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Add sonic_fib_init plugin
Signed-off-by: Longxiang Lyu <lolv@microsoft.com>
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‎docker-sonic-vpp/conf/startup.conf.tmpl‎

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@@ -247,6 +247,7 @@ plugins {
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plugin vxlan_plugin.so { enable }
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plugin tunterm_acl_plugin.so { enable }
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plugin ip_validate_plugin.so { enable }
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plugin sonic_fib_init_plugin.so { enable }
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## Enable all plugins by default and then selectively disable specific plugins
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# plugin dpdk_plugin.so { disable }

‎docker-syncd-vpp/conf/startup.conf.tmpl‎

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plugin vxlan_plugin.so { enable }
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plugin tunterm_acl_plugin.so { enable }
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plugin ip_validate_plugin.so { enable }
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plugin sonic_fib_init_plugin.so { enable }
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## Enable all plugins by default and then selectively disable specific plugins
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# plugin dpdk_plugin.so { disable }

‎vppbld/plugins/sonic_fib_init/CMakeLists.txt‎

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# Copyright (c) 2026 Microsoft and/or its affiliates.
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# Licensed under the Apache License, Version 2.0 (the "License");
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# you may not use this file except in compliance with the License.
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# You may obtain a copy of the License at:
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#
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# http://www.apache.org/licenses/LICENSE-2.0
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#
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# Unless required by applicable law or agreed to in writing, software
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# distributed under the License is distributed on an "AS IS" BASIS,
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# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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# See the License for the specific language governing permissions and
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# limitations under the License.
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add_vpp_plugin(sonic_fib_init
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SOURCES
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sonic_fib_init.c
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API_FILES
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sonic_fib_init.api
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)

‎vppbld/plugins/sonic_fib_init/FEATURE.yaml‎

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---
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name: SONiC FIB Init
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maintainer: Longxiang Lyu <lolv@microsoft.com>
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features:
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- Removes the built-in FIB_SOURCE_SPECIAL drop entry for
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240.0.0.0/4 (IPv4 class E reserved range) from the default
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IPv4 FIB at VPP startup so that SONiC-installed routes win the
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longest-prefix match instead of the hard-coded VPP drop.
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- Exposes a `sonic_fib_strip_specials { vrf_id }` binary API for
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the SAI shim to invoke after creating additional IPv4 VRFs, so
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the same cleanup is applied to user-created tables.
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description: "SONiC-specific FIB initialization adjustments"
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state: experimental

‎vppbld/plugins/sonic_fib_init/sonic_fib_init.api‎

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/*
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* Copyright (c) 2026 Microsoft and/or its affiliates.
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at:
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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option version = "1.0.0";
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/** \brief Strip the built-in FIB_SOURCE_SPECIAL drop entries that the
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plugin manages from the IPv4 FIB identified by vrf_id (table_id).
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This is intended to be called by the SAI shim immediately after
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creating a VPP IPv4 FIB table (SAI virtual_router create) so that
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SONiC-installed routes are not pre-empted by the hard-coded VPP
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drop entries (currently 240.0.0.0/4).
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@param client_index - opaque cookie to identify the sender
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@param context - sender context, to match reply w/ request
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@param vrf_id - the IPv4 table_id whose specials should be
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stripped (0 == default VRF)
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*/
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autoreply define sonic_fib_strip_specials
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{
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u32 client_index;
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u32 context;
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u32 vrf_id;
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};

