Re: [mpls-linux-general] help required

SourceForge Headquarters 1320 Columbia Street Suite 310 San Diego, CA 92101 +1 (858) 422-6466

On Wed, Jul 07, 2004 at 08:46:22PM +0300, Muhammad R. Sami wrote:
> I am using qdiscs and tc filters to classify and queue packets at my
> ingress, and then assigning different label/EXP pairs to different flows. My
> question is that do I require to maintain my QoS policies even at the LSRs,
> also I want to maintain the EXP bits value throughout till the egress, for
> this do I have to tell the LSR to do it or by default it would swap the
> label and keep the EXP value as is.
> Regards,
> 

In a fully diffserv aware MPLS network every node (even LSRs) apply some
sort of PHB to the packets as they traverse the LSPs.  So the short answer
is yes, I would think you would want to want to install QoS policies on the
LSRs.

I have not verified this, but it is my theory that the EXP values will be
preserved at LSRs that do not interpret them.  Looking at the code it looks
like I "pop" the EXP bits from the top label and popogate then to the "pushed"
label.  I'm not sure I thought through the hierachy cases though, so if
you plan on popping or pushing more then one label your results may vary :-)

Also, after you have a working setup, I know I, and I'm sure others, would
like to see any scripts or examples of your configuration that you can provide.

Thanks

> Muhammad R. Sami 
> Research Assistant, 
> Computer Engineering Department 
> P.O.Box 354 
> King Fahd University of Petroleum & Minerals 
> Dhahran 31261 
> Saudi Arabia. 
> Tel: +96638601423 
> Cell: +96657982951 
> www.ccse.kfupm.edu.sa/sami
> -----Original Message-----
> From: mpl...@li...
> [mailto:mpl...@li...] On Behalf Of James
> R. Leu
> Sent: Wednesday, July 07, 2004 7:20 PM
> To: Rafael Paoliello Guimaraes
> Cc: mpl...@li...
> Subject: Re: [mpls-linux-general] Trying to understand mpls-linux...
> 
> Hello,
> 
> First of all it's not 'tag-switching' ;-)
> 
> Your basic understanding of what is happening is correct.
> What version of mpls linux are you working with?  I'm going to point you
> at code in 1.930.
> 
> When mpls-linux initialized (see net/mpls/mpls_init.c:mpls_init_module())
> it registers with the network stack that any packets with protocol ID
> 0x8847 are to be sent to the function net/mpls/mpls_input.c:mpls_skb_recv().
> After mpls_skb_recv() has prepared the necessary data structures and
> extracted
> the top label (not popped, just extracts) it hands the skb off to
> mpls_input().
> mpls_input() does an ILM lookup, then processes the instructions for the
> ILM.
> (one of the instructions is probably a POP) If the last instruction was DLV
> or PEEK and there are no more labels, the packet is delivered locally to
> layer 3.  If the last instruction is FWD, the packet is label switched.  The
> FWD instructions contains a pointer to the NHLFE that will push the new
> label
> and TX the skb on the outgoing interface.  The FWD instruction is built in
> net/mpls/mpls_opcode_all.c:mpls_build_opcode_fwd(), which is called when the
> users binds a ILM to a NHLFE.  mpls_build_opcode_fwd() looks up a NHLFE via
> the index the user provides.  So as you see there is not a NHLFE lookup
> while the packet is being forwarded.  The only lookup that occurs is to
> find the ILM, from that point no further lookups will occur until the packet
> hits layer 3 (or the next hop does it's ILM lookup).
> 
> I hope this give you a better understanding of how a packet gets to
> mpls_output().  Let me know if you have any further questions.
> 
> 
> On Wed, Jul 07, 2004 at 05:24:57PM +0200, Rafael Paoliello Guimaraes wrote:
> > -----BEGIN PGP SIGNED MESSAGE-----
> > Hash: SHA1
> > 
> > Hello All,
> > 
> > I am trying to figure out the basic idea of the mpls-linux
> > implementation. I have read the "MPLS for Linux Developers' Guide" but I
> > still have some doubts, in fact I didn't understand how label switching
> > is done (I think I missed the more important part!).
> > 
> > Well, as far as I understood, the device struct of network interfaces
> > are extended, so that whenever a packet arrives, a callback function
> > (mpls_in) is called. This function looks for the received label in the
> > MII radix tree and gets information about the label. Then, if the
> > packet's destination is the current node, it sends the packet to upper
> > layers. But if the packet should be forwarded, it somehow finds it's
> > output label and switchs this value in the packet. Then it sends the
> > packet to the outgoing interface.
> > 
> > Is this the correct process? How does it find new label? In what data
> > structure is it stored (I suppose it is in the MOI radix tree)? Could
> > somebody please detail me how this tag switching is done in the current
> > implementation?
> > 
> > Thank you very much!!!
> > 
> > Best regards,
> > 
> > - --
> > 
> > ===========================================
> > ~ Rafael Paoliello Guimaraes
> > ~ PhD Student - Computer Networking Group
> > ~ Department of Computer Architecture (DAC)
> > ~ Polytechnic University of Catalonia (UPC)
> > ~ Phone: +34-934017187   Fax: +34-934017055
> > ~ URL: http://people.ac.upc.es/rpaoliel
> > ===========================================
> > -----BEGIN PGP SIGNATURE-----
> > Version: GnuPG v1.2.2 (GNU/Linux)
> > Comment: Using GnuPG with Thunderbird - http://enigmail.mozdev.org
> > 
> > iD8DBQFA7BXJ8Y15Z+P2WUARAivoAKDDhqAmlMDxqt349TFOX4XzsRTkwQCfWXdV
> > zhL/opdcrMqY4Nb5QnJ3JMI=
> > =l87y
> > -----END PGP SIGNATURE-----
> > 
> > 
> > -------------------------------------------------------
> > This SF.Net email sponsored by Black Hat Briefings & Training.
> > Attend Black Hat Briefings & Training, Las Vegas July 24-29 - 
> > digital self defense, top technical experts, no vendor pitches, 
> > unmatched networking opportunities. Visit www.blackhat.com
> > _______________________________________________
> > mpls-linux-general mailing list
> > mpl...@li...
> > https://lists.sourceforge.net/lists/listinfo/mpls-linux-general
> 
> -- 
> James R. Leu
> jl...@mi...
> 
> 
> -------------------------------------------------------
> This SF.Net email sponsored by Black Hat Briefings & Training.
> Attend Black Hat Briefings & Training, Las Vegas July 24-29 - 
> digital self defense, top technical experts, no vendor pitches, 
> unmatched networking opportunities. Visit www.blackhat.com
> _______________________________________________
> mpls-linux-general mailing list
> mpl...@li...
> https://lists.sourceforge.net/lists/listinfo/mpls-linux-general
> 

-- 
James R. Leu
jl...@mi...