Cisco 7609-S Software Configuration Guide - Page 758

MPLS DiffServ Tunneling Modes Chapter 42 Configuring PFC3BXL or PFC3B Mode MPLS QoS MPLS DiffServ Tunneling Modes Tunneling provides QoS the ability to be transparent from one edge of a network to the other edge of the network. A tunnel starts where there is label imposition. A tunnel ends where there is label disposition; that is, where the label is removed from the stack, and the packet goes out as an MPLS packet with a different per-hop behavior (PHB) layer underneath or as an IP packet with the IP PHB layer. For the PFC3BXL or PFC3B, there are two ways to forward packets through a network: • Short Pipe mode-In Short Pipe mode, the egress PE router uses the original packet marking instead of the marking used by the intermediate provider (P) routers. EXP marking does not propagate to the packet ToS byte. For a description of this mode, see the "Short Pipe Mode" section on page 42-32. For the configuration information, see the "Configuring Short Pipe Mode" section on page 42-35. • Uniform mode-In Uniform mode, the marking in the IP packet may be manipulated to reflect the service provider's QoS marking in the core. This mode provides consistent QoS classification and marking throughout the network including CE and core routers. EXP marking is propagated to the underlying ToS byte. For a description, see the "Uniform Mode" section on page 42-33. For the configuration procedure, see the "Configuring Uniform Mode" section on page 42-40. Both tunneling modes affect the behavior of edge and penultimate label switching routers (LSRs) where labels are put onto packets and removed from packets. They do not affect label swapping at intermediate routers. A service provider can choose different types of tunneling modes for each customer. For additional information, see "MPLS DiffServ Tunneling Modes" at this URL: http://www.cisco.com/en/US/docs/ios/12_2t/12_2t13/feature/guide/ftdtmode.html. Short Pipe Mode Short pipe mode is used when the customer and service provider are in different DiffServ domains. It allows the service provider to enforce its own DiffServ policy while preserving customer DiffServ information, which provides a DiffServ transparency through the service provider network. QoS policies implemented in the core do not propagate to the packet ToS byte. The classification based on MPLS EXP value ends at the customer-facing egress PE interface; classification at the customer-facing egress PE interface is based on the original IP packet header and not the MPLS header. Note The presence of an egress IP policy (based on the customer's PHB marking and not on the provider's PHB marking) automatically implies the Short Pipe mode. 42-32 Cisco 7600 Series Router Cisco IOS Software Configuration Guide, Release 12.2SX OL-4266-08