Hello @carl.townshend,
To control inbound traffic from the internet to your site, you have a few options, including [1]AS path prepending, [2]community tagging, and [3]BGP MED values.
[1]You can prepend your AS path multiple times on the least preferred inbound path. By making the AS path longer on one of the links, you can influence inbound traffic to prefer the other link. However, this method is not always effective as some ISPs may not consider AS path length as the sole criteria for route selection.
[2]If your upstream providers support it, you can use community tags to signal your preferences for inbound traffic. You can ask your providers to honor specific community tags and use them to manipulate route selection. For example, you can tag routes from one provider with a specific community and ask the other provider to prioritize or de-prioritize those routes based on the community tag.
[3]You can use BGP MED values to influence inbound traffic. By assigning lower MED values to routes received from the preferred provider and higher MED values to routes received from the other provider, you can influence inbound traffic to prefer the lower MED routes. However, this method relies on your upstream providers honoring the MED values and may not always be effective.
--Note that the effectiveness of these methods can vary depending on how your upstream providers implement their routing policies. It's recommended to coordinate with your providers to understand their capabilities and discuss the best approach for influencing inbound traffic.
Regarding outbound traffic, using local preference or weight is a common method. You can assign a higher local preference value or weight to the desired outbound route, which will make it more preferred by your BGP router when selecting the best path for outbound traffic. Weight BGP is specific to Cisco devices.
Best regards
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