1BGPD(8) BSD System Manager's Manual BGPD(8)
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4 bgpd — Border Gateway Protocol daemon
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7 bgpd [-cdnv] [-D macro=value] [-f file]
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10 bgpd is a Border Gateway Protocol (BGP) daemon which manages the network
11 routing tables. Its main purpose is to exchange information concerning
12 "network reachability" with other BGP systems. bgpd uses the Border
13 Gateway Protocol, Version 4, as described in RFC 4271.
14 BGP is an exterior gateway protocol using a multiple step decision
16 process to find the best path. Advanced filtering can be used to influ‐
17 ence the route decision for traffic engineering. The session engine of
18 bgpd is responsible for maintaining the TCP session with each neighbor.
19 Updates are passed to the Route Decision Engine (RDE) where the paths are
20 filtered and used to compute a Routing Information Base (RIB). The par‐
21 ent process is responsible for keeping the RIB in sync with the kernel
22 routing table.
23 The route decision process selects the best path by evaluating all paths
25 to the same destination. The decision process continues to the next step
26 if paths have equal attributes. Paths that are less preferred are taken
27 out of consideration until there is only one path left.
28 1. All paths with errors or loops are not eligible.
30 2. Paths with an unreachable nexthop are not eligible. After this
32 step all remaining paths are valid.
33 3. The path with the highest LOCAL_PREF is selected.
35 4. The path with the shortest AS path attribute is selected.
37 5. The ORIGIN attribute is compared. The order is IGP before EGP
39 before incomplete origins.
40 6. The path with the lowest MULTI_EXIT_DISC metric is selected.
42 Normally, this value is only considered when choosing between
43 multiple routes sent by the same neighbouring AS. However, if
44 “rde med compare always” is set in the configuration, the metric
45 is compared for routes sent by any AS.
46 7. Comparison of the BGP session type. Paths learned over an exter‐
48 nal (EBGP) session are preferred over those learned via an inter‐
49 nal (IBGP) session.
50 8. The path with the highest local weight is selected.
52 9. If “rde route-age evaluate” is set then the oldest path is se‐
54 lected.
55 10. The path coming from the neighbor with the lowest BGP ID wins.
57 If the ORIGINATOR_ID attribute is present that value will be used
58 in the comparison instead.
59 11. The path with the shortest CLUSTER_LIST attribute is selected.
61 If it is not present then a length of 0 is used in the compari‐
62 son.
63 12. The path coming from the peer with the lowest IP address is se‐
65 lected. IPv4 sessions will be preferred over IPv6 ones.
66 Attributes set by filters can be used to tip the decision process to pre‐
68 fer particular paths over others. This can be achieved by changing the
69 localpref, med, or weight attributes. AS path prepending or changing the
70 med or origin attribute can be used to influence the routing behaviour on
71 remote systems.
72 To have bgpd enabled at boot time, use “rcctl enable bgpd”, which sets
74 bgpd_flags=""
76 in rc.conf.local(8).
78 When bgpd starts up, it reads settings from a configuration file, typi‐
80 cally bgpd.conf(5). A running bgpd process can be controlled using the
81 bgpctl(8) utility.
82 The options are as follows:
84 -c Force bgpd to do carp(4) demotion at startup when the demote
86 functionality is used. Normally, bgpd will only do demotion
87 at startup when the demotion counter for the group in ques‐
88 tion is already greater than 0. bgpd will start handling de‐
89 motion after all sessions with demotion configured for the
90 given group have been successfully established. At system
91 startup, rc(8) has the demotion counter for the group carp
92 increased until after bgpd is started, so this option should
93 not be used in rc.conf(8).
94 -D macro=value
96 Define macro to be set to value on the command line. Over‐
97 rides the definition of macro in the configuration file.
98 -d Do not daemonize. If this option is specified, bgpd will run
100 in the foreground and log to stderr.
101 -f file Use file as the configuration file, instead of the default
103 /etc/bgpd.conf.
104 -n Configtest mode. Only check the configuration file for va‐
106 lidity.
107 -v Produce more verbose output.
