So I can only speculate whether this is a potential problem. If it calculates it from the IP header, then the UDP length is validated. If it does it the lazy way, and constructs the pseudo-header using the length explicitly declared in the UDP header, then there is no check on the length at all. I suppose this hinges on how the UDP header checksum algorithm is implemented in the receiver. So if you wanted to fiddle the UDP length, you would also have to fiddle the IP header octets 2+3, and therefore also IP header octets 10+11, and therefore also. But as far as the receiver is concerned, they come from different places: the real field from the UDP header is explicit, and the pseudo field is calculated from the IP packet length (IP octets 2+3), minus 4 * IP-HLEN. É opcional no IPv4, mas foi obrigatório no IPv6. This is what I think now: as far as the transmitter is concerned, the two fields (real and pseudo) come from the same place: the length of the user datagram data. UDP checksum opcional: A soma de verificação permite que o dispositivo receptor verifique a integridade do cabeçalho do pacote e da carga útil. So you can change the field as much as you like, and it wouldn't make a ha'p'orth of difference. I reasoned like this: the checksum is a 1's complement, so if you include a field twice in the calculation, the net effect of the field is zero. If the UDP length was changed between the source and destination, the checksum discrenpency would just be double what it would be if we only included the length value once. I don't know whether /dev/udp "really exists" on Solaris.At first sight, I didn't agree with you about ". To drop packets with incorrect checksums in the IP header by enforcing IP header checksums, select Enable IP header checksum enforcement. Scroll to IP and UDP Checksum Enforcement. (On Linux and FreeBSD, /dev/udp "doesn't really exist" it's a fiction provided by Bash. IP and UDP Checksum Enforcement To configure IP and UDP checksum enforcement: Navigate to Device > Firewall Settings > Advanced. This parameter controls whether UDP calculates the checksum Also, even the Solaris docs say: udp_do_checksum The ndd utility is specific to the Solaris kernel, and does not exist on Linux or FreeBSD. This -ip post from 1999 suggests that on Solaris, you can globally disable the generation of UDP checksums on outgoing packets via ndd at the command line: ndd -set /dev/udp udp_do_checksum 0 RFC 8085: "An application is permitted to optionally discard UDP datagrams with a zero checksum. If you just take your platform's default behavior, you will get UDP checksum generation by default - I'd put money on it. I've collected some ways below, which might or might not work caveat lector. By default TCP and UDP checksum validation is disabled for packets that are decoded and displayed within CDRouters web UI: Checksum validation may be. The only thing you might possibly be able to control is whether the sending interface generates checksums on outgoing packets. The receiving interface MAY drop packets with no checksum, or MAY pass them on to the application (or MAY let the application configure its desired behavior, although if this is possible, I don't know how to do it). That's just a mandatory part of the UDP standard. Therefore, you are never allowed to disable UDP checksum checking on incoming packets (if those packets have checksums provided, that is). Checksum is a simple error detection mechanism to determine the integrity of the data transmitted over a network. "negative zero" in the ones' complement encoding used by the checksum field) and MUST drop the packet if it fails the check. It is optional in IPv4 but was made mandatory in IPv6. Checksum The checksum allows the receiving device to verify the integrity of the packet header and payload. A checksum of all-bits-zero means "The outgoing interface didn't generate a checksum." The interface MUST check any other checksum (including all-bits-one, a.k.a. The limit for the UDP length field is determined by the underlying IP protocol used to transmit the data. The network interface (or driver or something equivalent) should be checking the checksums of incoming packets.
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