tencent cloud


Security Groups

Last updated: 2022-04-13 11:01:52

    Why does a security group have a reject rule by default?

    Security group rules take effect in sequence from top to bottom. After a preceding allow rule is applied, other rules are ignored by default. If all ports are open to the internet, the last deny rule does not take effect. We provide this default configuration for security reasons.

    How can I adjust the priority of a security group?

    For more information, see Adjusting Security Group Priority.

    If I bind an incorrect security group to an instance, what impact will this have on the instance? How can I fix this problem?

    Potential problems

    • You may fail to remotely connect to a Linux instance over SSH or a Windows instance via remote desktop.
    • You may fail to remotely ping the public IP and private IP addresses of the CVM instance in this security group.
    • You may fail to access over HTTP the web services exposed by the CVM instance in this security group.
    • The CVM instance in this security group may fail to access Internet services.


    • If any of the aforementioned problems occur, you can go to Security Groups in the console and modify the security group rule. For example, you can change the rule to "bind only all-ports-open security groups by default".
    • For more information on how to set a security group rule, see Security Groups.

    What do the security group direction and policy mean?

    The security group policies involve inbound and outbound directions. Outbound policies are used to filter outbound traffic from the CVM, and inbound policies are used to filter inbound traffic to the CVM.
    Security group policies are divided into those that allow and refuse traffic.

    In which order do the security group policies take effect?

    Security group policies take effect from top to bottom. When traffic passes through the security group, policy matching is performed from top to bottom. A policy takes effect once matching is successful.

    Why can an IP address that is rejected by a security group still access the CVM instance?

    Possible reasons:

    • The CVM is bound to multiple security groups, and this IP address is allowed by another security group among them.
    • This IP address belongs to an approved Tencent Cloud public service.

    Can iptables be used along with security groups?

    Yes, iptables and security groups can be used at the same time. Your traffic will be filtered twice as follows:

    • Outbound: processes in your instance > iptables > security groups.
    • Inbound: security groups > iptables > processes in your instance.

    Why can't security groups be deleted even though all CVM instances have been returned?

    Check whether there are still bound CVMs in the recycle bin. The security group cannot be deleted even if it is bound to a CVM in the recycle bin.

    Can the name of a cloned security group be the same as that of a security group in the target region?

    No. The name must be different from names of existing security groups in the target region.

    Can a security group be cloned across different users?


    Can I clone a security group to another project or region using an API?

    To facilitate the use of the console, we provide MC support but not cloud API support. You can use the cloud APIs for importing and exporting security group rules in batches to clone security groups across projects and regions.

    When I clone a security group across projects and regions, will CVM instances managed by the security group also be copied?

    No. Only the inbound and outbound rules of the security group are cloned. You need to associate CVMs again after cloning.

    What is a security group?

    A security group is a virtual firewall that features stateful data packet filtering. It is used to configure the network access control of CVM, Cloud Load Balancer, TencentDB, and other instances while controlling their outbound and inbound traffic. It is an important means of network security isolation.

    Each CVM instance is bound to at least one security group, which must be specified when the instance is created. CVM instances are interconnected in the same security group but cannot communicate with CVM instances across security groups. However, you can authorize the interconnection between two security groups. For more information, see Security Groups.

    Why do I need to choose a security group when creating CVM instances?

    Before creating CVM instances, you must choose a security group to partition the security domains of the application environment and authorize the security group rules to properly implement network security isolation.

    What should I do when I create CVM instances if I have not created a security group?

    In this case, you can create a security group.
    A security group supports the following rules. You can open IPs and ports as needed.

    • ICMP: opens to the ICMP protocol and allows the pinging of the server over the public network.
    • TCP:80: opens port 80 and allows access to Web services over HTTP.
    • TCP:22: opens port 22 and allows a remote connection to Linux CVMs over SSH.
    • TCP:443: opens port 443 and allows access to Web services over HTTPS.
    • TCP:3389: opens port 3389 and allows a remote connection to Windows CVMs over RDP.
    • Open the private network: opens to the private network and allows private network access among different cloud resources (IPv4).

    In what situations will the default security group rule be used to a security group?

    The default security group rule will be used in the following situations:

    • When creating a CVM instance, if you select Quick Configuration to purchase the instance, the system will automatically create a default security group for you, which will adopt the default security rule (i.e., allowing all IPv4 addresses).
      However, for security reasons, we recommend you associate your CVM with a new security group that only opens ports when absolutely necessary to avoid unnecessary security risks.
    • You can choose a template when creating a security group in the CVM console. Currently, supported templates include Windows login, Linux login, Ping, HTTP(80) and HTTPS(443).
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