Please be advised, there is a current issue with PAN-OS 8.1 which seems to break anything SMB related, e.g. mapped network drives. Sessions have an end reason of "resources-unavailable" and go into state "Discard" in the session table.
Upon speaking with a TAC engineer, this is a known issue and they are working towards a fix.
Edit: This is now resolved in PAN-OS 8.1.1 under BugID:
Fixed an issue where Server Message Block (SMB) sessions were in a discard state with the session end reason resources-unavailable
So far I've had no issues with 8.1 och PA-220, not that much traffic passing through it though...
On a couple of PA-850 the only option was to do a downgrade, no SMB traffic worked as intended.
Could it be related to certian hardware platforms? What platforms have you experienced problems on?
Re: Application Override to resolve PAN OS 8.1.0 SMB Issues
Does this apply to environments where the Palo Alto firewall provides routing to the local LAN and IPSEC tunnels to remote LANs on internal trusted interfaces where no Security or NAT policies are programmed?
If so, which applications need to be overridden to work-around this bug?
This is a devastating issue when it occurs.
Our work-sround has been to switch the active and passive roles of 2 PA-500 firewalls to reset the routing. This restores LAN and IPSEC tunnel routing for SMB but only works until the problem returns.
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