Policy-Based Tunnel Selection - Cisco NCS 5500 Series Configuration Manual

Implementing MPLS Traffic Engineering
The following figure shows a typical interlevel (IS-IS) TE Network.
Figure 10: Interlevel (IS-IS) TE Network Diagram
As shown in the
two databases for routing and TE information. For example, R3 has TE topology information related to R2,
flooded through Level-1 IS-IS LSPs plus the TE topology information related to R4, R9, and R7, flooded as
Level 2 IS-IS Link State PDUs (LSPs) (plus, its own IS-IS LSP).
Loose hop optimization allows the re-optimization of tunnels spanning multiple areas and solves the problem
which occurs when an MPLS-TE LSP traverses hops that are not in the LSP's headend's OSPF area and IS-IS
level. Interarea MPLS-TE allows you to configure an interarea traffic engineering (TE) label switched path
(LSP) by specifying a loose source route of ABRs along the path. Then it is the responsibility of the ABR
(having a complete view of both areas) to find a path obeying the TE LSP constraints within the next area to
reach the next hop ABR (as specified on the headend router). The same operation is performed by the last
ABR connected to the tailend area to reach the tailend LSR.
You must be aware of these considerations when using loose hop optimization:
• You must specify the router ID of the ABR node (as opposed to a link address on the ABR).
• When multiarea is deployed in a network that contains subareas, you must enable MPLS-TE in the
subarea for TE to find a path when loose hop is specified.
• You must specify the reachable explicit path for the interarea tunnel.

Policy-Based Tunnel Selection

Policy-Based Tunnel Selection (PBTS) is a mechanism that lets you direct traffic into specific TE tunnels
based on different classification criteria. PBTS will benefit Internet service providers (ISPs) that carry voice
and data traffic through their MPLS and MPLS/VPN networks and would have to route this traffic to provide
optimized voice service.
PBTS works by selecting tunnels based on the classification criteria of the incoming packets, which are based
on the IP precedence or differentiated services code point (DSCP), or the Type of Service (ToS) fields in the
packets. The traffic forwarding decisions are made based on the traffic classes AND the destination network
addresses instead of only considering the destination network.
Default-class configured for paths is always zero (0). If there is no TE for a given forward-class, then the
default-class (0) will be tried. If there is no default-class, then the packet is tried against the lowest configured
forward-class tunnels. PBTS supports up to seven (exp 1 - 7) EXP values associated with a single TE-tunnel.
Figure 10: Interlevel (IS-IS) TE Network Diagram, on page
MPLS Configuration Guide for Cisco NCS 5500 Series Routers, IOS XR Release 6.2.x
MPLS-TE Features - Details
55, R2, R3, R7, and R4 maintain
55