Re: A good link for MPLS

A FEC is indeed as you say the combination of a couple values (Dst IP,
BGP Next Hop, IP Prec). These FEC's are just terms for clarification.
It's not a technology.

A router generates and advertises labels for each IGP learned prefix
it knows of. That way you have determined your Destination IP's
(prefixes) and BGP next hops (loopbacks from routers). The IP
precedence value is copied to the EXP field in the MPLS header, so
there are all your deviations of FEC's.

Again the FEC is a term to let you understand on how traffic is
matched in t he router when send out to be label switched (most times
on destination subnet or BGP next hop). Different FEC's could have the
same label, this is because when only the IP Precedence is different,
the EXP field is different, but the label is the same as this is based
on Destination subnet or BGP next hop.

THe label is definitely not the same throughout the network (cloud),
these label values are generated per router and could be all the same
or all different.

-- 
Regards,
Rick Mur
CCIE2 #21946 (R&S / Service Provider)
Sr. Support Engineer  IPexpert, Inc.
URL: http://www.IPexpert.com
On 10 nov 2009, at 18:19, Naufal Jamal wrote:
>
> Hi Friends,
>
> Found the below link interesting for a MPLS beginner.check it out.
>
> http://www.cisco.com/en/US/tech/tk436/tk428/tsd_technology_support_protocol_h
> ome.html
>
> I do have a doubt regrding FEC.
>
> FEC tells the first ingress router how to forward a particular  
> packet based on
> certain criteria eg.destination ip subnet,BGP next hop,IP precedence  
> value
> etc.all the packets who match the criteria are forwarded the same  
> way through
> out the cloud.
>
> how these criterias are defined or recognised by the router ? are  
> these being
> done by manipulating the EXP bits inside a label?
>
> if i am correct, then all packets in a fec have same label but all  
> same labels
> are not neccesarily under the same FEC.
>
> Kindly clarify or provide any link which could clarify the concept  
> of FEC as I
> am a beginner to MPLS..
>
> Thanks
> Naufal
>
>
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