Re: [mpls-linux-general] Inheriting EXP bit in tunnel cascade

[James R. L. <jl...@mi...>]

On Mon, Aug 16, 2004 at 10:02:40AM +1000, Jon...@cs... wrote:
> Dear James
> 
> > Currently the EXP bits are new for each level of the 
> > hierarchy, this is considered the 'best common practice' by 
> > those in the MPLS WG at the IETF. At one time we discussed the 
> > scenario you are talking about, the general concessus was 
> > that it was a bad idea.
> 
> I can appreciate/imagine the reasoning of this general concessus, but
> just wondering if this scenario can be done from existing mpls-linux
> implementation.

I think you can convert the EXP bits to tcindex(or nfmark) in the ILM and then
in the NHFLE convert from tcindex(or nfmark) back to EXP _before_ each push.

Something like this:

mplsadm2 -A -I gen:16:0
mplsadm2 -I gen:16:0 -i exp2tc:0:0:1:1:2:2:3:3:4:4:5:5:6:6:7:7:pop:fwd:0x2

where 0x2 is the key for this NHLFE:

mplsadm2 -A -O 0
Key: 0x2
mplsadm2 -O 0x2 -o tc2exp:0x3f:0:0:1:1:2:2:3:3:4:4:5:5:6:6:7:7:push:gen:17:tc2exp:0xf:0:0:1:1:2:2:3:3:4:4:5:5:6:6:7:7:push:gen:18:set:eth1:ipv4:1.1.1.1

The result is that in the ILM we store the EXP bits in the tcindex.  Then
before we push we set the "current EXP bits" based on the tcindex.  After
every push the "current EXP bits" are cleared.

> > But there is no reason why I cannot 
> > create a flag that allows this sort of operation to occur.  
> > Would you like this to be a flag on the ILM, on the NHLFE, or 
> > a global flag?
> 
> Personally I would like to have it done in any way convenient for you.
> But the big issue is that we are still using the old version 1.172
> because there is some other linux functionality required not available
> in 2.6 kernel. Please ignore my request if you have found it
> inappropriate...

I think your feature request is a valid one.  AS you can see this
EXP->tcindex, tcindex->EXP it a pain.  A simple flag on the NHLFE would
make this process much easier.

> Many thanks for your comments...
> 
> Cheers,
> Jonathan
> 
> 
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-- 
James R. Leu
jl...@mi...