Added some comments.
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3 changed files with 48 additions and 1 deletions
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@ -97,6 +97,27 @@ ospf_sk_open(struct ospf_iface *ifa)
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goto err;
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#endif
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/*
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* For OSPFv2: When sending a packet, it is important to have a
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* proper source address. We expect that when we send one-hop
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* unicast packets, OS chooses a source address according to the
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* destination address (to be in the same prefix). We also expect
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* that when we send multicast packets, OS uses the source address
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* from sk->saddr registered to OS by sk_setup_multicast(). This
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* behavior is needed to implement multiple virtual ifaces (struct
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* ospf_iface) on one physical iface and is signalized by
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* CONFIG_MC_PROPER_SRC.
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*
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* If this behavior is not available (for example on BSD), we create
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* non-stub iface just for the primary IP address (see
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* ospf_iface_stubby()) and we expect OS to use primary IP address
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* as a source address for both unicast and multicast packets.
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*
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* FIXME: the primary IP address is currently just the
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* lexicographically smallest address on an interface, it should be
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* signalized by sysdep code which one is really the primary.
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*/
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sk->saddr = ifa->addr->ip;
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if (sk_setup_multicast(sk) < 0)
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goto err;
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@ -42,6 +42,32 @@
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* and deletion. Each LSA is kept in two pieces: header and body. Both of them are
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* kept in the endianity of the CPU.
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*
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* In OSPFv2 specification, it is implied that there is one IP prefix
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* for each physical network/interface (unless it is an ptp link). But
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* in modern systems, there might be more independent IP prefixes
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* associated with an interface. To handle this situation, we have
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* one &ospf_iface for each active IP prefix (instead for each active
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* iface); This behaves like virtual interface for the purpose of OSPF.
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* If we receive packet, we associate it with a proper virtual interface
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* mainly according to its source address.
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*
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* OSPF keeps one socket per &ospf_iface. This allows us (compared to
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* one socket approach) to evade problems with a limit of multicast
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* groups per socket and with sending multicast packets to appropriate
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* interface in a portable way. The socket is associated with
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* underlying physical iface and should not receive packets received
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* on other ifaces (unfortunately, this is not true on
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* BSD). Generally, one packet can be received by more sockets (for
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* example, if there are more &ospf_iface on one physical iface),
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* therefore we explicitly filter received packets according to
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* src/dst IP address and received iface.
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*
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* Vlinks are implemented using particularly degenerate form of
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* &ospf_iface, which has several exceptions: it does not have its
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* iface or socket (it copies these from 'parent' &ospf_iface) and it
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* is present in iface list even when down (it is not freed in
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* ospf_iface_down()).
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*
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* The heart beat of ospf is ospf_disp(). It is called at regular intervals
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* (&proto_ospf->tick). It is responsible for aging and flushing of LSAs in
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* the database, for routing table calculaction and it call area_disp() of every
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@ -159,7 +159,7 @@ struct ospf_iface
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{
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node n;
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struct iface *iface; /* Nest's iface */
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struct ifa *addr;
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struct ifa *addr; /* IP prefix associated with that OSPF iface */
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struct ospf_area *oa;
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struct object_lock *lock;
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sock *sk; /* IP socket (for DD ...) */
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