Re: [mpls-linux-general] Looking for examples to test TC/DS/IPTABLE

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

Comments below ....

On Tue, Dec 18, 2001 at 04:21:48PM +0100, Olivier Dugeon wrote:
> Hi Jim,
> 
> James R. Leu wrote:
> 
> > I see the light now.....
> > 
> > Last night I dug around the kernel and I now see why you think that
> > netfilter is the best way for interacting with the ipv4 routing table.
> > I will look more at your work and see how I can make it less MPLS specific.
> > 
> > Right now I think I am going to add a new netlink.  POST_ROUTING_SLOW.
> > This will allow a netlink to modify the route cache entry.  The result will
> > be that the netlink code for this will only be run for the first packet
> > in the "flow".    The rest will hit the entry in the route cache and
> > will be redirected to the MPLS layer.
> > 
> 
> 
> Ok, i think it's a good way setup the process of the first packet. It's 
> that we do by hacking the rt_set_nexthop code. This function is call 
> only for the first packet of a flow (ie. the first ping packet). Then, 
> the entry are kept into the route cash a moment (so, stoping a ping and 
> start some time after a second ping, doesn't call another time 
> rt_set_nexthop because the route cash entry is still valid).
> 
> What do you intend to do with this new POST_ROUTING_SLOW netlink ?

-change the pmtu
-use the some index on the skb to lookup the moi, attach it to the route cache
 entry
-change rt->dst.output to be mpls_output

This will require that everytime a moi is deleted, the route cache must
be cleared. :-(

What do you think of this?

What should be done with skb that come through POST_ROUTING_SLOW but
a moi could not be found?

1. I could drop it, then a route cache entry will not be created and
next time a packet for this flow is seen it will be slow routed again
giving another chance for a valid moi to be found.

2. I could let it pass and let it go via IP.  Also subsequent packets for
this flow will be fast routed, thus not given a chance to find valid moi.
To get around this everytime a new moi is created the route cache could
be cleared, thuis forcing packets to go through the slow path again.

What do you suggest?

Jim

> - directly setup the route cash entry or
> - setup mpls_index (or nfmark) ?
> 
> 
> > Will this satisfy your hope of avoiding double lookups (for every packet
> > except the first)?
> 
> 
> Yes.
> 
> Olivier
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-- 
James R. Leu
jl...@mi...