Well you could do it like this... You first define a group policy with the rules you need. Something like this:
![group_policy_block_all.PNG group_policy_block_all.PNG](https://community.meraki.com/t5/image/serverpage/image-id/5743i442B2F536734997C/image-size/large?v=v2&px=999)
Then, in the Addressing & VLANs section in the MX, in the VLAN you want to restrict, you select the group policy you just created in the dropdown:
![group_policy_applied_to_vlan.PNG group_policy_applied_to_vlan.PNG](https://community.meraki.com/t5/image/serverpage/image-id/5744i26B32D333F3B71A7/image-size/large?v=v2&px=999)