Problem in specifying the network in cloud dataflow

It looks like your default firewall rules were modified and dataflow detected this and prevented your job from launching. Could you verify your firewall rules were not modified in your project?. Please take a look at the documentation here. You will also find a command here to restore the firewall rules:

gcloud compute firewall-rules create [FIREWALL_RULE_NAME] \
    --network [NETWORK] \
    --action allow \
    --direction ingress \
    --target-tags dataflow \
    --source-tags dataflow \
    --priority 0 \
    --rules tcp:1-65535

Pick a name for the firewall, and provide a network name. Then pass in the network name with --network when you launch the dataflow job. If you have a network named 'default' dataflow will try to use that automatically, so you won't need to pass in --network. If you've deleted that network you may wish to recreate it.

As of now, till apache beam version 2.19.0. There is no provision from dataflow to set network tag for its VM. Instead while creating firewall rule, we should add a tag for dataflow.

gcloud compute firewall-rules create FIREWALL_RULE_NAME \
    --network NETWORK \
    --action allow \
    --direction DIRECTION \
    --target-tags dataflow \
    --source-tags dataflow \
    --priority 0 \
    --rules tcp:12345-12346

See this link for more details https://cloud.google.com/dataflow/docs/guides/routes-firewall