Per-Subscriber Support of Maximum Transmission Unit for Dynamic Profiles

MTU Per-Subscriber for Dynamic Profiles

A dynamic profile is a set of characteristics, defined in a type of template, that you can use to provide dynamic subscriber access and services for broadband applications. These services are assigned dynamically to interfaces. You can identify subscribers statically or dynamically. To identify subscribers statically, you can reference a static VLAN interface in a dynamic profile. To identify subscribers dynamically, you need to create variables for demux interfaces that are dynamically created when the subscribers log in. Junos OS allows you to create MTU for each subscriber for dynamic profiles. The value can be static or can be represented through a new variable, $junos-interface-mtu. By default, the variable value is the MTU of the payload, that is, the MTU of the physical interface minus the VLAN header size. A specific value can be returned through the RADIUS authentication in the Framed-MTU attribute (12). The attribute includes a single value which is applied to both the inet and inet6 protocol families if both are configured with $junos-interface-mtu variable. While applying the MTU on the subscriber logical interface during dynamic profile instantiation, a check is made to ensure that the MTU of the logical interface does not exceed what is supported on its physical interface along with the family protocol overhead. The value of the static MTU should be within the acceptable MTU range. If RADIUS does not return a Framed MTU value for $junos-interface-mtu variable, the default value for interface-mtu is used. You configure this value at the [edit dynamic profiles dynamic-profiles predefined-variable-defaults] hierarchy level. If neither is provided, then the profile request is NACKed.

Benefits of Per Subscriber Support of MTU for Dynamic Profiles

• Provides network scalability if each subscriber uses different dynamic profile or different subscriber name.

• Allows each subscriber to send traffic with different traffic rate.

Limitations

The following are the limitations:

• MTU for a dynamic logical interface is applied using the same rules as static logical interfaces.

• Framed-MTU returned by RADIUS is applicable only to the authenticated session. In other words, an authenticated dynamic VLAN (DVLAN) profile affects only the MTU for the vlan logical interface, and an authenticated DHCP profile affects only the MTU for the DHCP subscriber logical interface.

• If the RADIUS does not return a value in the Framed-MTU attribute (12), the profile request is NACKed.

• A commit check ensures that the mtu is specified for inet and inet6 address family, they must both be configured as explicit values if not the same value, or both must be configured with the $junos-interface-mtu predefined variable (in which case they are set to the same value). Otherwise, the configuration is forbidden.