Sdwan Asymetric

Forum|Forum|10 months ago
September 21, 2025
6 replies
664 views

I have 2 site to site from site-A to site-B and sdwan only enabled in site-A

In the site-B I configure static route to site-A via 2 link with same cost.

The issue is when site-A select link-B for example then site B reply using link-A.

How we can prevent this kind of asymetric?

FortiGate

AEK

SuperUser

No SD-WAN in site B.

This one should be fixed with policy route.

AEK

Toshi_Esumi

SuperUser

If 1) site B is a FGT, 2) those two interfaces at site-B back to site-A are NOT in an SD-WAN group, and 3) those are really "reply/returning" packets, it should never happen. Because the site-B FGT has a session established to return the session's returning packet to the interface the initiation packet came in.
so, those are either a) not reply packets but initiated by site-B, or 2) the site-B doesn't have a proper route to the interface the initiation packet came in.

Toshi

HS08Author

Contributor III

Both site using Fortigate, when connection from site-A to site-B via link-A have bad performance, i can see in fortigate session site-A the traffic flowing to the link-B.

But when i check session in site-B, the traffic is using link-A.

Toshi_Esumi

SuperUser

Because the link was changed while the session is still alive. Site-B needs to have the same members in an SD-WAN zone, then the same session on the B-side should still work. You probably want to set the same rules and SLA settings on the B-side so that it fails over to the other side for B-initiated session.

Toshi

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