This article explains the limit of number of logical units per physical interface on a DPC (Dense Port Concentrator) card.

When an interface is configured for more than 4095 logical units with VLAN encapsulation, the message "limit of 4096 vlans/dlcis exceeded" is reported.


Example:
In this configuration, ge-6/0/0 is on a DPC.

user@host# run show chassis hardware detail | match fpc
FPC 6 REV 16 750-022765 XL3188 DPCE 20x 1GE + 2x 10GE R
FPC 7 REV 28 750-031090 YC7842 MPC Type 2 3D EQ
FPC 8 REV 22 750-031089 ZN5936 MPC Type 2 3D
FPC 11 REV 19 750-024064 CAAP5728 MS-DPC

[edit]
user@host#

The ge-6/0/0 interface is configured for 4095 logical units with a unique combination of outer and inner vlan-tags:

[edit]
user@host# show interfaces ge-6/0/0
flexible-vlan-tagging;
unit 0 {
vlan-tags outer 1 inner 0;
}
unit 1 {
vlan-tags outer 1 inner 1;
}
unit 2 {
vlan-tags outer 1 inner 2;
}
unit 3 {
vlan-tags outer 1 inner 3;
}
unit 4 {
vlan-tags outer 1 inner 4;
}

<<<<<<<<<<<<<< snip >>>>>>>>>>>>>>>>

unit 4091 {
vlan-tags outer 1 inner 4091;
}
unit 4092 {
vlan-tags outer 1 inner 4092;
}
unit 4093 {
vlan-tags outer 1 inner 4093;
}
unit 4094 {
vlan-tags outer 1 inner 4094;
}

It is observed that all these units are created:

user@host# run show interfaces terse ge-6/0/0
Interface Admin Link Proto Local Remote
ge-6/0/0 up up
ge-6/0/0.0 up up multiservice
ge-6/0/0.1 up up multiservice
ge-6/0/0.2 up up multiservice
ge-6/0/0.3 up up multiservice
ge-6/0/0.4 up up multiservice
ge-6/0/0.5 up up multiservice
ge-6/0/0.6 up up multiservice
ge-6/0/0.7 up up multiservice
ge-6/0/0.8 up up multiservice
ge-6/0/0.9 up up multiservice
ge-6/0/0.10 up up multiservice
ge-6/0/0.11 up up multiservice
ge-6/0/0.12 up up multiservice

<<<<<<<<<<<<<< snip >>>>>>>>>>>>>>>>

ge-6/0/0.4090 up up multiservice
ge-6/0/0.4091 up up multiservice
ge-6/0/0.4092 up up multiservice
ge-6/0/0.4093 up up multiservice
ge-6/0/0.4094 up up multiservice
ge-6/0/0.32767 up up multiservice

However, when one attempts to create unit 4095 (the 4096th unit), it is observed that, the unit is not created, and a log message is reported:

[edit]
user@host# show | compare
Oct 18 09:36:41
[edit interfaces ge-6/0/0]
+ unit 4095 {
+ vlan-tags outer 2 inner 0;
+ }

[edit]
user@host# commit
Oct 18 09:36:58
commit complete

Oct 18 09:37:08 host /kernel: ge-6/0/0: limit of 4096 vlans/dlcis exceeded(1)
Oct 18 09:37:08 host /kernel: ifl_request:Unable to NULL the ifstate ptr for failed ifl on patricia tree
Oct 18 09:37:08 host dcd[1241]: DCD_CONFIG_WRITE_FAILED: IFL ge-6/0/0.4094 configuration write failed for an IFL ADD: No space left on device

It is also observed that the unit 4095 is not created :

[edit]
user@host# run show interfaces terse ge-6/0/0.4095
Oct 18 10:08:10
error: interface ge-6/0/0.4095 not found

[edit]
user@host#

The limit of number of units or VLANs that can be created per physical interface on a DPC card is 4096.  However, one of those logical units (32767) is created to accept untagged packets that come in on an interface. Therefore, the limit is 4095 configurable logical units.

When units starting from logical unit 0 thru logical unit 4094 are created, it results into a total of 4095 units. When you add the default logical unit 32767 which is already created, the total count to be 4096. If a user then configures another logical unit 4095, it will not be created and following log message will be reported:

limit of 4096 vlans/dlcis exceeded(1)

This limit applies to the count of logical units that can be created on an interface, but there is no restriction on the logical unit number to be configured.  For example, a user can create a logical unit 4095 as the first unit for that interface and it will be created without any error.

A commit error is not possible when this limit is reached because this count varies on different platforms. This is per-design, and there is no work-around.
This limit is valid for all DPC cards. This limit applies to all aggregate bundles that have a child interface on a DPC card .