[j-nsp] re-wite rules - query

[Shiva Shankar]

Gents, Try to understand in depth re-write rules in M/J series...From JUNOS
9.5 notes I found the following:

*For every incoming packet, the ingress classifier decodes the ingress CoS
bits into a forwarding class and packet loss priority (PLP) combination. The
egress CoS information depends on which type of rewrite marker is active, as
follows: *

   - *For Multiprotocol Label Switching (MPLS) EXP and IEEE 802.1 rewrite
   markers, values are derived from the forwarding class and PLP values in
   rewrite rules. MPLS EXP and IEEE 802.1 markers are not preserved because
   they are part of the Layer 2 encapsulation. *
   - *For IP precedence and DiffServ code point (DSCP) rewrite markers, the
   marker alters the first three bits on the type-of-service (ToS) byte while
   leaving the last three bits unchanged. *

*Questions:
*
*1. Does it mean that on Juniper M series routers, I can never chnage the
last 3 bits of the TOS byte...meaning never use the full potential of the
DSCP (6 bits)?
*
*2. So, can't I use dscp and exp re-write rules for a MPLS packet entering a
LSP on a specific interface..? It means that again I can't use DSCP in MPLS
evnvironment?

*Cheers