|OSPF6D(8)||System Manager's Manual||OSPF6D(8)|
ospf6dis an Open Shortest Path First (OSPF) daemon which manages routing tables. This implementation supports OSPF version 3, thus it is only capable of maintaining IPv6 routing tables.
OSPF is an interior gateway protocol designed to supersede RIP. It has several advantages over RIP. For instance, every router has an understanding of the complete network topology. Response to changes in the network is faster. Furthermore, failure detection is improved.
The OSPF daemon maintains a Link State Database (LSDB) containing information about routers and networks within an Autonomous System (AS).
Dijkstra's shortest path first algorithm is used to compute a Routing Information Base (RIB) using the LSDB as input. The Forwarding Information Base (FIB), a.k.a. the kernel routing table, is updated with information from the RIB.
OSPF routers discover one another automatically via OSPF hello packets. OSPF routers communicate via two multicast groups: ff02::5 (all Shortest Path First routers) and ff02::6 (all Designated Routers). OSPF runs directly on top of IP and uses neither TCP nor UDP. IP protocol number 89 is reserved for OSPF.
All routers in an OSPF network spend most of their time keeping each others' LSDBs in sync. All routers must have the same information in the LSDB at all times. Every time the LSDB is updated the RIB is updated; if needed the FIB is also updated.
In a multi-access network such as Ethernet, it is unfeasible for all routers to synchronize their LSDB with all other routers in the network. In such networks a Designated Router (DR) and a Backup Designated Router (BDR) are elected. The DR's responsibility is to synchronize with all routers; the BDR will not do much until the DR fails. The first router in a network is automatically elected DR, the second router BDR. All routers have a FULL adjacency with the DR and the BDR. Routers with FULL adjacency exchange information about their LSDBs. A router not elected either DR or BDR will have 2-WAY adjacency with all routers but the DR and BDR. Routers with 2-WAY adjacency recognize that they know each other, but do not exchange information about their LSDBs. If a DR or BDR fails another router is elected DR or BDR and all routers form FULL adjacencies with the newly elected DR or BDR.
When routers are connected via point-to-point links, DR and BDR election is skipped since only two routers are connected to the link.
To limit the impact changes in the network have on the LSDB it is possible to segment an OSPF network into areas. Area 0.0.0.0 (a.k.a. the backbone area) must always be present. Routers can be configured as Area Border Router (ABR), being part of multiple areas. Every area must have direct access to the backbone area. ABRs not directly connected to the backbone area need to establish a virtual link to a router in the backbone area.
AS Border Routers (ASBR) are connected to an OSPF network and other external networks via BGP, RIP, or static routing, and provide connectivity to networks outside the AS.
ospf6d is usually started at boot time,
and can be enabled by setting the following in
ospf6d can be controlled with
the ospf6ctl(8) utility.
The options are as follows:
ospf6dwill run in the foreground and log to stderr.
R. Coltun, D. Ferguson, J. Moy, and A. Lindem, OSPF for IPv6, RFC 5340, July 2008.
ospf6dprogram first appeared in OpenBSD 4.2.
Support for multiple areas is currently not available in
Unlike OSPF for IPv4, OSPF for IPv6 has no built-in support for
authentication of OSPF packets. Instead, it relies on IPsec for packet
authentication. Because OSPF uses multicast, IKE cannot be used for
configuring IPsec flows securing OSPF traffic.
ospf6d is currently entirely unaware of IPsec and
has no support for helping users setting up IPsec flows between OSPF
routers. However, setting up IPsec flows between routers using manual keying
is strongly recommended to protect the OSPF network against spoofing
attacks. Note in particular that flows need to be configured for multicast
groups ff02::5 and ff02::6. See
|July 27, 2015||OpenBSD-current|