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• AS - Autonomous System
• ASN - Autonomous System Number
• NLRI - Network Layer Reachability Information is what is being exchanged between BGP peers and represents how to reach the prefixes.
• IGP - Interior Gateway Protocol
• EGP - Exterior Gateway protocol
• RR - Route reflector is the router in the BGP network that reflects advertisements to all the neighbors, avoiding the requirement for full BGP mesh. 
• Route server - is the BGP router that does not participate in traffic forwarding. Routes are typically not even installed in the FIB.
• loopback address - a /32 address configured on a dummy bridge interface, that can act as a loopback.

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BGP Basics

BGP routers exchange reachability information by means of a transport protocol, which in the case of BGP is TCP (port 179). Upon forming a TCP connection these routers exchange OPEN messages to negotiate and confirm supported capabilities.

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To respond to errors or special conditions, NOTIFICATION messages can be generated and sent to the remote peer, notification message type also indicates whether the connection should be immediately closed.

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There can be two types of BGP connections:

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For certain BGP attributes handling behavior may change depending on what type of connection is set up, for example, the LOCAL-PREF attribute is not advertised to eBGP peers.

RouterOS divides configuration and session monitoring into three menus:

• connection menu (/routing/bgp/connection)
• sessions menu(/routing/bgp/session)
• template menu (/routing/bgp/template)

Connection Menu

Let's look at a very basic eBGP configuration example assuming, that Router1 IP is 192.168.1.1, AS 65531 and Router2 IP 192.168.1.2, AS 65532:

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BGP connection menu defines BGP outgoing connections as well as acts as a template matcher for incoming BGP connections. We will discuss templating and dynamic peering later in this article.

To see the actual active sessions with selected template parameters and negotiated capabilities refer to the BGP sessions menu:

[admin@MikroTik] /routing/bgp/session> print 
Flags: E - established 
 0 E name="toR2" 
     remote.address=192.168.1.2 .as=65532 .id=192.168.1.1 .refused-cap-opt=no 
     .capabilities=mp,rr,as4 .afi=ip,ipv6 .messages=43346 .bytes=3635916 .eor="" 
     local.address=192.168.1.1 .as=65531 .id=192.168.44.2 .capabilities=mp,rr,gr,as4 .messages=2 
     .bytes=71 .eor="" 
     output.procid=97 .keep-sent-attributes=no 
     .last-notification=ffffffffffffffffffffffffffffffff0015030601 
     input.procid=97 .limit-process-routes=500000 ebgp limit-exceeded 
     hold-time=3m keepalive-time=1m uptime=4s70ms

 local.role parameter is used to indicate that this connection will be the eBGP. Also, notice that the connection does not require a remote AS number to be specified, RouterOS can determine a remote AS number dynamically from the first received OPEN message.

Parameter equivalent to other vendors and older RouterOS "update-source" is "local.address". In most cases, it can be left unconfigured, and let the router determine the address.

When a local address is not specified, BGP will try to guess the local address depending on the current setup:

• if the peer is iBGP
  • if loopback available
    • pick the highest loopback address
  • if loopback is not available
    • pick any highest IP address on the router
• if the peer is eBGP
  • if a remote peer's IP is not from a directly connected network:
    • and multihop is not set, then throw an error
    • and multihop is enabled:
      • if loopback available
        • pick the highest loopback address
      • if loopback is not available
        • pick any highest IP address on the router
  • if a remote peer's IP is from a directly connected network:
    • and multihop is not set:
      • pick the local routers IP address from that connected network
    • and multihop is set:
      • if loopback available
        • pick the highest loopback address
      • if loopback is not available
        • pick any highest IP address on the router

Property Reference

Template

Sub Menu: /routing/bgp/template

The template contains all BGP protocol-related configuration options. It can be used as a template for dynamic peers and to apply a similar configuration to a group of peers. Note that this is not the same as peer groups on Cisco devices, where the group is more than just a common configuration.

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 local.role parameter is used to indicate that this connection will be the eBGP. Also, notice that the connection does not require a remote AS number to be specified, RouterOS can determine a remote AS number dynamically from the first received OPEN message.

Parameter equivalent to other vendors and older RouterOS "update-source" is "local.address". In most cases, it can be left unconfigured, and let the router determine the address.

When a local address is not specified, BGP will try to guess the local address depending on the current setup:

• if the peer is iBGP
  • if loopback available
    • pick the highest loopback address
  • if loopback is not available
    • pick any highest IP address on the router
• if the peer is eBGP
  • if a remote peer's IP is not from a directly connected network:
    • and multihop is not set, then throw an error
    • and multihop is enabled:
      • if loopback available
        • pick the highest loopback address
      • if loopback is not available
        • pick any highest IP address on the router
  • if a remote peer's IP is from a directly connected network:
    • and multihop is not set:
      • pick the local routers IP address from that connected network
    • and multihop is set:
      • if loopback available
        • pick the highest loopback address
      • if loopback is not available
        • pick any highest IP address on the router

In addition to connection-specific parameters, template-specific parameters are also directly exposed in this menu, for easier configuration in simple scenarios (when templates are not necessary).

A list of all connection-specific parameters can be seen in the table below:

Session Menu

To see the actual active sessions with selected template parameters and negotiated capabilities refer to the BGP sessions menu:

[admin@MikroTik] /routing/bgp/session> print 
Flags: E - established 
 0 E name="toR2" 
     remote.address=192.168.1.2 .as=65532 .id=192.168.1.1 .refused-cap-opt=no 
     .capabilities=mp,rr,as4 .afi=ip,ipv6 .messages=43346 .bytes=3635916 .eor="" 
     local.address=192.168.1.1 .as=65531 .id=192.168.44.2 .capabilities=mp,rr,gr,as4 .messages=2 
     .bytes=71 .eor="" 
     output.procid=97 .keep-sent-attributes=no 
     .last-notification=ffffffffffffffffffffffffffffffff0015030601 
     input.procid=97 .limit-process-routes=500000 ebgp limit-exceeded 
     hold-time=3m keepalive-time=1m uptime=4s70ms

This menu shows read-only cached BGP session information. It will show the current status of the session, flags, last received notification, and negotiated session parameters.

Even if the BGP session is not active anymore, the cache can still be stored for some time. Routes received from a particular session are removed only if the cache expires, this allows to mitigate extensive routing table recalculations if the BGP session is flapping.

Also, in this menu is located a session-specific set of commands. 

List of available commands:

Template Menu

The template contains all BGP protocol-related configuration options. It can be used as a template for dynamic peers and to apply a similar configuration to a group of peers. Note that this is not the same as peer groups on Cisco devices, where the group is more than just a common configuration.

List of available template parameters:

Connection

Sub Menu: /routing/bgp/connection

This menu is used to define BGP outgoing connections as well as listen to a single or group of remote BGP peer connections.

In addition to connection-specific parameters, template-specific parameters are also directly exposed in this menu, for easier configuration in simple scenarios (when templates are not necessary).

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Session

Sub Menu: /routing/bgp/session

This menu shows read-only cached BGP session information. It will show the current status of the session, flags, last received notification, and negotiated session parameters.

Even if the BGP session is not active anymore, the cache can still be stored for some time. Routes received from a particular session are removed only if the cache expires, this allows to mitigate extensive routing table recalculations if the BGP session is flapping.

Commands

VPLS

Sub Menu: /routing/bgp/vpls

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