> Source: [sk182359](https://support.checkpoint.com/results/sk/sk182359)

# sk182359 - IPv6 packet drop with "[ILLEGAL CHECKSUM (0)]" error

| Property | Value |
|----------|-------|
| Solution ID | sk182359 |
| Date Created | 2024-06-02 |
| Last Modified | 2024-06-10 |
| Technical Level | Advanced |
| Products | Security Gateway |
| Versions | R81.20, R81.10 (EOS) |
| OS | Gaia |

## Symptoms

- IPv6 packet drop on the Security Gateway. In the debug output of "`fw ctl zdebug + drop`" you see the error: `"[ILLEGAL CHECKSUM (0)]"`.

## Cause

[RFC 2460](https://datatracker.ietf.org/doc/html/rfc2460) states that "Unlike IPv4, when UDP packets are originated by an IPv6 node, the UDP checksum is not optional."

If a checksum computation yields the value zero, it should be changed to FFFF for placement in the UDP header.

However, for certain protocols that use UDP as a tunnel encapsulation, the UDP checksum zero can be enabled.

The default Security Gateway behavior is to drop packets with zero checksum.

## Solution

This solution requires authentication. Please log in to view the full solution.

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