Implementation details
----------------------
+### Concepts
-Segment Routing used 3 differents OPAQUE LSA in OSPF to carry the various information:
- - Router Information: flood the Segment Routing capabilities of the node. This include
- the supported algorithms, the Segment Routing Global Block (SRGB) and the Maximum Stack
- Depth.
+Segment Routing used 3 differents OPAQUE LSA in OSPF to carry the various
+information:
+
+ - Router Information: flood the Segment Routing capabilities of the node.
+ This include the supported algorithms, the Segment Routing Global Block
+ (SRGB) and the Maximum Stack Depth (MSD).
- Extended Link: flood the Adjaceny and Lan Adjacency Segment Identifier
- Extended Prefix: flood the Prefix Segment Identifier
-The implementation follow previous TE and Router Information code. It used the OPAQUE LSA
-functions define in ospf_opaque.[c,h] as well as the OSPF API. This latter is mandatory
-for the implementation as it provides the Callback to Segment Routing functions (see below)
-when an Extended Link / Prefix or Router Information is received.
+The implementation follow previous TE and Router Information code. It used the
+OPAQUE LSA functions define in ospf_opaque.[c,h] as well as the OSPF API. This
+latter is mandatory for the implementation as it provides the Callback to
+Segment Routing functions (see below) when an Extended Link / Prefix or Router
+Information is received.
+
+### Overview
Following files where modified or added:
- ospd_ri.[c,h] have been modified to add the new TLVs for Segment Routing.
- - ospf_ext.[c,h] implement RFC7684 as base support of Extended Link and Prefix Opaque LSA.
- - ospf_sr.[c,h] implement the earth of Segment Routing. It adds a new Segment Routing database
- to manage Segment Identifiers per Link and Prefix and Segment Routing enable node, Callback
- functions to process incoming LSA and install MPLS FIB entry through Zebra.
-
-the figure below shows the relation between the various files:
-
- - ospf_sr.c centralized all the Segment Routing processing. It receives Opaque LSA
- Router Information (4.0.0.0) from ospf_ri.c and Extended Prefix (7.0.0.X) Link (8.0.0.X)
- from ospf_ext.c. Once received, it parse TLVs and SubTLVs and store information in SRDB
- (which is defined in ospf_sr.h). For each received LSA, NHLFE is computed and send to
- Zebra to add/remove new MPLS labels entries and FEC. New CLI configurations are also
- centralized in ospf_sr.c. This CLI will trigger the flooding os new LSA Router Information
- (4.0.0.0), Extended Prefix (7.0.0.X) and Link (8.0.0.X) by ospf_ri.c, respectively ospf_ext.c.
- - ospf_ri.c send back to ospf_sr.c received Router Information LSA and update self Router
- Information LSA with paramters provided by ospf_sr.c i.e. SRGB and MSD. It use ospf_opaque.c
- functions to send / received these Opaque LSAs.
- - ospf_ext.c send bacl to ospf_sr.c received Extended Prefix and Link Opaque LSA and send
- self Extended Prefix and Link Opaque LSA through ospf_opaque.c functions.
+ - ospf_ext.[c,h] implement RFC7684 as base support of Extended Link and Prefix
+ Opaque LSA.
+ - ospf_sr.[c,h] implement the earth of Segment Routing. It adds a new Segment
+ Routing database to manage Segment Identifiers per Link and Prefix and
+ Segment Routing enable node, Callback functions to process incoming LSA and
+ install MPLS FIB entry through Zebra.
+
+The figure below shows the relation between the various files:
+
+ - ospf_sr.c centralized all the Segment Routing processing. It receives Opaque
+ LSA Router Information (4.0.0.0) from ospf_ri.c and Extended Prefix
+ (7.0.0.X) Link (8.0.0.X) from ospf_ext.c. Once received, it parse TLVs and
+ SubTLVs and store information in SRDB (which is defined in ospf_sr.h). For
+ each received LSA, NHLFE is computed and send to Zebra to add/remove new
+ MPLS labels entries and FEC. New CLI configurations are also centralized in
+ ospf_sr.c. This CLI will trigger the flooding of new LSA Router Information
+ (4.0.0.0), Extended Prefix (7.0.0.X) and Link (8.0.0.X) by ospf_ri.c,
+ respectively ospf_ext.c.
+ - ospf_ri.c send back to ospf_sr.c received Router Information LSA and update
+ Self Router Information LSA with paramters provided by ospf_sr.c i.e. SRGB
+ and MSD. It use ospf_opaque.c functions to send/received these Opaque LSAs.
+ - ospf_ext.c send back to ospf_sr.c received Extended Prefix and Link Opaque
+ LSA and send self Extended Prefix and Link Opaque LSA through ospf_opaque.c
+ functions.
