This topic describes the limits of Express Connect that you must take note of before you get started.
Limits on resources
|The maximum number of allowed prefixes that each virtual border router (VBR) can advertise||20|
|The maximum number of Express Connect circuits that can be connected to an access point with each Alibaba Cloud account||2|
|The maximum number of routes that each BGP peer in a BGP group can receive||110|
|The maximum number of peering connections that can be established in each VPC||5|
|The maximum number of peering connections that each VBR can establish||5|
|The maximum number of peering connections, including virtual private cloud (VPC) and VBR connections, that can be established with each Alibaba Cloud account||10|
|The maximum number of VBRs that can be created for an Express Connect circuit after you enable billing for outbound data transfer||10|
|Allows you to query the locations of access points||0|
|The maximum number of routes that can be configured on each VBR||48||N/A|
|The maximum number of BGP CIDR blocks that each VBR can advertise||10|
|The maximum number of unpaid Express Connect circuits that can be created||10|
|The maximum number of VBRs that can be associated with a shared port||1|
Limits on networks
To connect a data center to Alibaba Cloud over an Express Connect circuit, make sure that the CIDR blocks of services on Alibaba Cloud and the CIDR blocks of the data center do not conflict with each other. You must also make sure that the data center meets the following requirements:
- If you use optical fiber cables, you must use one of the following types of single-mode optical transceiver modules to connect to the access device of Alibaba Cloud. The configurations of the optical transceiver modules must be the same on both ends of the connection.
- 1000 Base-LX single-mode optical transceiver module
- 10 GBase-LR single-mode optical transceiver module
- 40 GBase-LR single-mode optical transceiver module
- 100 GBase-LR single-mode optical transceiver module
- You must disable auto-negotiation for the port. Then, specify the port rate and set the duplex mode to full-duplex.
- All devices used to establish the connection support 802.1Q VLAN encapsulation, including the intermediary devices in data centers.
- The gateway device in your data center must support BGP and BGP MD5 authentication or static routing.
- To use a redundant Express Connect circuit, you must set route weights on your gateway device.
- The maximum transmission unit (MTU) on the physical layer is 1,522 bytes, including the 14-byte Ethernet header, 4-byte VLAN flag, 1,500-byte IP datagram, and 4-byte frame check sequence (FCS).
Recommended value: 1500.
- We recommend that you use private IP addresses to establish the connection between your data center and Alibaba Cloud. In addition, the CIDR blocks specified for the connection must not conflict with each other.
- You must not set the CIDR block of the data center to 100.64.0.0/10 in case it conflicts with the CIDR blocks of the services on Alibaba Cloud.
- You must not specify 100.64.0.0/10 as the peer CIDR block for the VBR on Alibaba Cloud or the gateway device in the data center.
- The gateway device in the data center must be able to receive more than 500 Internet Control Message Protocol (ICMP) echo requests per second. Otherwise, the gateway device cannot promptly respond to probe packets sent for health checks and consequently network jitter occurs.
Limits on transmission rates (Alibaba Cloud side)
Data transmission between a VPC and a data center is throttled when you use an Express Connect circuit. In addition, the communication between a VPC and a data center is throttled due to the following reasons:
- The maximum read/write speed for Object Storage Service (OSS) is 10 Gbit/s.
- To improve reliability, the transfer of individual hashed traffic flow from a VPC to a VBR is throttled. The transmission rate is throttled to 1/12, 1/4, 1/8, or 1/16 of the bandwidth limit that you specify when you create a peering connection. For example, if the bandwidth limit of a peering connection between a VPC and a VBR is set to 1 Gbit/s, the transfer of individual hashed traffic flow from the VPC to the VBR is throttled to 85 Mbit/s.
A hashed traffic flow is a data stream that is defined by the combination of the source IP address, source port, transport layer protocol, destination IP address, and destination port. For example,
192.168.1.1 10000 TCP 121.XX.XX.76 80forms a hashed traffic flow. In this traffic flow, a terminal that is assigned the IP address 192.168.1.1 and port 10000 is connected to a terminal that is assigned the IP address 121.XX.XX.76 and port 80 over TCP.
