4 This is an EXPERIMENTAL support of draft
5 `draft-ietf-ospf-segment-routing-extensions-24`.
6 DON'T use it for production network.
14 Segment Routing used 3 differents OPAQUE LSA in OSPF to carry the various
17 * **Router Information:** flood the Segment Routing capabilities of the node.
18 This include the supported algorithms, the Segment Routing Global Block
19 (SRGB) and the Maximum Stack Depth (MSD).
20 * **Extended Link:** flood the Adjaceny and Lan Adjacency Segment Identifier
21 * **Extended Prefix:** flood the Prefix Segment Identifier
23 The implementation follow previous TE and Router Information codes. It used the
24 OPAQUE LSA functions defined in ospf_opaque.[c,h] as well as the OSPF API. This
25 latter is mandatory for the implementation as it provides the Callback to
26 Segment Routing functions (see below) when an Extended Link / Prefix or Router
27 Information LSA s are received.
32 Following files where modified or added:
34 * ospd_ri.[c,h] have been modified to add the new TLVs for Segment Routing.
35 * ospf_ext.[c,h] implement RFC7684 as base support of Extended Link and Prefix
37 * ospf_sr.[c,h] implement the earth of Segment Routing. It adds a new Segment
38 Routing database to manage Segment Identifiers per Link and Prefix and
39 Segment Routing enable node, Callback functions to process incoming LSA and
40 install MPLS FIB entry through Zebra.
42 The figure below shows the relation between the various files:
44 * ospf_sr.c centralized all the Segment Routing processing. It receives Opaque
45 LSA Router Information (4.0.0.0) from ospf_ri.c and Extended Prefix
46 (7.0.0.X) Link (8.0.0.X) from ospf_ext.c. Once received, it parse TLVs and
47 SubTLVs and store information in SRDB (which is defined in ospf_sr.h). For
48 each received LSA, NHLFE is computed and send to Zebra to add/remove new
49 MPLS labels entries and FEC. New CLI configurations are also centralized in
50 ospf_sr.c. This CLI will trigger the flooding of new LSA Router Information
51 (4.0.0.0), Extended Prefix (7.0.0.X) and Link (8.0.0.X) by ospf_ri.c,
52 respectively ospf_ext.c.
53 * ospf_ri.c send back to ospf_sr.c received Router Information LSA and update
54 Self Router Information LSA with paramters provided by ospf_sr.c i.e. SRGB
55 and MSD. It use ospf_opaque.c functions to send/received these Opaque LSAs.
56 * ospf_ext.c send back to ospf_sr.c received Extended Prefix and Link Opaque
57 LSA and send self Extended Prefix and Link Opaque LSA through ospf_opaque.c
62 +-----------+ +-------+
64 | ospf_sr.c +-----+ SRDB |
65 +-----------+ +--+ | |
66 | +-^-------^-+ | +-------+
71 +---v----------+ | | | +-----v-------+
73 | ospf_ri.c +--+ | +-------+ ospf_ext.c |
74 | LSA 4.0.0.0 | | | LSA 7.0.0.X |
76 +---^----------+ | | |
80 | +--------v------------+ |
82 | | ZEBRA: Labels + FEC | |
84 | +---------------------+ |
89 +---------> ospf_opaque.c <---------+
93 Figure 1: Overview of Segment Routing interaction
98 To process incoming LSA, the code is based on the capability to call `hook()`
99 functions when LSA are inserted or delete to / from the LSDB and the
100 possibility to register particular treatment for Opaque LSA. The first point
101 is provided by the OSPF API feature and the second by the Opaque implementation
102 itself. Indeed, it is possible to register callback function for a given Opaque
103 LSA ID (see `ospf_register_opaque_functab()` function defined in
104 `ospf_opaque.c`). Each time a new LSA is added to the LSDB, the
105 `new_lsa_hook()` function previously register for this LSA type is called. For
106 Opaque LSA it is the `ospf_opaque_lsa_install_hook()`. For deletion, it is
107 `ospf_opaque_lsa_delete_hook()`.
109 Note that incoming LSA which is already present in the LSDB will be inserted
110 after the old instance of this LSA remove from the LSDB. Thus, after the first
111 time, each incoming LSA will trigger a `delete` following by an `install`. This
112 is not very helpfull to handle real LSA deletion. In fact, LSA deletion is done
113 by Flushing LSA i.e. flood LSA after seting its age to MAX_AGE. Then, a garbage
114 function has the role to remove all LSA with `age == MAX_AGE` in the LSDB. So,
115 to handle LSA Flush, the best is to look to the LSA age to determine if it is
116 an installation or a future deletion i.e. the flushed LSA is first store in the
117 LSDB with MAX_AGE waiting for the garbage collector function.
119 Router Information LSAs
120 ^^^^^^^^^^^^^^^^^^^^^^^
122 To activate Segment Routing, new CLI command `segment-routing on` has been
123 introduced. When this command is activated, function
124 `ospf_router_info_update_sr()` is called to indicate to Router Information
125 process that Segment Routing TLVs must be flood. Same function is called to
126 modify the Segment Routing Global Block (SRGB) and Maximum Stack Depth (MSD)
127 TLV. Only Shortest Path First (SPF) Algorithm is supported, so no possiblity
128 to modify this TLV is offer by the code.
