Gateway Load Balancer (GWLB) is a load balancer that functions at the third layer (network layer) of the Open Systems Interconnection (OSI) model, enhancing the security and availability of application systems by transparently distributing traffic to different backend servers. This topic describes the key terms of GWLB instances.
Instance status
The following table describes the different states of a GWLB instance and whether the specified operations are supported.
Instance state | State description | Whether instance locked and why | Instance deletion allowed | Instance configuration update allowed |
Running | The instance is running as expected. | N/A | Yes | Yes |
Creating | The instance is being created. | N/A | No | No |
Updating Configuration | The configuration of the instance is being updated. | N/A | No | |
Stopped | The instance stops running. | Locked (Overdue Payment): The instance is locked due to overdue payments. Renew your instance at your earliest opportunity. The instance resumes providing services after it is unlocked. | No |
IP version
GWLB instances support IPv4 traffic access.
A GWLB instance communicates with backend servers using a private IPv4 address, which is assigned by the subnet where the GWLB instance resides.
Cross-zone forwarding
GWLB instances forward traffic across zones by default. When a GWLB instance in a region receives requests, the GWLB instance distributes the requests to the backend servers in all available zones of the region. Currently, the cross-zone forwarding feature cannot be disabled.
Network MTU
The maximum transmission unit (MTU) is a measurement of the largest data packet a device can accept via a network connection.
The MTU is the size of the largest protocol data unit (PDU) that can be communicated in a singlenetworklayer transaction.
The MTU of a network connection is the size of the largest packet that can be transmitted over the connection. An MTU includes the size of IP headers and payload and excludes the size of Ethernet headers.
GWLB MTU:
The maximum packet size supported by GWLB is 1500 bytes. Therefore, any packet exceeding 1500 bytes will be discarded and not transmitted.
MTU Settings for Network Virtual Devices:
When a GWLB instance encapsulates IP traffic with a Geneve header to forward it to a network virtual device, consider the additional 68 bytes added by the Geneve encapsulation to the original packet. It is recommended to set the MTU of the network virtual device to at least 1568 bytes (1500 bytes for the original packet size plus 68 bytes for the Geneve header encapsulation) to ensure it can handle packets up to 1500 bytes.
IP Fragmentation:
GWLB does not support IP fragmentation. If the original packet size exceeds 1500 bytes, it cannot be fragmented into smaller segments for transmission.
Path MTU Discovery (PMTUD):
GWLB does not generate ICMP messages to indicate fragmentation is needed, so PMTUD is not supported.
Idle connection timeout period
The idle connection timeout period specifies a timeout period for idle connections. Unit: seconds. Valid values: 1 to 60. To specify a longer timeout period,
The connection idle timeout is the maximum duration that a network connection can remain idle without data transmission. If no connection requests occur within the idle timeout period, the current connection is closed, and the GWLB instance routes new traffic to a new backend server. Existing traffic is discarded until a new connection is established upon the next request.
For TCP traffic, the connection idle timeout is 350 seconds.
For non-TCP traffic, the connection idle timeout is 120 seconds.
The connection idle timeout for GWLB instances cannot be modified.