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Complete Software Guide for Junos
Setting the Protocol MTU
Interface Ranges
1314
®
OS for EX Series Ethernet Switches, Release 10.4
Because tunnel services interfaces are considered logical interfaces, you cannot configure
the MTU setting for the physical interface. This means you cannot include the
statement at the
[edit interfaces interface-name]
types: generic routing encapsulation (
multilink services (
), and multicast (
ml-
MTU on tunnel interfaces, as described in "Setting the Protocol MTU" on page 1314.
When you initially configure an interface, the protocol maximum transmission unit (MTU)
is calculated automatically. If you subsequently change the media MTU, the protocol
MTU on existing address families automatically changes.
For a list of default protocol MTU values, see "Configuring the Media MTU" on page 1304.
To modify the MTU for a particular protocol family, include the
mtu bytes;
You can include this statement at the following hierarchy 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]
If you increase the size of the protocol MTU, you must ensure that the size of the media
MTU is equal to or greater than the sum of the protocol MTU and the encapsulation
overhead. For a list of encapsulation overhead values, see Table 203 on page 1311. If you
reduce the media MTU size, but there are already one or more address families configured
and active on the interface, you must also reduce the protocol MTU size. (You configure
the media MTU by including the
hierarchy level, as discussed in "Configuring the Media MTU" on page 1304.)
NOTE: Changing the media MTU or protocol MTU causes an interface to be
deleted and added again.
The maximum number of data-link connection identifiers (DLCIs) is determined by the
MTU on the interface. If you have keepalives enabled, the maximum number of DLCIs is
1000, with the MTU set to 5012.
The actual frames transmitted also contain cyclic redundancy check (CRC) bits, which
are not part of the MTU. For example, the default protocol MTU for a Gigabit Ethernet
interface is 1500 bytes, but the largest possible frame size is actually 1504 bytes; you
need to consider the extra bits in calculations of MTUs for interoperability.
The Junos OS allows you to group a range of identical interfaces into an interface range.
You first specify the group of identical interfaces in the interface range. Then you can
hierarchy level for the following interface
gr-
), IP-IP (
ip-
), loopback (
,
). You can, however, configure the protocol
pe-
pd-
statement at the
mtu
[edit interfaces interface-name]
Copyright © 2010, Juniper Networks, Inc.
mtu
lo-
), link services (
ls-
),
statement:
mtu
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