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Magic WAN allows you to achieve any-to-any connectivity across branch and retail sites and data centers, with Cloudflare connectivity cloud.

Magic WAN set up options

• Automatically: Through Magic WAN Connector (preferred method). You can choose between the hardware version or the virtual version of the Magic WAN Connector. The virtual version can be installed on your own machines. Refer to Configure with Connector for more information.
• Manually: Through a third-party device. Read the Prerequisites below before following the steps in Manual configuration.

Before you begin

Magic WAN is an Enterprise-only product. Contact Cloudflare ↗ to acquire Magic WAN. If you plan on using Magic WAN Connector to automatically onboard your locations to Cloudflare, you will need to purchase Magic WAN first.

Note

The list of prerequisites below is only for customers planning to connect manually to Cloudflare with a third-party device. If you plan on using Magic WAN Connector, refer to Configure with Connector.

Prerequisites

Use compatible tunnel endpoint routers

Magic WAN relies on GRE and IPsec tunnels to transmit packets from Cloudflare’s global network to your origin network. To ensure compatibility with Magic WAN, the routers at your tunnel endpoints must:

• Allow configuration of at least one tunnel per Internet service provider (ISP).
• Support maximum segment size (MSS) clamping.
• Support the configuration parameters for IPsec mentioned in IPsec tunnels.

Set maximum segment size

sequenceDiagram
accTitle: Magic WAN
accDescr: Maximum segment size
participant A as Client machine
participant B as Cloudflare Magic WAN/Transit
participant C as Origin router
A->>B: MSS = 1460 bytes <br> Protocol (20 bytes) <br> IP header (20 bytes)
Note left of A: SYN
B->>C: MSS = 1436 bytes <br> Protocol (20 bytes) <br> IP header (20 bytes) <br> GRE header (4 bytes) <br> IP header (20 bytes)
C->>A: MSS = 1436 bytes <br> IP <br> Protocol
Note right of C: SYN-ACK
A->>B: MSS = 1436 bytes <br> Protocol <br> IP
Note left of A: ACK
B->>C: Protocol <br> IP <br> GRE <br> IP

The SYN-ACK packet sent to the client during TCP handshake encodes the value for maximum segment size (MSS). Egress packets are routed via your ISP interface, and each packet must comply with the standard Internet routable maximum transmission unit (MTU), which is 1500 bytes.

Cloudflare Magic WAN uses tunnels to deliver packets from our global network to your data centers. Cloudflare encapsulates these packets adding new headers.

To accommodate the additional header data, you must set the MSS value to 1436 bytes at your tunnel interfaces (not the physical interfaces).

Important

Refer to your device documentation to check if it sets IPsec MSS clamping automatically. If that is not the case and you are using IPsec inside GRE, you have to set MSS clamp manually.

Set MSS clamp at the IPsec tunnel interface and subtract 24 bytes from your current MSS value, which may be 1360 bytes or lower. This is because the physical interface will see IPsec-encrypted packets, not TCP packets, and MSS clamping will not apply to those.

Standard Internet Routable MTU	1500 bytes
- Original IP header	20 bytes
- Original protocol header (TCP)	20 bytes
- New IP header	20 bytes
- New protocol header (GRE)	4 bytes
= Maximum segment size (MSS)	1436 bytes

Unless you apply these MSS settings at the origin, client machines do not know that they must use an MSS of 1436 bytes when sending packets to your origin.

Follow router vendor guidelines

Instructions to adjust MSS by applying MSS clamps vary depending on the vendor of your router.

The following table lists several commonly used router vendors with links to MSS clamping instructions:

Router device	URL
Cisco	TCP IP Adjust MSS ↗
Juniper	TCP MSS – Edit System ↗