Juniper ACX1000 Configuration Manual page 1683

Copyright © 2017, Juniper Networks, Inc.
NOTE:
If a packet whose size is larger than the configured MTU size is received on
the receiving interface, the packet is eventually dropped. The value
considered for MRU (maximum receive unit) size is also the same as the
MTU size configured on that interface.
Not all devices allow you to set an MTU value, and some devices have
restrictions on the range of allowable MTU values. You cannot configure
an MTU for management Ethernet interfaces (fxp0, em0, or me0) or for
loopback, multilink, and multicast tunnel devices.
On ACX Series routers, you can configure the protocol MTU by including
the mtu statement at the
logical-unit-number family inet]
logical-unit-number family inet6]
If you configure the protocol MTU at any of these hierarchy levels, the
configured value is applied to all families that are configured on the
logical interface.
If you are configuring the protocol MTU for both
on the same logical interface, you must configure the same value for
both the families. It is not recommended to configure different MTU size
values for inet and inet6
interface.
Starting in Release 14.2, MTU for IRB interfaces is calculated by removing
the Ethernet header overhead
the MTU is a minimum of the two values:
Configured MTU
Associated bridge domain's physical or logical interface MTU
For Layer 2 logical interfaces configured with
MTU is calculated by including 8 bytes overhead (
For Layer 2 logical interfaces configured with
calculated by including single VLAN 4 bytes overhead.
NOTE: Changing the Layer 2 logical interface option from
vlan-tagging
logical interface MTU by 4 bytes with the existing MTU size.
As a result, the Layer 2 logical interface is deleted and
re-added, and the IRB MTU is re-computed appropriately.
Chapter 41: Configuration Statements
[edit interfaces interface-name unit
or
[edit interfaces interface-name unit
hierarchy level.
inet
families that are configured on the same logical
(6(DMAC)+6(SMAC)+2(EtherType))
flexible-vlan-tagging
vlan-tagging
to or vice versa adjusts the
flexible-vlan-tagging
and families
inet6
, and
, IRB
).
SVLAN+CVLAN
, IRB MTU is
1625