Here's one way to solve the problem, which should result in a patch we can merge:
* Add head-of-feature-arc processing to ip4/6_lookup_inline() under control of an integer argument [which will be passed as a constant 0 or 1]. * Create a couple of new nodes “ip4-lookup-with-post-lookup-arc” [or some better name] in ip4/6_forward.c, which instantiate the head of feature arc code * Add the “…with-post-lookup-arc” nodes to the current pre-lookup rx feature arc, before the vanilla lookup nodes. * Make the …with-post-lookup-arc” nodes siblings of the normal lookup nodes, so they inherit successor arcs/indices automatically. * Add your node(s) to the post-lookup arc To make traffic flow: enable the …with-post-lookup-arc nodes in the current rx feature arc AND enable your node(s) on the post-lookup arc If done correctly, this should cost zero clock cycles in the speed path: a hard requirement. HTH… D. -----Original Message----- From: korian edeline [mailto:korian.edel...@ulg.ac.be] Sent: Thursday, January 18, 2018 6:37 AM To: Neale Ranns (nranns) <nra...@cisco.com>; Dave Barach (dbarach) <dbar...@cisco.com>; vpp-dev@lists.fd.io Subject: Re: [vpp-dev] Create an arc Hello Neale, Dave, Thanks for your answers. I would like to catch all (not on a prefix basis) traffic to-be-forwarded. - I would need the TX sw_if_index, so i think the nodes should be placed after ip4-lookup. - i have to be before ip4-rewrite, not to compute checksums 2 times. Right now, my nodes are placed before lookup, via ip4-unicast feature arc and they can be enabled/disabled via vnet_feature_enable_disable. Something similar, but after lookup, would be really convenient. Regards, Korian On 01/18/2018 11:01 AM, Neale Ranns (nranns) wrote: > Hi Korian, > > Constructing the VLIB graph between ipX-lookup and ipX-rewrite (and really to > interface-output) is best achieved by following the DPO architecture. You can > read a little about it here: > https://wiki.fd.io/view/VPP/DPOs_and_Feature_Arcs > > Step one is to implement a new DPOs to represent your two new nodes. You’ll > find many examples of DPOs in vnet/dpo/*. Step 2 is then to ‘resolve’ the IP > prefix via your DPO. The means for that is, e.g, from vnet/bier/bier_table.c: > > bt->bt_lfei = fib_table_entry_special_dpo_add(mpls_fib_index, > &pfx, > FIB_SOURCE_BIER, > > FIB_ENTRY_FLAG_EXCLUSIVE, > &dpo); > > the rather badly named EXCLUSIVE flag means the caller is providing the DPO > and so FIB has no need to perform its usual resolution. The FIB_SOURCE_BIER > identifies ‘who’ is providing the forwarding information (the DPO) and thus > the relative priority of that information. There is a simple linear priority > scheme among the sources enumerated by fib_source_t. > Step 3 is to ‘stack’ your DPOs, i.e. to form the chain/graph that will be > followed in the data-plane. The FIB API above automatically stacks the > load_balance_t DPO (which is the result of the lookup) on your DPO passed. > > note that the above provides you with ‘override’ semantics, i.e. for a given > prefix you can override (assuming your source has higher priority) the > existing forwarding information for that prefix. If instead your requirements > are to apply further rules/checks/replications on the packets before they are > forwarded using the existing information, then this is what I call > ‘interposition’. I have an outstanding patch for this: > https://gerrit.fd.io/r/#/c/9336/ > I’ll try and get it finished soon. > > The last issue to consider is whether your override or interposition needs to > affect only the prefix you specify in the call to > fib_table_entry_special_dpo_add() or to all longer mask prefixes that it > covers. For example, if you specify 10.0.0.0/24, and some other source > specifies 10.0.0.0/25 and 10.128.0.0/25 then your prefix is never matched. In > order to ‘push’ your forwarding down to all longer mask prefixes in the > sub-tree one needs to explicitly specify this. Again, this is an outstanding > patch: > https://gerrit.fd.io/r/#/c/9477/ > > > Having said all that, if what you are after Is not running your > feature on a per-prefix basis, but instead on a per-output interface > basis, then you want the ip4-output feature arc ☺ > > hth, > neale > > > -----Original Message----- > From: "Dave Barach (dbarach)" <dbar...@cisco.com<mailto:dbar...@cisco.com>> > Date: Wednesday, 17 January 2018 at 16:21 > To: korian edeline > <korian.edel...@ulg.ac.be<mailto:korian.edel...@ulg.ac.be>>, > "vpp-dev@lists.fd.io<mailto:vpp-dev@lists.fd.io>" > <vpp-dev@lists.fd.io<mailto:vpp-dev@lists.fd.io>>, "Neale Ranns (nranns)" > <nra...@cisco.com<mailto:nra...@cisco.com>> > Subject: RE: [vpp-dev] Create an arc > > Dear Korian, > > Steering traffic from ip4_lookup to <some-node> is easily accomplished > by setting the fib result [dpo->dpoi_next_node] to send matching traffic > where you want it to go. > > Add an arc from ip4/6_lookup to <some-node> by calling > vlib_node_add_next(...) to create the arc, then create fib entries with > dpoi_next_node set to the returned next_index. > > This is not a feature arc problem. Attempting to solve it as such will > cause no end of trouble. > > Neale, please jump in as needed... > > HTH... Dave > > -----Original Message----- > From: vpp-dev-boun...@lists.fd.io<mailto:vpp-dev-boun...@lists.fd.io> > [mailto:vpp-dev-boun...@lists.fd.io] On Behalf Of korian edeline > Sent: Wednesday, January 17, 2018 9:30 AM > To: vpp-dev@lists.fd.io<mailto:vpp-dev@lists.fd.io> > Subject: [vpp-dev] Create an arc > > Hi all, > > Here is the deal: > > I have 2 nodes (my-node-1, my-node-2), I would like my-node-1 to > receive packets from ip4-lookup, forwarding to either ip4-rewrite, error-drop > or my-node-2. my-node-2 should only receive from my-node-1 and forward to > ip4-rewrite or error-drop. > > If I put them BEFORE ip4-lookup, i can use pre-built arc ip4-unicast and > everything works perfect. But i figured that if i want them after ip4-lookup, > i have to create my own arc. So here is what i have, plus replacing > occurences of "ip4-unicast" by "my-arc". > > VNET_FEATURE_ARC_INIT (my_arc, static) = { > .arc_name = "my-arc, > .start_nodes = VNET_FEATURES ("ip4-lookup"), > .arc_index_ptr = &my_main.feature_arc_index }; > > What am i missing ? > > Thanks > > Korian > > _______________________________________________ > vpp-dev mailing list > vpp-dev@lists.fd.io<mailto:vpp-dev@lists.fd.io> > https://lists.fd.io/mailman/listinfo/vpp-dev > > -- Korian Edeline Université de Liège (ULg) Bât. B28 Algorithmique des Grands Systèmes Quartier Polytech 1 Allée de la Découverte 10 4000 Liège Phone: +32 4 366 56 05
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