The Path Message THE RESOURCE RESERVATION PROTOCOL RSVP

THE RESOURCE RESERVATION PROTOCOL – TRAFFIC ENGINEERING 177 • Maximum DLCI : This 23-bit field give the upper bound on the block of the supported DLCI values. In order to establish an LSP, the sender creates a Path message with a LABEL REQUEST object. This object indicates that a label binding for this path is requested and it provides an indication of the network protocol layer that is to be carried over the path. This permits packets form non-IP network layer protocols to be sent down an LSP. This information is also useful in label allocation, because some reserved labels are protocol specific. A receiver that cannot support the protocol indicated in the L3PID field, sends a PathErr message back to the sender. The EXPLICIT ROUTE object ERO This object is used to specify the hops in the requested explicit route. Each hop could be a single node or a group of nodes, referred to as an abstract node. For simplicity, RSVP-TE refers to all of the hops as abstract nodes, with the understanding that an abstract node could consist of a single node. The EXPLICIT ROUTE object class is 20, and only one object type C-Type 1 has been defined. The object contents consists of a series of variable-length sub-objects, each of which contains an abstract node. The format of the sub-object is shown in Figure 7.24. The following fields have been defined: • L : A 1-bit field used to indicate whether the route through an abstract node is loose or strict. • Type : This 7-bit field is populated with a value that indicates the type of contents of the sub-object. The following values have been defined: 0 if the sub-object contains an IPv4 prefix, 1 if it contains an IPv6 prefix, and 32 if it contains an autonomous system number. • Length : This 8-bit field is populated with the length in bytes of the sub-object including the L, type, and length fields. The format of the sub-objects for the IPv4 and IPv6 is shown in Figure 7.25. The field IPv4 address respectively IPv6 address in the IPv4 IPv6 sub-object contains an IPv4 IPv6 prefix whose length is given in the prefix length field. The abstract node represented by this sub-object is the set of all nodes whose IPv4 IPv6 address has the prefix given in the IPv4 IPv6 address field. Note that a prefix length of 128 indicates a single node. The sub-object format for the autonomous system is the same as the one shown in Figure 7.24, with the sub-object contents consisting of a two-byte field populated with the autonomous system number. The abstract node represented by this sub-object is the set of all nodes belonging to the autonomous system. 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 Length L Type Sub-object contents Figure 7.24 The format of a sub-object.