The MPLS WG Archive

["Gopal@Cisco" <gnaganab@cisco.com>]

Ganges,
prefix-X------Rd--------Ru--

Data packets flow from upstream to downstream towards the destination.
Ru will use the label distributed by Rd to impose/insert/swap into the
data packet. Rd will take the forwarding decision based on the label it
looks in the data packet.
So it is necessary for Ru to use the label distributed by Rd for proper
transmission.
"> Why the bindings are assigned by the downstream LSR"--> i believe you
meant labels are assigned.....

" What makes the architecture to expect aggsinement and distribution of
> label bindings from downstream to upstream not the other way?"
> 
Label distribution can happen bothways(depending on distribution
methods: unsolicited or ondemand). However, label assignement depends on
the routing table. Ru's routing table point to Rd as the next-hop for
prefix-X. Hence Ru will use the label distributed by Rd while forwarding
data to preix X. however Rd's routing entry to prefix-X will not point
to Ru as the next-hop. Hence Rd will not use the label distributed by Ru
for prefix X.

rgds,
gopal


Gangadharan Ramakrishnan wrote:
> 
> Hi,
> 
> I'm new to this MPLS domain. I have a question on MPLS Arch (rfc3031). I
> think, may be some one else might have asked this question earlier. Well,
> the question is,
> 
> Why the bindings are assigned by the downstream LSR and why not the upstream
> LSR? What makes the architecture to expect aggsinement and distribution of
> label bindings from downstream to upstream not the other way?
> 
> Thanks in advance....
> 
> Cheers,
> ganges....
> 
> _________________________________________________________________
> Get your FREE download of MSN Explorer at http://explorer.msn.com/intl.asp

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Gopal(www-tac/~gnaganab),CCIE#6209,1.408.525.9922,RP-TAC,9:00AM-5:00PM(PST)
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