class value in label

[vdineshkumar83]

Hi Guys,

  Came across some doc for DSCP on MPLs which states label can carry class values and  mpls EXP bits carry drop value. If thats the case how can i see the class value in label and here are they mentioning 20 bits label? And is there any pre-defined values DSCP to EXP  values?

Regards,

V Dinesh Kumar

[shivlu jain]

In MPLS we are having only 3 bit which means not more than 8 combinations of offering class of service. If you want to map DSCP to MPLS QOS then you can imagine mappings will like 0-7 DSCP belongs to MPLS EXP bit 1 then 8 to 15 DSCO belongs to 2 and upto 64.

regards

shivlu jain

http://www.mplsvpn.info

[inderdeeps]

Hello Dinesh,

We have specific combination of the 3 bits in EXP, For there combination we have the DSCP range from 0 to 63.We are defining the Class of the label as follows:-

Code Point	Forwarding Class	Loss Priority
000	best-effort	low
001	best-effort	high
010	expedited-forwarding	low
011	expedited-forwarding	high
100	assured-forwarding	low
101	assured-forwarding	high
110	network-control	low
111	network-control	high

But in actual the Diffserv model uses 6 bits of IP tos value to define the Diffserv code points(DSCP) which distinguishes how packet can be treated by the network. The first 3 bits are of EXP bits and the other 3 bits are provided by the Service Provider named as IP prec Bits, so we have two modes now:-

• Default A  simple best-effort class, with a DSCP value of 000000. Packets with no  defined DSCP are mapped to the default class for best-effort service.

• Class  Selector Provides for backward compatibility with 3-bit IP PREC  classes. Basically, it defines a DCSP of XXX000,  where XXX represent the PREC bits.

For further, Pls go through the below link:-

http://www.atslog.dp.ua/ch04lev1sec5.html

Cheers!!!

Inderdeep

[Giuseppe Larosa]

Hello Dinesh,

you are probably referring to E LSPs versus L LSPs idea

to be able to map the 6 bits wide DSCP you need to use multiple LSPs with the same destination

see the following document from networkers 2008

http://www.cisco.com/en/US/prod/collateral/iosswrel/ps6537/ps6557/ps6607/prod_presentation0900aecd8031280f.pdf

silde 6

Hope to help

Giuseppe