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Spirent KB Article
Doc ID: FAQ10630
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Spirent TestCenter: Where to set the EXP bits in LDP bound streams?
MPLS EXP bits
When creating the stream, before you click the Add button at the "select source and destination" window you need to check Show All Headers.
Basically the MPLS EXP bits is set by setting the IP Header TOS/Diffserv values. See attached document.
The higher order 3 bits of the IP TOS are copied to the EXP bits, irrespective of the manual changes in EXP
This is a standard behavior by default, explained in the RFC3270 section 3.5
This mapping of the IP Precedence bits to/from the MPLS EXP bits upon ingress/egress is desired to preserve QOS between the IP/MPLS network boundaries.
However with the use of modifiers in the stream configuration, we can achieve EXP value different from TOS value.
Add a modifier for DSCP and EXP fields.
Product : Routing,Windows GUI