‎vppbld/plugins/sonic_fib_init/sonic_fib_init.c‎

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/*
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* Copyright (c) 2026 Microsoft and/or its affiliates.
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at:
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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/*
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* sonic_fib_init: remove built-in FIB_SOURCE_SPECIAL drop entries that
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* conflict with SONiC datapath expectations.
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*
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* Background
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* ----------
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* VPP installs hard-coded drop entries into every IPv4 FIB at creation
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* time (see src/vnet/fib/ip4_fib.c :: ip4_specials[]). One of them is
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* 240.0.0.0/4 (the IPv4 "class E reserved" range) installed with
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* FIB_SOURCE_SPECIAL + FIB_ENTRY_FLAG_DROP. FIB_SOURCE_SPECIAL is the
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* highest-priority FIB source (FIB_SOURCE_FIRST in fib_source.h) and
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* cannot be overridden via the FIB API or `ip route` CLI.
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*
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* Forwarding decisions for these address ranges should be governed by
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* the routes SONiC programs into the FIB, not by a hard-coded drop in
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* VPP. Other SONiC platforms (BCM, MLNX) do not impose this filter, so
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* we strip the SPECIAL drop here to maintain cross-platform parity and
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* let SONiC-installed routes win the longest-prefix match.
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*
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* Implementation
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* --------------
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* fib_table_entry_special_remove() is C-only (not exposed by VPP's
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* built-in binary API), so the cleanup must run from inside VPP.
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*
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* - The default VRF (fib 0) is created during VPP startup before any
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* external client connects, so we strip its SPECIAL drop once via
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* VLIB_MAIN_LOOP_ENTER_FUNCTION (after all VLIB_INIT_FUNCTIONs, so
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* the FIB and its SPECIAL entry are already in place).
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*
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* - For VRFs created at runtime (SAI virtual_router create routed
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* through the SAI shim's `ip_table_add_del`), the shim invokes our
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* `sonic_fib_strip_specials` binary API immediately after the table
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* is created. The handler looks up the fib_index for the requested
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* table_id and removes the SPECIAL drop.
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*
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* Note on 224.0.0.0/4: the matching multicast drop entry is left
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* intact intentionally; SONiC does not currently require forwarding
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* into that range and removing it could affect IGMP/PIM behaviour.
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*/
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#include <vnet/vnet.h>
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#include <vnet/plugin/plugin.h>
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#include <vnet/fib/fib_table.h>
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#include <vpp/app/version.h>
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#include <sonic_fib_init/sonic_fib_init.h>
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#include <vlibapi/api.h>
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#include <vlibmemory/api.h>
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#include <sonic_fib_init/sonic_fib_init.api_enum.h>
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#include <sonic_fib_init/sonic_fib_init.api_types.h>
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#define REPLY_MSG_ID_BASE sm->msg_id_base
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#include <vlibapi/api_helper_macros.h>
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VLIB_PLUGIN_REGISTER () = {
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.version = SONIC_FIB_INIT_PLUGIN_BUILD_VER,
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.description = "SONiC FIB init: remove implicit class-E drop",
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};
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sonic_fib_init_main_t sonic_fib_init_main;
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static void
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sonic_fib_init_strip_v4 (u32 fib_index)
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{
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fib_prefix_t pfx;
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/* IPv4: 240.0.0.0/4 (class E reserved) -- drop installed by
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* ip4_fib_hash_load_specials() with FIB_SOURCE_SPECIAL. */
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clib_memset (&pfx, 0, sizeof (pfx));
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pfx.fp_proto = FIB_PROTOCOL_IP4;
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pfx.fp_len = 4;
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pfx.fp_addr.ip4.data_u32 = clib_host_to_net_u32 (0xf0000000);
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fib_table_entry_special_remove (fib_index, &pfx, FIB_SOURCE_SPECIAL);
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}
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static void
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vl_api_sonic_fib_strip_specials_t_handler (
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vl_api_sonic_fib_strip_specials_t *mp)
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{
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sonic_fib_init_main_t *sm = &sonic_fib_init_main;
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vl_api_sonic_fib_strip_specials_reply_t *rmp;
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int rv = 0;
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u32 vrf_id = ntohl (mp->vrf_id);
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u32 fib_index;
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fib_index = fib_table_find (FIB_PROTOCOL_IP4, vrf_id);
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if (fib_index == ~0)
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{
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rv = VNET_API_ERROR_NO_SUCH_FIB;
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goto done;
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}
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sonic_fib_init_strip_v4 (fib_index);
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done:
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REPLY_MACRO (VL_API_SONIC_FIB_STRIP_SPECIALS_REPLY);
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}
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/* API definitions */
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#include <sonic_fib_init/sonic_fib_init.api.c>
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static clib_error_t *
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sonic_fib_init_init (vlib_main_t *vm)
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{
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sonic_fib_init_main_t *sm = &sonic_fib_init_main;
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sm->msg_id_base = setup_message_id_table ();
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return 0;
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}
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VLIB_INIT_FUNCTION (sonic_fib_init_init);
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static clib_error_t *
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sonic_fib_init_main_loop_enter (vlib_main_t *vm)
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{
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/* fib 0 is the default VRF, created during VPP startup. Additional
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* VRFs are handled via the sonic_fib_strip_specials API. */
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sonic_fib_init_strip_v4 (0);
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return 0;
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}
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VLIB_MAIN_LOOP_ENTER_FUNCTION (sonic_fib_init_main_loop_enter);

‎vppbld/plugins/sonic_fib_init/sonic_fib_init.h‎

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/*
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* Copyright (c) 2026 Microsoft and/or its affiliates.
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at:
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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#ifndef __included_sonic_fib_init_h__
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#define __included_sonic_fib_init_h__
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#include <vnet/vnet.h>
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typedef struct
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{
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/* API message ID base */
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u16 msg_id_base;
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} sonic_fib_init_main_t;
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extern sonic_fib_init_main_t sonic_fib_init_main;
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#define SONIC_FIB_INIT_PLUGIN_BUILD_VER "1.0"
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#endif /* __included_sonic_fib_init_h__ */

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