Question

How to create a firewall rule to allow TCP, UDP and ICMP traffic from a peer network to GCP network?

Answer 1

You could probably execute the firewall-rules create command as shown: 

 gcloud  compute --project project-id firewall-rules create vpnrule1 \
    --network network \
    --allow tcp,udp,icmp \
    --source-ranges peer-source-range

If you have more than one peer network range, provide a comma-separated list in the source-ranges field (--source-ranges 192.168.1.0/24,192.168.2.0/24).