to devices not capable of supporting negotiation or where connectivity issues
arise from interoperability issues.
For 100/1000/10000 Ethernet interfaces, the negotiation auto command is tied to the speed command. Auto-negotiation is always
enabled when the speed command is set to 1000 or auto. In Dell Networking OS, the speed 1000 command is an exact equivalent of
speed auto 1000 in IOS.
To discover whether the remote and local interface require manual speed synchronization, and to manually synchronize them if
necessary, follow these steps.
1. Determine the local interface status.
EXEC Privilege mode
Interfaces
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