+
+::
+-----------+ +-------+
| | | |
| |
+---------------+
+ Figure1: Overview of Segment Routing interaction
+
+### Module interactions
+
+To process incoming LSA, the code is based on the capability to call `hook()` functions when LSA are inserted or delete to / from the LSDB and the possibility to register particular treatment for Opaque LSA. The first point is provided by the OSPF API feature and the second by the Opaque implementation itself. Indeed, it is possible to register callback function for a given Opaque LSA ID (see `ospf_register_opaque_functab()` function defined in `ospf_opaque.c`). Each time a new LSA is added to the LSDB, the `new_lsa_hook()` function previously register for this LSA type is called. For Opaque LSA it is the `ospf_opaque_lsa_install_hook()`. For deletion, it is `ospf_opaque_lsa_delete_hook()`.
+
+Note that incoming LSA which is already present in the LSDB will be inserted after the old instance of this LSA remove from the LSDB. Thus, after the first time, each incoming LSA will trigger a `delete` following by an `install`. This is not very helpfull to handle real LSA deletion. In fact, LSA deletion is done by Flushing LSA i.e. flood LSA after seting its age to MAX_AGE. Then, a garbage function has the role to remove all LSA with `age == MAX_AGE` in the LSDB. So, to handle LSA Flush, the best is to look to the LSA age to determine if it is an installation or a future deletion i.e. the flushed LSA is first store in the LSDB with MAX_AGE waiting for the garbage collector function.
+
+#### Router Information LSAs
+
+To activate Segment Routing, new CLI command `segment-routing on` has been introduced. When this command is activated, function `ospf_router_info_update_sr()` is called to indicate to Router Information process that Segment Routing TLVs must be flood. Same function is called to modify the Segment Routing Global Block (SRGB) and Maximum Stack Depth (MSD) TLV. Only Shortest Path First (SPF) Algorithm is supported, so no possiblity to modify this TLV is offer by the code.
+
+When Opaque LSA Tyep 4 i.e. Router Information are stored in LSDB, function `ospf_opaque_lsa_install_hook()` will call the previously registered function `ospf_router_info_lsa_update()`. In turn, the function will simply trigger `ospf_sr_ri_lsa_update()` or `ospf_sr_ri_lsa_delete` in function of the LSA age. Before, it verifies that the LSA Opaque Type is 4 (Router Information). Self Opaque LSA are not send back to the Segment Routing functions as information are already stored.
+
+#### Extended Link Prefix LSAs
+
+Like for Router Information, Segment Routing is activate at the Extended Link/Prefix level with new `segment-routing on` command. This trigger automtically the flooding of Extended Link LSA for all ospf interface where adjacency is full. For Extended Prefix LSA, the new CLI command `segment-routing prefix ...` will trigger the flooding of Prefix SID TLV/SubTLVs.
+
+When Opaque LSA Type 7 i.e. Extended Prefix and Type 8 i.e. Extended Link are store in the LSDB, `ospf_ext_pref_update_lsa()` respectively `ospf_ext_link_update_lsa()` are called like for Router Information LSA. In turn, they respectively trigger `ospf_sr_ext_prefix_lsa_update()` / `ospf_sr_ext_link_lsa_update()` or `ospf_sr_ext_prefix_lsa_delete()` / `ospf_sr_ext_link_lsa_delete()` if the LSA age is equel to MAX_AGE.
+
+#### Zebra
+
+When a new MPLS entry of new Forwarding Equivalent Class (FEC) must be add or delete in the data plane, `add_sid_nhlfe()` respectively `del_sid_nhlfe()` are called. Once check the validity of labels, they send to ZEBRA layer a new labels through `ZEBRA_MPLS_LABELS_ADD` command, respectively `ZEBRA_MPLS_LABELS_DELETE` command for deletion. This is completed by a new labelled route through `ZEBRA_ROUTE_ADD` command, respectively `ZEBRA_ROUTE_DELETE` command.
+
+Configuration
+-------------
+
+Here it is a simple example of configuration to enable Segment Routing. Note
+that ``opaque capability`` must be set to activate Opaque LSA prior to Segment
+Routing.
+
+::
+
+ router ospf
+ ospf router-id 192.168.1.11
+ capability opaque
+ mpls-te on
+ mpls-te router-address 192.168.1.11
+ router-info area 0.0.0.0
+ segment-routing on
+ segment-routing global-block 10000 19999
+ segment-routing node-msd 8
+ segment-routing prefix 192.168.1.11/32 index 1100
+
+The first segment-routing statement enable it. The Second one set the SRGB,
+third line the MSD and finally, set the Prefix SID index for tha given prefix.
+Note that only prefix of Loopback interface could be configured with a Prefix
+SID.
Known limitations
-----------------
+ - Runs only within default VRF
- Only single Area is supported. ABR is not yet supported
- Only SPF algorithm is supported
- Extended Prefix Range is not supported
+ - MPLS table are not flush at startup. Thus, restarting zebra process is mandatory to remove old MPLS entries in the data plane after a crash of ospfd daemon.
+
+Credits
+-------
+ * Author: Anselme Sawadogo <anselmesawadogo@gmail.com>
+ * Author: Olivier Dugeon <olivier.dugeon@orange.com>
+ * Copyright (C) 2016 - 2018 Orange Labs http://www.orange.com
+
+This work has been performed in the framework of the H2020-ICT-2014
+project 5GEx (Grant Agreement no. 671636), which is partially funded
+by the European Commission.
+
projects / mirror_frr.git / blobdiff