"TFTP is a UDP-based protocol. Servers listen on port 69 for the initial client-to-server packet to establish the TFTP session, then use a port above 1023 for all further packets during that session. Clients use ports above 1023" https://docstore.mik.ua/orelly/networking_2ndEd/fire/ch17_02.htm Besides, Google Cloud external TCP/UDP Network Load Balancing (after this referred to as Network Load Balancing) is a regional, non-proxied load balancer. Network Load Balancing distributes traffic among virtual machine (VM) instances in the same region in a Virtual Private Cloud (VPC) netw

Google Cloud VPC Network Peering allows internal IP address connectivity across two Virtual Private Cloud (VPC) networks regardless of whether they belong to the same project or the same organization.

Create Packet Mirroring Policies:
You need to create three packet mirroring policies, one for each zone (us-west2-a, us-west2-b, and us-west2-c). This ensures that each zone's traffic is mirrored appropriately without unnecessary cross-zone traffic.
Create Collector Instances:
Set up one group of collector instances for the us-west2 region. Having a single group of collector instances for the entire region minimizes the number of instances required and simplifies the management while keeping egress costs low since the collectors are within the same region.
Configuration of Policies:
Each packet mirroring policy should be configured to match traffic for its specific zone. Use instance-tags to identify and match the relevant instances within each zone. This helps in correctly capturing the traffic from the appropriate sources.
Filter for TCP Traffic:
Create a filter for TCP traffic (ports 80 and 443). This step ensures that only the relevant web application traffic is mirrored, reducing the amount of data processed and improving efficiency.
Cost Efficiency:
By having packet mirroring policies specific to each zone and a regional collector group, you reduce inter-zonal network egress costs. The data remains within the same region, avoiding extra charges associated with cross-zone traffic.
Reference:
Google Cloud Packet Mirroring Documentation
Best Practices for Packet Mirroring
Cost Management in Google Cloud
This solution aligns with Google-recommended practices by ensuring efficient traffic capture, minimal inter-zonal costs, and streamlined management of the packet mirroring setup.

https://cloud.google.com/load-balancing/docs/load-balancing-overview mentions to use global load balancer for IPv6 termination.