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 [edit interfaces interface-name unit
logical-unit-number family inet] or [edit interfaces interface-name unit
logical-unit-number family inet6] hierarchy level.
• 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 inet and inet6 families
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 families that are configured on the same logical
interface.
• Starting in Release 14.2, MTU for IRB interfaces is calculated by removing
the Ethernet header overhead (6(DMAC)+6(SMAC)+2(EtherType)), and
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 flexible-vlan-tagging, IRB
MTU is calculated by including 8 bytes overhead (SVLAN+CVLAN).
• For Layer 2 logical interfaces configured with vlan-tagging, IRB MTU is
calculated by including single VLAN 4 bytes overhead.
NOTE: Changing the Layer 2 logical interface option from
vlan-tagging to flexible-vlan-tagging or vice versa adjusts the
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.
1625Copyright © 2017, Juniper Networks, Inc.
Chapter 41: Configuration Statements
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