S2C VPN

**Table 1** Constraints on VPN gateways
VPN Type	Resource	Default Quota	How to Increase Quota
Enterprise Edition VPN	VPN gateways per tenant in each region	50 If you have only one VPC, you can create a maximum of 50 VPN gateways for the VPC. If you have multiple VPCs, you can create a maximum of 50 VPN gateways for all these VPCs.	Submit a service ticket.
	VPN connection groups per VPN gateway	100 If a VPN gateway supports access via non-fixed IP addresses, it supports a total of 100 VPN connection groups for access via non-fixed IP addresses and access via fixed IP addresses.	This quota cannot be increased.
	Local subnets per VPN gateway	50	This quota cannot be increased.
	Number of BGP routes that a VPN gateway can receive from a customer gateway through a connection	100	This quota cannot be increased.
Classic VPN	VPN gateways per tenant in each region	2 Only one VPN gateway can be created for a VPC.	Submit a service ticket.

By default, the maximum length of TCP packets supported by a VPN gateway is 1300 bytes.

**Table 2** Constraints on customer gateways
VPN Type	Resource	Default Quota	How to Increase Quota
Enterprise Edition VPN	Customer gateways per tenant in each region	100	Submit a service ticket.

Enable NAT traversal on the customer gateway based on the networking.
- If the customer gateway is connected to the Internet through a NAT device, enable NAT traversal on the customer gateway.
- If the customer gateway is directly connected to the Internet, you do not need to enabled NAT traversal on the customer gateway.
Dead Peer Detection (DPD) must be enabled on a customer gateway.
A customer gateway must support IPsec tunnel interfaces and be configured with a corresponding security policy.
When Network Quality Analysis (NQA) is enabled for a connection in static routing mode, the IPsec tunnel interface of a customer gateway must have an IP address and be able to respond to ICMP requests.
It is recommended that the maximum segment size (MSS) of TCP packets be set to a value less than 1399 on a customer gateway, so as to prevent fragmentation caused by addition of an IPsec header.

**Table 3** Constraints on VPN connections
VPN Type	Resource	Default Quota	How to Increase Quota
Enterprise Edition VPN	Policy rules per VPN connection	5	The quotas cannot be increased.
Enterprise Edition VPN	Customer subnets per VPN connection	50	The quotas cannot be increased.
Classic VPN	VPN connections per tenant in each region	12	This quota cannot be increased.

In multi-subnet scenarios, you are advised to use VPN connections in routing mode. For a VPN connection in policy-based or policy template mode, a VPN gateway creates a communications tunnel for each pair of the local and customer subnets by default. If there are multiple local or customer subnets for a VPN connection in policy-based or policy template mode, multiple communications tunnels are created.
Each IP address of a VPN gateway supports a maximum of 100 communications tunnels for connecting to customer gateways.
- In routing mode, each VPN connection occupies only one communications tunnel of the corresponding VPN gateway IP address.
- In policy-based or policy template mode, each VPN connection occupies M x N communications tunnels of the corresponding VPN gateway IP address. M indicates the number of local subnets, and N indicates the number of customer subnets.
If the number of communications tunnels occupied by all VPN connections in different modes established by a single gateway IP address has reached 100, excess VPN connections will fail to be created.
When creating a VPN connection in policy-based mode and adding multiple policy rules, ensure that the source and destination CIDR blocks in different policy rules do not overlap. Otherwise, data flows may be incorrectly matched or IPsec tunnels may flap.