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Create dynamicrouting_bgp.rst (#293)
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====================
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Dynamic Routing: BGP
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====================
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.. Note::
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Since OPNsense version 20.7 the frr package was updated to version 7,
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which requires an eBGP outbound policy by default. The requirement was
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disabled but it is strongly advised to use a prefix-list and filter
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your networks to your outbound neighbors.
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-------------
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Configuration
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-------------
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The following tables describe the most used configurations.
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General:
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====================== =======================================================================
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Setting Description
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====================== =======================================================================
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Enable Enables the BGP daemon
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BGP AS Number The internal AS number
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Router ID Router ID this system is uses for communication with other peers
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Network A list of local networks to announce. With frr version 6 this setting
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and an additional Null-Route was enough to announce the networks
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Now it is advised to add a prefix-list and link it in neighbor config
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Route Redistribution Allows to redistribute additional routes (static, kernel, OSPF etc.)
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into the BGP process. Usually this is only used with OSPF but also
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available here
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====================== =======================================================================
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Neighbors:
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========================= ===================================================================
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Setting Description
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========================= ===================================================================
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Enable Enables the neighbor config
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Description Give a description for documentation when many neighbors are used
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Peer IP The IP address of the neighbor
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Remote AS Remote AS where this neighbor belongs to. For iBGP this has to be
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the same number as in General tab
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Update-Source Interface Interface name nearest to the peer, usually WAN for eBGP and LAN
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for iBGP
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Next-Hop-Self Enable this option if this is an iBGP neighbor
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Multi-Hop When the neighbor is not directly connected enable this option
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BGP packets usually have a TTL of 1 and would get lost otherwise
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Send Defaultroute Enable this option to send the neighbor itself as default gateway
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Prefix-List Match against linked prefix-list and direction of in and out
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To advertise a network to neighbor it would be direction out
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To filter out specific networks advertised by peer it would be in
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Route-Map Same as prefix-list but used with route-maps. Route-maps are more
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powerful compared to prefix-list but also more complex
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========================= ===================================================================
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AS Path Lists:
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============= ===================================================================
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Setting Description
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============= ===================================================================
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Enable Enables the list entry
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Description Give a description for documentation when many entries are used
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Number The ACL rule number (10-99); keep in mind that there are no
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sequence numbers with AS-Path lists. When you want to add a
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new line between you have to completely remove the ACL
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Action Permit or Deny for this list. This can also be done via route-map
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AS A regular expression to match for AS Paths like *.$*. This is
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typically used for path prepending
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============= ===================================================================
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Prefix Lists:
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================= ===================================================================
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Setting Description
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================= ===================================================================
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Enable Enables the list entry
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Name Prefix Lists are named lists so they are not grouped by a number
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Description Give a description for documentation when many entries are used
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Sequence Number Multiple rules can belong to a named list. With the squence
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number the ordering is done (top to bottom)
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Action Permit or Deny for this list. This can also be done via route-map
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Network The network pattern to match. It is also possible to add "ge" or
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"le" additions after the network statement. Usually this is used
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to announce the local network or maybe to decline specific routes
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from a neighbor
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================= ===================================================================
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Community Lists:
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================= ===================================================================
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Setting Description
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================= ===================================================================
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Enable Enables the list entry
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Number Prefix Lists are numbered lists so they are not grouped by a name
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Description Give a description for documentation when many entries are used
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Sequence Number Multiple rules can belong to a named list. With the squence
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number the ordering is done (top to bottom)
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Action Permit or Deny for this list. This can also be done via route-map
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Community The BGP communities attribute is widely used for implementing
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policy routing. Network operators can manipulate BGP communities
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attribute based on network policy
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================= ===================================================================
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Route Maps:
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============= =================================================================
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Setting Description
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============= =================================================================
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Enable Enables the list entry
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Description Give a description for documentation when many entries are used
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Name Route Maps are named lists so they are not grouped by a number
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Action Permit or Deny for this list
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ID Multiple rules can belong to a route-map. With the ID the
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ordering is done (top to bottom)
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AS Path A linked AS Path to match against
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Prefix List A linked Prefix List to match against
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Community A linked Community List to match against
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Set Via the set statement the specified matches can be manipulated.
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There are many options to set communities, change the local
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preference for gateway selection or use metrics for MED (Multi
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Exit Descriminator)
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============= =================================================================
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Here you can find a couple of examples:
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http://docs.frrouting.org/en/latest/bgp.html#miscellaneous-configuration-examples
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