Reserve Bandwidth on an Interface

IS-IS LSPs with TE extensions contain three TLVs related to bandwidth reservation:

• The maximum bandwidth TLV indicates the maximum outbound bandwidth that can be used on the interface. Maximum bandwidth is the operating speed of the port. When calculated for a LAG, the Maximum Bandwidth is the operating speed of the primary port multiplied by the number of active ports in the LAG. This reflects the actual physical bandwidth of the interface. This TLV is not configurable by the user.
• The maximum reservable bandwidth TLV indicates the maximum bandwidth that can be reserved on the interface. By default, the maximum reservable bandwidth is the same as the maximum bandwidth for the interface. The user can optionally change the reservable bandwidth to an amount greater or less than the maximum available bandwidth of the interface. When a maximum reservable bandwidth is configured on the primary port within a LAG, the value configured applies to the entire LAG regardless of any change to the number of active ports within the LAG. By default, the maximum reservable bandwidth for the LAG is the same as its maximum bandwidth.
• The unreserved bandwidth TLV indicates the amount of bandwidth not yet reserved on the interface. This TLV consists of eight octets, indicating the amount of unreserved bandwidth (in kilobits per second) at each of eight priority levels. The octets correspond to the bandwidth that can be reserved with a hold priority of 0 through 7, arranged in increasing order, with priority 0 occurring at the start of the TLV, and priority 7 at the end of the TLV. The value in each of the octets is less than or equal to the maximum reservable bandwidth. The unreserved bandwidth TLV itself is not user-configurable, although it is affected by modifications to the reservable bandwidth on an interface, as well as changes to LSPs.

Optionally, the user can change the amount of reservable bandwidth on an MPLS-enabled interface (that is, modify the value in the maximum reservable bandwidth TLV in IS-IS TE LSPs sent out for the interface). The maximum reservable bandwidth on an MPLS-enabled interface can be configured in either of two ways: as an absolute value, or as a percentage of the total interface bandwidth.