Dmitry, Thanks for the clarification. In a specific example, on an interface can I have both exp and dscp rewrite rules, so that
(i) I can re-write MPLS packets using exp rewrite and (ii) for ip packets (not using mpls) to re-write dscp using dscp re-write rules. I have seen errors in log messages when I use dscp re-write rule in the above scenario, saying 'invalid rewrite table type 1'. This was in J series using Junos 8.4. Cheers Shiva On Thu, Jul 30, 2009 at 6:25 PM, Dmitry Perelman <[email protected]>wrote: > 1. You can rewrite DSCP (all 6 bits) for IPv4 packets only. The restriction > that is referenced (3-bit TOS) in your example exists when the rewrite is > done on the IPv4 payload ingress to an LSP. > > 2. The link below covers how to modify the EXP and TOS bits at LSP ingress. > To sum it up: You are able to rewrite the EXP bits along with the TOS bits > only at LSP ingress (via exp rewrite rule) which makes sense because of IPv4 > payload visibility. Since you have no visibility into the IPv4 payload on > transit nodes you only have the option to rewrite the EXP bits. You do then > have the ability to rewrite the full DSCP field on the egress PE interface. > > > http://www.juniper.net/techpubs/en_US/junos9.5/information-products/topic-collections/config-guide-cos/cos-rewriting-mpls-and-ipv4-packet-headers.html#id-11667692 > > > > On Thu, Jul 30, 2009 at 11:13 AM, Shiva Shankar <[email protected]>wrote: > >> 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 >> _______________________________________________ >> juniper-nsp mailing list [email protected] >> https://puck.nether.net/mailman/listinfo/juniper-nsp >> > > _______________________________________________ juniper-nsp mailing list [email protected] https://puck.nether.net/mailman/listinfo/juniper-nsp
