Re: [mpls-linux-devel] Current state of dst stacking on davem implementation

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

Hey guys,

Here is my list of "issues" with the davem implementation:

-no handling of exceeding MTU, or to changes in devices MTU
-reserved label values are not restricted nor handled
-no support for flushing all ILM/NHLFE
-no handling of PUSH when SKB has no space
-tcpdump of egress LSR shows packet twice, once with MPLS header once without
-NHLFE structure has issues
    -same NLFE cannot be used by transit LSP and locally originated traffic
        -Think of LDP with ordered control where an LSR could be ingress for
         a FEC as well as transit. (LSR received label mapping, it decides it
         can be ingress for the FEC, and then propogates the mapping, result
         it that the NHLFE is tied to a route entry and well as a ILM.  ILM
         needs XCHANGE, route entry needs ADD).
    -there is no such thing as a labelspace for NHLFE, it should be removed.
    -NHLFE hashing does not allow for same label mapping to be received
     from multiple peers in the same subnet
        -Think of an LSR speaking RSVP-TE connected to a ethernet subnet
         with 2 other RSVP-TE speakers.  RSVP-TE LSPs are requested from
         each of the other RSVP-TE speakers, they both advertise back the
         same label value.
    -does not allow for re-use of NHLFE when stacking
    -extra fields which would not be used when stacking
-no support for LSP hierarchy (ingress or egress)

The "no support for LSP hierarchy" is only one element in the list, but
it is a fairly large issue.

Since I didn't want to make large changes to the davem code without discussion
I have been spending my time integrating the positive features of the davem
implementation into mine.  This consisted of adding the protocol driver
model and making better use of the the dst_entry to guide skb's through
the MPLS stack.

In the process I've:
- implemented MPLS-ICMP for IPv4 (which has been implemented by vendors,
  but is only in draft form. It works with the NANOG patch to traceroute
  to show the labelling info.)  It is kind of a hack because I build the
  entire ICMP payload by hand.  I'm looking at ways to utilize the existing
  IPv4 ICMP code. (as an aside, it is cool to use an MPLS enable traceroute
  and see all of the providers who are using MPLS :-)
- the ICMP path has been modified to allow for offending messages to be
  replace by ICMP messages and forwarded along to the end of the LSP where
  the egress can handle it.
- the refcnt'ing code has been modified to disallow removing in/out
  information when some external entitiy is holding a ref (IPv4/IPv6/MPLS
  tunnel interface)
- Begining of seperation of sysfs code.  I love the sysfs code, but it needed
  to be seperated so MPLS can be compiled without sysfs support.  The sysfs
  support also makes the implementation look more complicated then it really
  is.

I've just started adding netlink support.  My goal is to utilize all of the
netlink infrastructure Jamal added to the Davem implementation.  I want to
be userland API compliant between the implementations.

After netlink comes LSP loadbalancing (ILM based) using some of the schemes
we discussed previously.

In addition I've spent a lot of time working on a generic MPLS infrastructure
for quagga.  I'm to the point where I now need to add OS level support for
the various MPLS components.  I will make sure to write versions for
my code as well and the davem code.

I still think the best path going forward is to enhance my implementation
to be more agreeable to DaveM (I'm not sure what, if any, issues remain).
If you guys still think that the easiest path to adoption of MPLS code into
the Linux distribution is by modifing the DaveM code, I'll continue to help
out as much as possible, but we need to starting talking about making some
big changes.

No matter what. I'll still be working on my implementation, if nothing
else it is an easy place for me to implement new features which could then
be ported to the DaveM code.

On Fri, Mar 19, 2004 at 10:52:33AM -0500, Jamal Hadi Salim wrote:
> hi gents,
> I am semi back - hopefully we can get this done soon so we shoot 
> to submit?
> Where were we? ;-> 
> 
> cheers,
> jamal
> 
> 
> 
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-- 
James R. Leu
jl...@mi...