Counts received UDP datagrams that couldn't be delivered for reasons other than no application listening at the destination port, for example checksum errors or malformed headers. Because no-listener cases are excluded, a rising udpInErrors specifically points to malformed or corrupted UDP traffic reaching the gateway's own stack, useful for spotting either a flaky link corrupting UDP packets or crafted UDP packets targeting services like the VPN's IKE port. Example: udpInErrors rising specifically on the IKE port used for VPN negotiation would be worth investigating as malformed IKE packets, whether from a buggy peer or a deliberate probe.