How To Configure The Media Mtu - Juniper EX2200 Hardware Manual

How to Configure the Media MTU

Copyright © 2015, Juniper Networks, Inc.
NOTE: The actual frames transmitted also contain cyclic redundancy check
(CRC) bits, which are not part of the media MTU. For example, the media
MTU for a Gigabit Ethernet Version 2 interface is specified as 1514 bytes, but
the largest possible frame size is actually 1518 bytes; you need to consider
the extra bits in calculations of MTUs for interoperability.
The physical MTU for Ethernet interfaces does not include the 4-byte frame
check sequence (FCS) field of the Ethernet frame.
A SONET/SDH interface operating in concatenated mode has a "c" added
to the rate descriptor. For example, a concatenated OC48 interface is referred
to as OC48c.
If you do not configure an MPLS MTU, the Junos OS derives the MPLS MTU
from the physical interface MTU. From this value, the software subtracts the
encapsulation-specific overhead and space for the maximum number of
labels that might be pushed in the Packet Forwarding Engine. Currently, the
software provides for three labels of four bytes each, for a total of 12 bytes.
In other words, the formula used to determine the MPLS MTU is the following:
MPLS MTU = physical interface MTU – encapsulation overhead – 12
If you configure an MTU value by including the
interfaces interface-name unit logical-unit-number family mpls]
the configured value is used.
To modify the default media MTU size for a physical interface, include the
at the
[edit interfaces interface-name]
[edit interfaces interface-name]
mtu bytes;
If you change the size of the media MTU, you must ensure that the size is equal to or
greater than the sum of the protocol MTU and the encapsulation overhead.
NOTE: Changing the media MTU or protocol MTU causes an interface to be
deleted and added again.
You configure the protocol MTU by including the
levels:
[edit interfaces interface-name unit logical-unit-number family family]
[edit logical-systems logical-system-name interfaces interface-name unit
logical-unit-number family family]
Chapter 2: Configuration Tasks
statement at the
mtu
hierarchy level:
mtu statement at the following hierarchy
[edit
hierarchy level,
statement
mtu
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