Also includes minor cleanup of help.

Current FreeBSD kernels require SA records for both directions.

Thanks to Joseph Mulloy and Andrey V. Elsukov for reporting and
solving the issue.

Minor cleanups, updates and clarifications. Also removes (incomplete
and well-known) build steps from README, as they are better described
in INSTALL.

Since v2 we have multiple listening BGP sockets, and each BGP protocol
has associated one of them. Use listening socket that accepted the
incoming connection as a key in the dispatch process so only BGP
protocols assocaited with that listening socket can be selected.
This is necesary for proper dispatch when VRFs are used.

It may happen that the LLv6 address for given iface is not defined during
BGP start, so we postpone the check to the the session establishment.

FreeBSD silently changes TTL to 1 when MSG_DONTROUTE is used, even when
it is explicitly set to another value. That breaks TTL security sockets,
including BFD which always uses TTL 255. Bad FreeBSD!

This protocol is highly experimental and nobody should use it in
production. Anyway it may help you getting some insight into what eats
so much time in filter processing.

In some circumstances (old LSA flushed but not acknowledged and not
removed) origination of a new LSA may wrongly triggers LSA collision
code. The patch fixes that.

Thanks to Asbjorn Mikkelsen for the bugreport and @mdelagueronniere
for the original patch.

Extend 'next hop keep' and 'next hop self' options to have boolean values
(enabled / disabled) and also values 'ibgp'/ 'ebgp' to restrict it to
routes received from IBGP / EBGP. This allows to have it enabled by
default in some cases, matches features of other implementations, and
allows to handle some strange cases like EBGP border router with 'next
hop self' also doing IBGP route reflecting.

Change default of 'next hop keep' to enabled for route servers, and
'ibgp' for route reflectors.

Update documentation for these options.

Flag field was not copied when next hop was cached.

The patch d506263d... blocked adding channel during reconfiguration,
that broke protocols which use the same functiona also during init.
This patch fixes that.

It reduces clutter in root and also avoid collision with doc dir on
case-insensitive filesystems when name back to Doc.

When route is exported to regular EBGP, local ASN should be prepended to
AS_PATH. When route is propagated by route server (between RS-marked
EBGP peers), it should not change AS_PATH. Question is what to do in
other cases (from non-RS EBGP, IBGP, or locally originated to RS EBGP).

In 1.6.x, we did not prepend ASN in non-RS EBGP or IBGP to RS EBGP, but
we prepended in local to RS EBGP.

In 2.0.x, we changed that so only RS-EBGP to RS-EBGP is not prepended.
We received some negative responses (thanks to heisenbug and Alexander
Zubkov), we decided to change it back. One reason is that it is simple
to modify the AS_PATH by filters, but not possible to un-modify
changes done by BGP itself. Also, as 1.6.x behavior was not really
consistent, the final behavior is that ASN is never prepended when
exported to RS EBGP, like to IBGP.

Note that i do not express an opinion about whether such configurations
are even reasonable.

Progdoc comments do not allow SGML tags

The patch implements optional internal import table to a channel and
hooks it to BGP so it can be used as Adj-RIB-In. When enabled, all
received (pre-filtered) routes are stored there and import filters can
be re-evaluated without explicit route refresh. An import table can be
examined using e.g. 'show route import table bgp1.ipv4'.

When a new channel is found during reconfiguration, do force restart
of the protocol, like with any other un-reconfigurable change.

The old behavior was that the new channel was added but remained in down
state, even if the protocol was up, so a manual protocol restart was
often necessary.

In the future this should be improved such that a reconfigurable
channel addition (e.g. direct) is accepted and channel is started,
while an un-reconfigurable addition forces protocol restart.

Fix crash during reconfiguration of OSPF config with vlinks. When vlink
is reconfigured, a generic iface-reconfiguration code is used, which in
one place supposes that it is running on a regular iface.

Thanks to Cybertinus for a bugreport.

For local route marking purposes, local custom route attributes may be
defined. These attributes are seamlessly stripped after export filter to
every real protocol like Kernel, BGP or OSPF, they however pass through
pipes. We currently allow at most 256 custom attributes.

