Hello @Mlex1,
In the context of configuring BGP, the `activate` command is used to activate a BGP neighbor. However, whether you need to use it or not depends on the specific behavior of the router and the configuration.
In your first example:
router bgp 12345
neighbor 192.168.0.1 remote-as 3456
neighbor 192.168.0.1 description TEST
neighbor 192.168.0.2 remote-as 6789
neighbor 192.168.0.2 description TEST1
address-family ipv4
neighbor 192.168.0.1 activate
neighbor 192.168.0.2 activate
You have explicitly used the `activate` command for both BGP neighbors (192.168.0.1 and 192.168.0.2). This means you are explicitly telling the router to activate the BGP session with these neighbors. The `activate` command ensures that the router initiates the BGP session establishment process with these neighbors.
In yor second example:
router bgp 12345
no bgp default ipv4-unicast
neighbor 192.168.0.1 remote-as 3456
neighbor 192.168.0.1 description TEST
neighbor 192.168.0.2 remote-as 6789
neighbor 192.168.0.2 description TEST1
address-family ipv4
neighbor 192.168.0.1 activate
neighbor 192.168.0.2 activate
You have disabled the default IPv4 unicast behavior with `no bgp default ipv4-unicast`, but you still included `neighbor 192.168.0.1 activate` and `neighbor 192.168.0.2 activate`. In this case, these `activate` commands are redundant because, without them, the BGP neighbors would still be activated due to the `neighbor` statements in the configuration.
The use of `activate` can be optional in some BGP configurations. It is typically used when you want to explicitly specify which BGP neighbors to activate, especially in situations where there are many configured neighbors, and you only want to establish BGP sessions with a subset of them. However, if you have the `neighbor` statements in your configuration without `activate`, the router will still attempt to establish BGP sessions with those neighbors.
In Cisco IOS XR, the activate command is not necessary when configuring BGP. Cisco IOS XR uses a different approach to handle the activation of BGP neighbors compared to classic Cisco IOS. In Cisco IOS XR, when you configure a BGP neighbor using the neighbor command, the router automatically considers that neighbor as active by default. You don't need to explicitly use the activate command. This simplifies the BGP configuration process by eliminating the need for the activate command found in classic Cisco IOS.
Best regards
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