109
111 /etc/bgpd.conf Default bgpd configuration file.
112 /run/bgpd/bgpd.sock.<rdomain> Default bgpd control socket, where
113 <rdomain> is the routing domain in which
114 bgpd has been started.
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117 bgpd.conf(5), bgpctl(8), bgplg(8), bgplgsh(8)
118
120 R. Chandra, P. Traina, and T. Li, BGP Communities Attribute, RFC 1997,
121 August 1996.
122 A. Heffernan, Protection of BGP Sessions via the TCP MD5 Signature
124 Option, RFC 2385, August 1998.
125 P. Marques and F. Dupont, Use of BGP-4 Multiprotocol Extensions for IPv6
127 Inter-Domain Routing, RFC 2545, March 1999.
128 E. Chen, Route Refresh Capability for BGP-4, RFC 2918, September 2000.
130 G. Huston, NOPEER Community for Border Gateway Protocol (BGP) Route Scope
132 Control, RFC 3765, April 2004.
133 Y. Rekhter, T. Li, and S. Hares, A Border Gateway Protocol 4 (BGP-4), RFC
135 4271, January 2006.
136 S. Sangli, D. Tappan, and Y. Rekhter, BGP Extended Communities Attribute,
138 RFC 4360, February 2006.
139 E. Rosen and Y. Rekhter, BGP/MPLS IP Virtual Private Networks (VPNs), RFC
141 4364, February 2006.
142 T. Bates, E. Chen, and R. Chandra, BGP Route Reflection: An Alternative
144 to Full Mesh Internal BGP (IBGP), RFC 4456, April 2006.
145 E. Chen and V. Gillet, Subcodes for BGP Cease Notification Message, RFC
147 4486, April 2006.
148 T. Bates, R. Chandra, D. Katz, and Y. Rekhter, Multiprotocol Extensions
150 for BGP-4, RFC 4760, January 2007.
151 Q. Vohra and E. Chen, BGP Support for Four-octet AS Number Space, RFC
153 4893, May 2007.
154 V. Gill, J. Heasley, D. Meyer, P. Savola, and C. Pignatoro, The
156 Generalized TTL Security Mechanism (GTSM), RFC 5082, October 2007.
157 J. Scudder and R. Chandra, Capabilities Advertisement with BGP-4, RFC
159 5492, February 2009.
160 E. Chen, J. Scudder, P. Mohapatra, and K. Patel, Revised Error Handling
162 for BGP UPDATE Messages, RFC 7606, August 2015.
163 L. Blunk, M. Karir, and C. Labovitz, Multi-Threaded Routing Toolkit (MRT)
165 Routing Information Export Format, RFC 6396, October 2011.
166 J. Dong, M. Chen, and A. Suryanarayana, Subcodes for BGP Finite State
168 Machine Error, RFC 6608, May 2012.
169 W. Kumari, R. Bush, H. Schiller, and K. Patel, Codification of AS 0
171 Processing, RFC 7607, August 2015.
172 J. Heitz, J. Snijders, K. Patel, I. Bagdonas, and N. Hilliard, BGP Large
174 Communities Attribute, RFC 8092, February 2017.
175 P. Mohapatra, K. Patel, J. Scudder, D. Ward, and R. Bush, BGP Prefix
177 Origin Validation State Extended Community, RFC 8097, March 2017.
178 J. Snijders, J. Heitz, and J. Scudder, BGP Administrative Shutdown
180 Communication, RFC 8203, July 2017.
181 R. Bush and R. Austein, The Resource Public Key Infrastructure (RPKI) to
183 Router Protocol, Version 1, RFC 8210, September 2017.
184 J. Mauch, J. Snijders, and G. Hankins, Default External BGP (EBGP) Route
186 Propagation Behavior without Policies, RFC 8212, July 2017.
187 P. Francois, B. Decraene, C. Pelsser, K. Patel, and C. Filsfils, Graceful
189 BGP Session Shutdown, RFC 8326, March 2018.
190
192 The bgpd program first appeared in OpenBSD 3.5.
193BSD April 8, 2021 BSD