Understood. As it is now, there is no way to mark incoming traffic from 1.1.1.0/24 that came via R1 so that the response to that traffic is sent back to R1 and not to the primary R2. Because the same destination of 1.1.1.0/24 is advertised by both R1 and R2, with the prepend as it is, it can only be sent via R2. Even if you had R1 and R2 in different ASes, you would still find it difficult to resolve the asymmetric routing problem.
What you are trying to achieve is data center redundancy that allows the use of the same prefix of 1.1.1.0/24 behind both data centers. BGP is not ideal for achieving this, especially since it is quite slow in convergence, and because of the problem you have perceived with asymmetric routing.
The problem should be approached in a completely different manner. Specifically, Cisco has some exceptional documentation on how to achieve this, and one of these can be found below:
I know that this is probably not the answer you were looking for, but as far as I can see, using BGP for this purpose is not reasonably achievable.
Yes ISP will provide two links and assign them to the VSI interface , so basically they have layer 3 Vlan interface and assign 2 physical interfaces to the Vlan. No need for additional switch in between.
One other thing you mentioned about the single homed model: BGP is needed regardless of default route. Otherwise none of your public IPs will be advertised so Internet will not be accessible. If we are talking about a home network connecting to an ISP or an enterprise with private IP addresses Natted to ISP public IP then yes BGP is not needed, but if it is an enterprise with public IPs BGP is required to advertise the enterprise routesā¦just wanted to clarify
If the ISP is able to deliver what is needed in order to avoid having the intermediate switch(s) installed, then yes, that would be even better. It all has to do with the negotiation with the ISP, seeing if they can offer you what you need for your edge network to deliver the required level of redundancy.
Yes, absolutely. BGP is only strictly needed when an enterprise has some public IP addresses that are used by internet-facing services such as web servers, email servers, etcā¦ In such cases, BGP must be used to advertise those addresses to the ISP and beyond into the Internet. If itās just a home network or a small business that doesnāt have any such on-site services, then BGP is not needed.
Learning about BGP Attributes, wichone would you use to send the same prefixes (routes) to two ISPs? AS-PATH PREPEND?
I know if youāre using Dual-Homed probably you can use communities an local preferences.
I mean, the ISP can have configured some local preferences that it will match to some communities values, right?
If you are dual-homed, you want to inform both ISPs about your prefixes using BGP. What attributes you will use depends on what you want to achieve.
Typically, the most important thing in such a scenario is how to influence incoming traffic. After all, you are advertising your own routes using BGP in order to tell the rest of the world how to reach your addresses. Influencing incoming traffic can be done using specific attributes, which are described in more detail in this NetworkLessons note.
One thing to keep in mind is that you should always negotiate with each ISP as to how you want your prefixes advertised. Trying to influence incoming traffic by changing attributes can be viewed by the ISP as a āhostileā action or at least an inappropriate action, if you havenāt confirmed with them beforehand. In any event, the ISP can override most attributes you may add to your prefixes, so open negotiation is always the way to go in such cases.