130 When Opaque LSA Tyep 4 i.e. Router Information are stored in LSDB, function
131 `ospf_opaque_lsa_install_hook()` will call the previously registered function
132 `ospf_router_info_lsa_update()`. In turn, the function will simply trigger
133 `ospf_sr_ri_lsa_update()` or `ospf_sr_ri_lsa_delete` in function of the LSA
134 age. Before, it verifies that the LSA Opaque Type is 4 (Router Information).
135 Self Opaque LSA are not send back to the Segment Routing functions as
136 information are already stored.
138 Extended Link Prefix LSAs
139 ^^^^^^^^^^^^^^^^^^^^^^^^^
141 Like for Router Information, Segment Routing is activate at the Extended
142 Link/Prefix level with new `segment-routing on` command. This trigger
143 automtically the flooding of Extended Link LSA for all ospf interface where
144 adjacency is full. For Extended Prefix LSA, the new CLI command
145 `segment-routing prefix ...` will trigger the flooding of Prefix SID
148 When Opaque LSA Type 7 i.e. Extended Prefix and Type 8 i.e. Extended Link are
149 store in the LSDB, `ospf_ext_pref_update_lsa()` respectively
150 `ospf_ext_link_update_lsa()` are called like for Router Information LSA. In
151 turn, they respectively trigger `ospf_sr_ext_prefix_lsa_update()` /
152 `ospf_sr_ext_link_lsa_update()` or `ospf_sr_ext_prefix_lsa_delete()` /
153 `ospf_sr_ext_link_lsa_delete()` if the LSA age is equal to MAX_AGE.
158 When a new MPLS entry or new Forwarding Equivalent Class (FEC) must be added or
159 deleted in the data plane, `add_sid_nhlfe()` respectively `del_sid_nhlfe()` are
160 called. Once check the validity of labels, they are send to ZEBRA layer through
161 `ZEBRA_MPLS_LABELS_ADD` command, respectively `ZEBRA_MPLS_LABELS_DELETE`
162 command for deletion. This is completed by a new labelled route through
163 `ZEBRA_ROUTE_ADD` command, respectively `ZEBRA_ROUTE_DELETE` command.
171 In order to use OSPF Segment Routing, you must setup MPLS data plane. Up to
172 know, only Linux Kernel version >= 4.5 is supported.
174 First, the MPLS modules aren't loaded by default, so you'll need to load them
181 modprobe mpls_iptunnel
183 Then, you must activate MPLS on the interface you would used:
187 sysctl -w net.mpls.conf.enp0s9.input=1
188 sysctl -w net.mpls.conf.lo.input=1
189 sysctl -w net.mpls.platform_labels=1048575
191 The last line fix the maximum MPLS label value.
193 Once OSPFd start with Segment Routing, you could check that MPLS routes are
201 The first command show the MPLS LFIB table while the second show the FIB
202 table which contains route with MPLS label encapsulation.
204 If you disable Penultimate Hop Popping with the `no-php-flag` (see below), you
205 MUST check that RP filter is not enable for the interface you intend to use,
206 especially the `lo` one. For that purpose, disable RP filtering with:
210 systcl -w net.ipv4.conf.all.rp_filter=0
211 sysctl -w net.ipv4.conf.lo.rp_filter=0
216 Here it is a simple example of configuration to enable Segment Routing. Note
217 that `opaque capability` and `router information` must be set to activate
218 Opaque LSA prior to Segment
224 ospf router-id 192.168.1.11
227 mpls-te router-address 192.168.1.11
228 router-info area 0.0.0.0
230 segment-routing global-block 10000 19999
231 segment-routing node-msd 8
232 segment-routing prefix 192.168.1.11/32 index 1100
234 The first segment-routing statement enable it. The Second one set the SRGB,
235 third line the MSD and finally, set the Prefix SID index for a given prefix.
236 Note that only prefix of Loopback interface could be configured with a Prefix
237 SID. It is possible to add `no-php-flag` at the end of the prefix command to
238 disbale Penultimate Hop Popping. This advertises peers that they MUST NOT pop
239 the MPLS label prior to sending the packet.
244 * Runs only within default VRF
245 * Only single Area is supported. ABR is not yet supported
246 * Only SPF algorithm is supported
247 * Extended Prefix Range is not supported
248 * MPLS table are not flush at startup. Thus, restarting zebra process is
249 mandatory to remove old MPLS entries in the data plane after a crash of
251 * Due to a bug in OSPF Opaque, LSA are not flood when enable Segment Routing
252 through CLI once OSPFd started. You must configure Segment Routing within
253 configuration file before launching OSPFd
254 * With NO Penultimate Hop Popping, it is not possible to express a Segment
255 Path with an Adjacency SID due to the impossibility for the Linux Kernel to
256 perform double POP instruction.
261 * Author: Anselme Sawadogo <anselmesawadogo@gmail.com>
262 * Author: Olivier Dugeon <olivier.dugeon@orange.com>
263 * Copyright (C) 2016 - 2018 Orange Labs http://www.orange.com
265 This work has been performed in the framework of the H2020-ICT-2014
266 project 5GEx (Grant Agreement no. 671636), which is partially funded
267 by the European Commission.