Cisco ASA site to site packets only go one way


I have an issue with one site connecting to head office. There are three other sites already having site to site VPNs with head office and they work reliably. There is not much to get wrong in the wizard, it is simple enough but with this site the VPN gets set up but the remote site is receiving no packets from the head office. Looking at the head office ASA I see it is receiving packets but sending nothing.
However, sometimes by rebooting one or the other firewalls (or even both) the VPN will work correctly for anything from a few hours to a few weeks before reverting back to the situation above.

All the branch offices are running OS version 9.6(1)

Does anyone have any ideas please?

Thank you.

Alasdair Barclay
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So it works periodically, double check the VPN config on both sides to make sure there is no mismatch key lifetime, amount of satadata transferred.

Events on either that might explain the issue.
Does either side have more than one wan/ISP connections?
Show crypto isakmp
show crypto IPSec sa

Another connection using a similar ip segment on their LAN.

Site1 to site2
Site1 to site3
Depending on which sets up first, site2 and site3 have overlapping, same segments

Site2 or site3 to site1 works, but site1 to the other may be impacted by which VPN sets up first.

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ArchiTech89IT Security EngineerCommented:
I would also look at the ACL that's generating "interesting traffic" for the VPN. It might be that the ACL on the far side is set up so that the traffic properly traverses, but the head office has a typo or some other reason why interesting traffic isn't being generated.

You can always check the status of the VPN in ASDM by going to Monitoring | VPN | Sessions where you can Filter By: IPsec Site-to-Site to see the status and information about each of the VPNs.

Would you care to post the aspects of the run config for this VPN (with appropriate info obscured, obviously)?

AlasdairbAuthor Commented:
Thanks to both.
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