This should be much faster than currently used bgp communities
for marking routes.

Robert Scheck authored 6 years ago and Ondřej Zajíček committed 6 years ago

The existing paths are valid for Debian, alternative paths are necessary
for Fedora and RHEL/CentOS.

The old behavior was that enabling debugging did many nontrivial changes
in BIRD behavior. The patch changes it that these changes are generally
independent. Compiling with --enable-debug now just enables compile-time
debug macros, but do not automatically activate debug mode (-d) nor local
mode (-l). Debug mode with output to file (-D) do not force foreground
mode (-f), therefore there is no need for backgroud option (-b), which is
removed. Also fixes a bug when the default log target in -D mode was
stderr instead of given debug file.

This is still OK for everybody to fit into RAM and also probably enough
to keep a little collision rate for full BGP table.

Once upon a time, far far away, there were the old Bird developers
discussing what direction of route flow shall be called import and
export. They decided to say "import to protocol" and "export to table"
when speaking about a protocol. When speaking about a table, they
spoke about "importing to table" and "exporting to protocol".

The latter terminology was adopted in configuration, then also the
bird CLI in commit ea2ae6dd started to use it (in year 2009). Now
it's 2018 and the terminology is the latter. Import is from protocol to
table, export is from table to protocol. Anyway, there was still an
import_control hook which executed right before route export.

One thing is funny. There are two commits in April 1999 with just two
minutes between them. The older announces the final settlement
on config terminology, the newer uses the other definition. Let's see
their commit messages as the git-log tool shows them (the newer first):

    commit 9e0e485e
    Author: Martin Mares <mj@ucw.cz>
    Date:   Mon Apr 5 20:17:59 1999 +0000

	Added some new protocol hooks (look at the comments for better explanation):

		make_tmp_attrs          Convert inline attributes to ea_list
		store_tmp_attrs         Convert ea_list to inline attributes
		import_control          Pre-import decisions

    commit 5056c559
    Author: Martin Mares <mj@ucw.cz>
    Date:   Mon Apr 5 20:15:31 1999 +0000

	Changed syntax of attaching filters to protocols to hopefully the final
	version:

		EXPORT <filter-spec>    for outbound routes (i.e., those announced
					by BIRD to the rest of the world).
		IMPORT <filter-spec>    for inbound routes (i.e., those imported
					by BIRD from the rest of the world).

	where <filter-spec> is one of:

		ALL                     pass all routes
		NONE                    drop all routes
		FILTER <name>           use named filter
		FILTER { <filter> }     use explicitly defined filter

	For all protocols, the default is IMPORT ALL, EXPORT NONE. This includes
	the kernel protocol, so that you need to add EXPORT ALL to get the previous
	configuration of kernel syncer (as usually, see doc/bird.conf.example for
	a bird.conf example :)).

Let's say RIP to this almost 19-years-old inconsistency. For now, if you
import a route, it is always from protocol to table. If you export a
route, it is always from table to protocol.

And they lived happily ever after.

Modify protocols to use preferred address change notification instead on
depending on hard-reset of interfaces in that case, and remove hard-reset
in that case. This avoids issue when e.g. IPv6 protocol restarts
interface when IPv4 preferred address changed (as hard-reset is
unavoidable and common for whole iface).

The patch also fixes a bug when removing last address does not send
preferred address change notification.

The new MRT protocol is responsible for periodic RIB table dumps in the
MRT format (RFC 6396). Also the existing code for BGP4MP MRT dumps is
refactored and splitted between BGP to MRT protocols, will be more
integrated into MRT in the future.

Example:

protocol mrt {
        table "*";
        filename "%N_%F_%T.mrt";
        period 60;
}

It is partially based on the old MRT code from Pavel Tvrdik.

Allow to specify log file size limit and ensure that log file is rotated
to secondary name to avoid exceeding of log size limit.

The patch also fixes a bug related to keeping old fds open after
reconfiguration and using old fds after 'configure undo'.