Figure 65: Associations Between PHB ID, EXP Bits, and Traffic Classes/Colors
For signaled mapping between EXP and PHB, policies apply the EXP bits matching and setting on a per-LSP basis rather than a per-VR basis. Signaled mapping applies only when RSVP-TE is the label distribution protocol.
When traffic is mapped onto the ingress router of the LSP, the EXP bits are set according to a policy attached to the LSP. The policy corresponds to the EXP-to-PHB mapping defined for the LSP. Typically, the policy sets the EXP bits differently according to classifier lists that match on internal class/color information or on a user packet class associated with a packet.
For transit routers and egress routers along the path of the LSP, the incoming EXP bits are matched to determine the traffic class and drop preference (color red, yellow, or green). This matching is accomplished by means of a policy corresponding to the signaled EXP-to-PHB mapping that is created and attached when the LSP is established.
EXP bits are not normally changed on transit routers, but when traffic is sent out of an LSP on a transit router, the bits can be changed by the policy. Normally, however, the net effect is that the EXP-bits remain the same through the mapping sequence of EXP bits to an internal traffic class/color combination back to EXP bits, unless the traffic class/color combination is also modified by other factors.
Because the policy (which maps the EXP bits to an internal traffic class/color combination and vice versa) attached to an LSP is created according to the PHB-ID–to–EXP mapping signaled by RSVP-TE, you must configure on each router a mapping association between PHB IDs and the internal traffic class/color combinations.
The JUNOSe software automatically generates and attaches policies when tunnels are established.
Figure 65 shows the mapping associations between PHB IDs, EXP bits, and traffic class (TC)/color combination in an E-LSP case.
Figure 65: Associations Between PHB ID, EXP Bits, and Traffic Classes/Colors
Figure 66 shows the operations performed at ingress, transit, and egress systems during signaled mapping sessions.
Figure 66: Signaled Mapping
To define a policy rule that sets the EXP bits in packets to which the policy is applied:
- host1(config-policy-list)#mark-exp 5 classifier-group
claclEXP precedence 32
To create or modify an MPLS classifier control list to match on traffic class/color combination or EXP bits:
- host1(config)#mpls classifier-list be-green
traffic-class best-effort color yellow
To map the specified PHB ID to the internal traffic class/color combination:
- host1(config)#mpls diff-serv phb-id standard
45 traffic-class gold color green
To create or modify an MPLS policy:
To enable collection of policy statistics for a tunnel or LSP. Collection is disabled by default.
Policy statistics are displayed when you issue the show mpls forwarding or show mpls tunnel command, if a policy is attached and policy statistics are enabled.
To specify the traffic class for which LSP-level queues are created and the scheduler profile to be used with the queues:
- host1(config)#mpls traffic-class af1 scheduler-profile
af1-scheduler-profile
These classes originate from E-LSPs and L-LSPs (classes derived from the signaled PHB-ID) or regular LSPs (classes configured with the mpls traffic-class command)
To specify the PHB supported by a signaled tunnel:
- host1(config-if)#tunnel mpls diff-serv phb-id
standard 35 exp-bits 5
For E-LSPs, you also use this command to map the PHB to the specified exp-bits bitValue. You can repeat the command for up to eight PHB mappings.
For L-LSPs, do not use the exp-bits keyword. If you repeat the command, the most recent command overwrites the previous command.
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