bgpd: Fix route install upon multipath nexthop change

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@node SNMP Support
@chapter SNMP Support

@acronym{SNMP,Simple Network Managing Protocol} is a widely implemented
feature for collecting network information from router and/or host.
Quagga itself does not support SNMP agent (server daemon) functionality
but is able to connect to a SNMP agent using the SMUX protocol
(@cite{RFC1227}) or the AgentX protocol (@cite{RFC2741}) and make the
routing protocol MIBs available through it.

@menu
* Getting and installing an SNMP agent::
* AgentX configuration::
* SMUX configuration::
* MIB and command reference::
* Handling SNMP Traps::
@end menu

@node Getting and installing an SNMP agent
@section Getting and installing an SNMP agent

There are several SNMP agent which support SMUX or AgentX. We recommend to use the latest
version of @code{net-snmp} which was formerly known as @code{ucd-snmp}.
It is free and open software and available at @uref{http://www.net-snmp.org/}
and as binary package for most Linux distributions.
@code{net-snmp} has to be compiled with @code{--with-mib-modules=agentx} to
be able to accept connections from Quagga using AgentX protocol or with
@code{--with-mib-modules=smux} to use SMUX protocol.

Nowadays, SMUX is a legacy protocol. The AgentX protocol should be
preferred for any new deployment. Both protocols have the same coverage.

@node AgentX configuration
@section AgentX configuration

To enable AgentX protocol support, Quagga must have been build with the
@code{--enable-snmp} or @code{--enable-snmp=agentx} option. Both the
master SNMP agent (snmpd) and each of the Quagga daemons must be
configured. In @code{/etc/snmp/snmpd.conf}, @code{master agentx}
directive should be added. In each of the Quagga daemons, @code{agentx}
command will enable AgentX support.

@example
/etc/snmp/snmpd.conf:
	#
	# example access restrictions setup
	#
	com2sec readonly default public
	group MyROGroup v1 readonly
	view all included .1 80
	access MyROGroup "" any noauth exact all none none
	#
	# enable master agent for AgentX subagents
	#
	master agentx

/etc/quagga/ospfd.conf:
	! ... the rest of ospfd.conf has been omitted for clarity ...
	!
	agentx
	!
@end example

Upon successful connection, you should get something like this in the
log of each Quagga daemons:

@example
2012/05/25 11:39:08 ZEBRA: snmp[info]: NET-SNMP version 5.4.3 AgentX subagent connected
@end example

Then, you can use the following command to check everything works as expected:

@example
# snmpwalk -c public -v1 localhost .1.3.6.1.2.1.14.1.1
OSPF-MIB::ospfRouterId.0 = IpAddress: 192.168.42.109
[...]
@end example

The AgentX protocol can be transported over a Unix socket or using TCP
or UDP. It usually defaults to a Unix socket and depends on how NetSNMP
was built. If need to configure Quagga to use another transport, you can
configure it through @code{/etc/snmp/quagga.conf}:

@example
/etc/snmp/quagga.conf:
	[snmpd]
	# Use a remote master agent
	agentXSocket tcp:192.168.15.12:705
@end example

@node SMUX configuration
@section SMUX configuration

To enable SMUX protocol support, Quagga must have been build with the
@code{--enable-snmp=smux} option.

A separate connection has then to be established between the
SNMP agent (snmpd) and each of the Quagga daemons. This connections
each use different OID numbers and passwords. Be aware that this OID
number is not the one that is used in queries by clients, it is solely
used for the intercommunication of the daemons.

In the following example the ospfd daemon will be connected to the
snmpd daemon using the password "quagga_ospfd". For testing it is
recommending to take exactly the below snmpd.conf as wrong access
restrictions can be hard to debug.

@example
/etc/snmp/snmpd.conf:
	#
	# example access restrictions setup
	#
	com2sec readonly default public
	group MyROGroup v1 readonly
	view all included .1 80
	access MyROGroup "" any noauth exact all none none
	#
	# the following line is relevant for Quagga
	#
	smuxpeer .1.3.6.1.4.1.3317.1.2.5 quagga_ospfd

/etc/quagga/ospf:
	! ... the rest of ospfd.conf has been omitted for clarity ...
	!
	smux peer .1.3.6.1.4.1.3317.1.2.5 quagga_ospfd
	!
@end example

After restarting snmpd and quagga, a successful connection can be verified in
the syslog and by querying the SNMP daemon:

@example
snmpd[12300]: [smux_accept] accepted fd 12 from 127.0.0.1:36255 
snmpd[12300]: accepted smux peer: \
	oid GNOME-PRODUCT-ZEBRA-MIB::ospfd, quagga-0.96.5

# snmpwalk -c public -v1 localhost .1.3.6.1.2.1.14.1.1
OSPF-MIB::ospfRouterId.0 = IpAddress: 192.168.42.109
@end example

Be warned that the current version (5.1.1) of the Net-SNMP daemon writes a line
for every SNMP connect to the syslog which can lead to enormous log file sizes.
If that is a problem you should consider to patch snmpd and comment out the
troublesome @code{snmp_log()} line in the function
@code{netsnmp_agent_check_packet()} in @code{agent/snmp_agent.c}.

@node MIB and command reference
@section MIB and command reference

The following OID numbers are used for the interprocess communication of snmpd and
the Quagga daemons with SMUX only.
@example
            (OIDs below .iso.org.dod.internet.private.enterprises)
zebra	.1.3.6.1.4.1.3317.1.2.1 .gnome.gnomeProducts.zebra.zserv
bgpd	.1.3.6.1.4.1.3317.1.2.2 .gnome.gnomeProducts.zebra.bgpd
ripd	.1.3.6.1.4.1.3317.1.2.3 .gnome.gnomeProducts.zebra.ripd
ospfd	.1.3.6.1.4.1.3317.1.2.5 .gnome.gnomeProducts.zebra.ospfd
ospf6d	.1.3.6.1.4.1.3317.1.2.6 .gnome.gnomeProducts.zebra.ospf6d
@end example

Sadly, SNMP has not been implemented in all daemons yet. The following
OID numbers are used for querying the SNMP daemon by a client:
@example
zebra	.1.3.6.1.2.1.4.24   .iso.org.dot.internet.mgmt.mib-2.ip.ipForward
ospfd	.1.3.6.1.2.1.14	    .iso.org.dot.internet.mgmt.mib-2.ospf
bgpd	.1.3.6.1.2.1.15	    .iso.org.dot.internet.mgmt.mib-2.bgp 
ripd	.1.3.6.1.2.1.23	    .iso.org.dot.internet.mgmt.mib-2.rip2
ospf6d	.1.3.6.1.3.102	    .iso.org.dod.internet.experimental.ospfv3
@end example

The following syntax is understood by the Quagga daemons for configuring SNMP using SMUX:
@deffn {Command} {smux peer @var{oid}} {}
@deffnx {Command} {no smux peer @var{oid}} {}
@end deffn

@deffn {Command} {smux peer @var{oid} @var{password}} {}
@deffnx {Command} {no smux peer @var{oid} @var{password}} {}
@end deffn

Here is the syntax for using AgentX:
@deffn {Command} {agentx} {}
@deffnx {Command} {no agentx} {}
@end deffn

@include snmptrap.texi