AWS IPSEC on BGP routing (how to control traffic preference for each tunnel?)

[FortDoog]

Good day guys.

I have the following setup.

• 200F with dual WAN
• 4 tunnels to AWS (the usual IPSEC with 2 tunnels).
• Probably, next year, hopefully, I will have AWS Direct Connect.

Let´s begin with the IPSEC tunnels first:

I´m having issues with the ECMP on the AWS TGW, what I need is just failover between the tunnels, but I want to setup the priority in which they are used under normal conditions, like in the following graph:

I want to influence the traffic (inbound and outbound) so it has the Tunnels in this order of preference:

1. Main_Tunnel01
2. Main_Tunnel02
3. Secondary_Tunnel01
4. Secondary_Tunnel02

Or

1. Main IPSEC
2. Secondary IPSEC

Right now, what I´m having (with ECMP disabled) is that I´m loosing traffic partially if I lose a Tunnel. If I enable ECMP, I get traffic through all the tunnels, and I do not want that.

I found the Technical Tip : Difference between asymmetric routing and auxiliary sessions., I will testing that also, but right now I´m confussed with this AWS documentation: 

• https://aws.amazon.com/blogs/networking-and-content-delivery/creating-active-passive-bgp-connections....
• https://repost.aws/knowledge-center/direct-connect-asymmetric-routing
• https://repost.aws/knowledge-center/direct-connect-bgp-communities

IF I understood correctly the AWS docs, I should use:

• Outbound traffic: Local Preference, if not, then I should use AS_Path
• Inbound traffic: Local Preference, if not, MED, if not, then I should use AS_Path

Meaning that I would need two sets of route maps (right?) they would identical in prefix list (my case), but they will differ regarding the Local Preference, MED and AS_Path.

My questions are:

• do I need to setup Local Preference, MED and AS_Path for AWS IPSEC routing inffluencing (all of them, meaning more route maps)?
• or can I use just one of them? meaning, just two route maps, one with more influence than the other,
• if so, which one should I use (Local Preference, MED or AS_Path)???

Keep in mind that I have to leave the space for the future implementation of the Direct Connect, so, whatever I use, I have to leave it so that in case that the Direct Connect fails, the failover SHOULD be Main IPSEC, if the Main IPSEC fails too, then Secondary IPSEC.

Please, I need guidance, oh Wise People of the Community, Help. (FWI: english is my second language, that´s why I´m getting a little confused, sorry about that).

[BillH_FTNT]

Hi FortDoog,
I think what you planned to do with BGP prefixes was right. However, to work with the prefix list, I believe you should change it slightly.
I think the common rule for prefix-list is "len <GE <=LE"
In your case the prefix you configured a.b.c.d 255.224.0.0 ==> the len is 8+7 =15 (225 use 8 bits, 224 use 7 bits)
==> It should be "ge 15"
1. you can do "ge 15" only.
2. or ge 15 le 25
(In your first case, ge 11 is an invalid one, I think)
HTH
Bill

[FortDoog]

any news? anyone?

[BillH_FTNT]

Sorry, I will answer you in next some hours. Quite busy now. Thanks

RG/Bill

[FortDoog]

I can wait, no problem.

[Toshi_Esumi]

I'm not sure if I understand your requirement. But the prefix-list matches what you specify and let matched ones come in (or go out) and take them into BGP table (or send them to neighbors) "as is". It wouldn't summarize to /16 when a /27 matches the prefix-list and place the /16 into the local BGP table.

If you, instead, want to summarize routes when the FGT advertise, like multile /24s into one /16, to its neighbors, you can use "aggregation" below.
https://community.fortinet.com/t5/FortiGate/Technical-Tip-How-to-implement-BGP-route-summary-aggrega...

But I don't know if AWS side support route aggretation on its end. You can probably ask AWS support if they support or not. My guess is they would support though.

Toshi

[FortDoog]

Good day Toshi.

No, no, I don´t the device to summarize. What I want is for the firewall to accept those subnets that are /16, but using the prefix filter set in /11 (roughly speaking).

What I assumed, is that if I set the prefix list-in to /11 for certain subnet, it will accept ALL that is enclosed by the /11 subnet, meaning the /16, by setting the ge to 11.

But from what I saw, the prefix filter does not work like that. So I wanted to know how to do this correctly.

[Toshi_Esumi]

Then try this:
config router prefix-list
  edit "AWS-slash16s"
    config rule
      edit 1
        set prefix 10.160.0.0 255.248.0.0
        set ge 16
        set le 16
      next
      edit 2
        set prefix 10.64.0.0 255.240.0.0
        set ge 16
        set le 16
      next
    end
  next
end

Toshi

[FortDoog]

Thanks Toshi.

But, as I was telling Bill. I would like to have the ge set to 16, but not the le. To allow for prefixes higer than 16.

But then now I have a doubt.

Why I cannot use a prefix list in like this:

set prefix 10.160.0.0 255.224.0.0

set ge 11

Why the filter does not allow the /16 to be accepted?

[BillH_FTNT]

Yeah, that is seem invalid one. ge 11 is invalid. Should be ge 15

[jhonnymertin849]

You can control traffic preference for each tunnel by adjusting the BGP attributes such as local preference or MED (Multi-Exit Discriminator). This allows you to prioritize certain tunnels over others for outbound traffic. Additionally, you can use route maps or policies to influence inbound traffic preference. Consider exploring these 9anime options to fine-tune your setup for optimal performance. Good luck with your configuration.