Path Calculation Component

Bandwidth

Bandwidth values are planned based on services that are to pass through a tunnel. The configured bandwidth is reserved on each node through which a tunnel passes.

Affinity

An affinity is a 32-bit vector, configured on the ingress of a tunnel. It must be used together with a link administrative group attribute.

After a tunnel is assigned an affinity, a device compares the affinity with the administrative group value during link selection to determine whether a link with specified attributes is selected or not. The link selection criteria are as follows:

• The result of the IncludeAny affinity ORed administrative group value is not 0.

• The result of the ExcludeAny affinity ORed the administrative group value is 0.

IncludeAny equals the result of the affinity attribute ORed the subnet mask; ExcludeAny equals IncludeAny ORed the subnet mask; the administrative group value equals the administrative group value ORed the subnet mask.

The following rules apply:

• If some bits in the mask are 1, at least one bit in an administrative group is 1 and its corresponding bit in the affinity must be 1. If the bits in the affinity are 0s, the corresponding bits in the administrative group cannot be 1.

• If some bits in a mask are 0s, the corresponding bits in an administrative group are not compared with the affinity bits.

  The following uses the 16-digit attribute value as an example:

  Administrative group attribute: 0000 0000 1101 1011
    Affinity: 0000 1101 0000 1101
       Mask: 0000 0000 0010 1101

  The values of bits 11, 13, 14, and 16 in the mask are 1. The value of bit 11 in both the affinity and the administrative group attribute of the link is 0 (not 1). In addition, the values of bits 13 and 16 in both the affinity and the administrative group attribute of the link are 1. Therefore, the link matches the affinity of the tunnel and can be selected for the tunnel.

A network administrator can use the link administrative group and affinities to control the paths over which MPLS TE tunnels are established.

Explicit path

An explicit path used to establish a CR-LSP. Nodes to be included or excluded are specified on this path. Explicit paths are classified into the following types:

• Strict explicit path

  A hop is directly connected to its next hop on a strict explicit path. By specifying a strict explicit path, the most accurate path is provided for a CR-LSP.

  Figure 4-5 Strict explicit path
  

  For example, a CR-LSP is set up between LSRA and LSRF on the network shown in Figure 4-5. LSRA is the ingress, and LSRF is the egress. "X strict" specifies the LSR that the CR-LSP must travel through. For example, "B strict" indicates that the CR-LSP must travel through LSRB, and the previous hop of LSRB must be LSRA. "C strict" indicates that the CR-LSP must travel through LSRC, and the previous hop of LSRC must be LSRB. The procedure repeats. A path with each node specified is provided for the CR-LSP.

• Loose explicit path

  A loose explicit path contains specified nodes through which a CR-LSP must pass. Other routers that are not specified can also exist on the CR-LSP.

  Figure 4-6 Loose explicit path
  

  For example, a CR-LSP is set up over a loose explicit path between LSRA and LSRF on the network shown in Figure 4-6. LSRA is the ingress, and LSRF is the egress. "D loose" indicates that the CR-LSP must pass through LSRD and LSRD and LSRA may not be directly connected. This means that other LSRs may exist between LSRD and LSRA.

Hop limit

Hop limit is a condition for path selection during CR-LSP establishment. Similar to the administrative group and affinity attributes, a hop limit defines the number of hops that a CR-LSP allows.