docs/en-US/about-security-groups.xml

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<section id="about-security-groups">
    <title>About Security Groups</title>
    <para>Security groups provide a way to isolate traffic to VMs. A security group is a group of
        VMs that filter their incoming and outgoing traffic according to a set of rules, called
        ingress and egress rules. These rules filter network traffic according to the IP address
        that is attempting to communicate with the VM. Security groups are particularly useful in
        zones that use basic networking, because there is a single guest network for all guest VMs.
        In advanced zones, security groups are supported only on the KVM hypervisor.</para>
    <note><para>In a zone that uses advanced networking, you can instead define multiple guest networks to isolate traffic to VMs.</para>
        </note>
    <para></para>
    <para>Each &PRODUCT; account comes with a default security group that denies all inbound traffic and allows all outbound traffic. The default security group can be modified so that all new VMs inherit some other desired set of rules.</para>
    <para>Any &PRODUCT; user can set up any number of additional security groups. When a new VM is launched, it is assigned to the default security group unless another user-defined security group is specified. A VM can be a member of any number of security groups. Once a VM is assigned to a security group, it remains in that group for its entire lifetime; you can not move a running VM from one security group to another.</para>
    <para>You can modify a security group by deleting or adding any number of ingress and egress rules. When you do, the new rules apply to all VMs in the group, whether running or stopped.</para>
    <para>If no ingress rules are specified, then no traffic will be allowed in, except for responses to any traffic that has been allowed out through an egress rule.</para>
</section>