topic ECMP breaks secure email access. in General Topics

ECMP breaks secure email access.

SShnap — Wed, 30 Apr 2025 16:57:00 GMT

Hi all,

while using ECMP for the last 2 years without any issues using 3 ISP's with different weight and enabling Symmetric Return and Strict Source Path, I found that some sites with authentication access and Proofpoint secure emails access are being timed out

because of their sensitivity of the source ISP change during the session.

In most of the cases creating BPF rule using address group for all those site's FQDN resolve the issue, but I'm looking for a way to using BPF based on URL category like Banks\financial sites.

Anyone face the same issue and solved it with a different approach?

Thank you for the help.

Re: ECMP breaks secure email access.

TomYoung — Wed, 30 Apr 2025 17:51:30 GMT

Hi @SShnap ,

I had similar issues with 1 customer. Changing the ECMP Load Balance Method from IP Modulo (default) to IP Hash caused all sessions with the same source/destination to always go out the same interface. This eliminated the need for PBF, and the applications worked properly. You could also check the box so that all traffic from a source IP address always goes out the same interface.

It appeared that the problem was that the web application wanted all traffic from the same source to have the same IP. This change fixed the issue.

Thanks,

Tom

Re: ECMP breaks secure email access.

SShnap — Wed, 30 Apr 2025 19:00:11 GMT

@TomYoung Thank you for the comment, so if I'm going to IP Hash route, I need to remove the PBF and there is no weight consideration?

Currently I'm using 2 ISP with same weight and 3rd ISP for backup with lower weight.

I will check this option later and see the results.

Thank you

Re: ECMP breaks secure email access.

TomYoung — Wed, 30 Apr 2025 19:07:12 GMT

Hi @SShnap ,

No, there is no weight consideration with IP Hash. https://docs.paloaltonetworks.com/pan-os/10-1/pan-os-networking-admin/ecmp/ecmp-load-balancing-algorithms

IP Hash balances over all links the same. If you want the 3rd ISP for backup, you can give it a higher metric.

I'm sure you already know this, but it is safer to disable PBF for now rather than remove. Rollback becomes much faster.

Thanks,

Tom

Re: ECMP breaks secure email access.

SShnap — Tue, 06 May 2025 15:59:37 GMT

@TomYoung Thank you for the response, I still want to use the PBF because some of the services are being allowed based on the ISP interface outbound.

Do you know what is prioritize first if we are using IP Hash and PBF?

I meant disable before removing them completely, thank you for the clarification.

Re: ECMP breaks secure email access.

TomYoung — Tue, 06 May 2025 16:22:59 GMT

Hi @SShnap ,

PBF takes priority over routing. https://docs.paloaltonetworks.com/pan-os/11-1/pan-os-admin/policy/policy-based-forwarding

Thanks,

Tom