Re: [mpls-linux-general] Some questions

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

Javier,

Thank you for trying MPLS Linux.  I've answered your questions in-line.
Please continue to send any questions you have to the mpls-linux-general
mailing list and I or others will do our best to answer your questions.

On Fri, Feb 15, 2008 at 03:55:47PM +0100, Javier Lorenzo wrote:
> First of all, I'm working with mpls-1.950 on fc4 and I think these
> things aren't working well.
> I don't know if they work on newer releases.
> 
> 1.
> I can add instructions to labelspace 0, but I can't to others:
> [root@localhost ~]# mpls ilm add label gen 100 labelspace 0
> instructions forward 0x2
> [root@localhost ~]# mpls ilm add label gen 100 labelspace 2
> instructions forward 0x2
> RTNETLINK answers: No such process

I encourage you to upgrade to Fedora 7 or 8 and use the latest
packages available.

    [root@mpls8-1 ~]# mpls ilm add label gen 100 labelspace 2
    [root@mpls8-1 ~]# mpls ilm add label gen 100 labelspace 0
    [root@mpls8-1 ~]# mpls ilm show
    ILM entry label gen 100 labelspace 0 proto ipv4 
            pop peek  (0 bytes, 0 pkts)
    ILM entry label gen 100 labelspace 2 proto ipv4 
            pop peek  (0 bytes, 0 pkts)
    [root@mpls8-1 ~]# uname -a
    Linux mpls8-1 2.6.23.15-137.fc8.mpls.1.960 #1 SMP Thu Feb 14 00:08:42 EST 2008 i686 i686 i386 GNU/Linux
    [root@mpls8-1 ~]# 

> 2.
> I have a problem when I try to add a label to a packet that already
> carries one (only one).
> In the LSR, I do:
> mpls nhlfe add key 0 instructions push gen 2000 nexthop eth0 ipv4 10.6.44.6
> mpls ilm add label gen 1000 instructions forward 0x2
> 
> And in the ingress LER I do:
> mpls nhlfe change key 0x2 instructions push gen 500 push gen 1000
> nexthop eth0 ipv4 10.6.44.2
> or:
> mpls nhlfe change key 0x2 instructions push gen 1000 nexthop eth0 ipv4 10.6.44.2
> 
> In the first case, there isn't any problems, but in the second, the S
> bit in the MPLS header
> with the label 2000 is set to 1. And it must be 0.
> I know that I can pop the label 1000 and push it again, solving the
> problem; but if I want
> to merge some LSP in that tunnel, I have to repeat the nhlfe line for each LSP.
> And I think it isn't the desired behaviour.

push without pop is not supported and it against RFC 3031.  By doing
a push without pop your exposing nodes further along the LSP to labels
they have not assigned.

       A ----> B -----> C    

In this picture the arrows represent the direction the packets are flowing.
Currently the only form of label allocation that is standardized is down
stream label allocation which mean the next hop peer assigns the label
on which a MPLS speaker can sent traffic.  In other words, B assigns labels
for which A can send traffic to B.  By doing a push without pop, you are
exposing some node beyond B to labels for which it did do assign.

If you are trying to accomplish label stacking such as is found in MPLS BGP
VPNs or by-pass tunnels, then you will want to utilize the the 'forward'
instruction on a NHLFE to product layers of indirection.

ILM (peek,pop,fwd) -> NHLFE (push,fwd) -> NHLFE (push,nexthop)


> 3.
> I don't know how to use
> set-rx-if <NAME> forward <KEY>
> I tried this:
> [root@localhost ~]# mpls ilm add label gen 255 instructions set-rx-if
> eth0 forward 0x2
> RTNETLINK answers: Operation not permitted

set-rx-if is used to set the interface you want to the kernel to believe
the packet arrived on.  It can be used in combination with the MPLS tunnel
interface to provide a bi-direction interface (MPLS tunnel interfaces are
uni-directional since they represent a uni-directional LSP).

I believe set-rx-if must be the last instruction.

> Thank you.
> -- 
> Javier Lorenzo
> 
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-- 
James R. Leu
jl...@mi...