Limits on access points
Before you connect a data center to Alibaba Cloud over an Express Connect circuit, you must choose an access point. Take note of the following limits before you choose an access point:
- A region provides multiple access points located in different zones. The network latency between two access points located in zones of the same region is lower than 5 milliseconds.
- If you want to minimize the network latency, you can Submit a ticket for information about the access point nearest to your cloud servers.
Limits on Express Connect circuits
- Before you use Express Connect, you must plan the CIDR blocks of the VPC and the data center that you want to connect. Make sure that the CIDR blocks of the VPC and the data center do not overlap with each other.
- Cloud services deployed in VPCs use the 100.64.0.0/10 CIDR block. Therefore, data centers that are connected to VPCs over Express Connect circuits must not use the 100.64.0.0/10 CIDR block.
- Alibaba Cloud provides optical transceiver modules with 1 Gbit/s and 10 Gbit/s ports for you to connect your data center to access points. These optical transceiver modules support a maximum transmission distance of 10 km. If you want to use optical transceiver modules with 40 Gbit/s and 100 Gbit/s ports or optical transceiver modules that support a maximum transmission distance greater than 10 km, purchase them from a third party.
- Express Connect circuits do not support virtual extensible local area network (VXLAN) traffic (UDP protocol whose destination port is 4789).
Limits on redundant Express Connect circuits
- Alibaba Cloud guarantees service availability for connections over Express Connect circuits only when the Express Connect circuits are connected to different access points. If multiple Express Connect circuits share the same access point or only one Express Connect circuit is used, service availability is not guaranteed.
- If a data center is connected to a VPC over two Express Connect circuits, you must specify source IP addresses and destination IP addresses for health checks. After you configure health checks for the Express Connect circuits, the system checks the status of both Express Connect circuits. If one of the Express Connect circuits is down, network traffic is transmitted over the other Express Connect circuit. We recommend that you configure health checks to detect service interruptions. This way, the system can perform failovers at the earliest opportunity.
Limits on hosted connections over Express Connect circuits
- Alibaba Cloud cannot change the port settings to meet your business requirements.
- Equal-cost multi-path routing (ECMP) is not supported.
- When you set a bandwidth limit on a hosted connection over an Express Connect circuit, make sure that the sum of the bandwidth limits of all hosted connections does not exceed the bandwidth limit of the Express Connect circuit.
Limits on Express Connect circuit installation
- The company in charge of the installation of an Express Connect circuit must follow the construction rules stipulated by connectivity providers and engineers of the Alibaba Cloud data center. Installation is forbidden in case of violation.
- If you purchase optical ports, make sure that the connectivity provider uses optical fiber cables to connect to the port of Alibaba Cloud.
- If you purchase copper Ethernet ports, make sure that the connectivity provider uses copper cables to connect to the port of Alibaba Cloud.
- Alibaba Cloud data centers do not support fiber-optic transceivers. The company in charge of the installation cannot install fiber-optic transceivers in data centers of Alibaba Cloud.
- The installation schedule is subject to data center lockdowns required by local authorities and Alibaba Cloud. If the data center is locked down, you can contact your account manager.
- Data centers where Alibaba Cloud access points are located are leased from the telecom service provider or third-party service providers. Therefore, you may be charged by a service provider for installing the Express Connect circuit in their buildings and using the indoor cables.
Time spans for Express Connect circuit installation
The following table describes the time required for installing Express Connect circuits.
|Review of the application to enter an Alibaba Cloud data center and perform site surveys for the installation||Two business days|
|Review of the application for a Letter of Authorization (LOA)||Two business days|
|Fiber pigtail installation||Optical transceiver modules provided by Alibaba Cloud|
Optical transceiver modules provided by a third party
|Review of the application to enter an Alibaba Cloud data center to maintain an Express Connect circuit||Two business days|