Service Manual

Verison Description
6.1.1.0 Introduced on the E-Series.
Usage
Information
When you enter the no mtu command, Dell Networking OS reduces the ip mtu value to 1536 bytes. To
return the IP MTU value to the default, use the no ip mtu command.
Starting with Dell Networking OS Release 9.2(0.2), the ip mtu command is not supported to configure
the IP MTU value that is used when the IP packet is fragmented. Instead of having to configure the IP
MTU value, this value is automatically computed by the software when you configure an interface. As a
result, the ip mtu command is not available for configuration. However, you can continue to specify the
link MTU value by using the mtu command.
Compensate for Layer 2 header when configuring link MTU on an Ethernet interface or Dell Networking
OS may not fragment packets. If the packet includes a Layer 2 header, the difference between the link
MTU and IP MTU (the ip mtu command) must be enough bytes to include for the Layer 2 header.
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 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.
The following describes the difference between Link MTU and IP MTU.
Layer 2
Overhead
Difference between Link MTU and IP MTU
Ethernet
(untagged)
18 bytes
VLAN Tag Tag 22 bytes
Untagged Packet
with VLAN-Stack
Header
22 bytes
Tagged Packet
with VLAN-Stack
Header
26 bytes
Related
Commands
● mtu — set the link MTU for an Ethernet interface.
ip name-server
Enter up to six IPv4 addresses of name servers. The order you enter the addresses determines the order of their use.
Syntax
ip name-server ipv4-address [ipv4-address2...ipv4-address6]
To remove a name server, use the no ip name-server ip-address command.
714 IPv4 Routing