diff options
Diffstat (limited to 'pkg/tcpip/header/ipv4.go')
| -rw-r--r-- | pkg/tcpip/header/ipv4.go | 26 |
1 files changed, 26 insertions, 0 deletions
diff --git a/pkg/tcpip/header/ipv4.go b/pkg/tcpip/header/ipv4.go index 85bd164cd..2be21ec75 100644 --- a/pkg/tcpip/header/ipv4.go +++ b/pkg/tcpip/header/ipv4.go @@ -455,6 +455,32 @@ func IsV4LinkLocalMulticastAddress(addr tcpip.Address) bool { return ipv4LinkLocalMulticastSubnet.Contains(addr) } +// IsChecksumValid returns true iff the IPv4 header's checksum is valid. +func (b IPv4) IsChecksumValid() bool { + // There has been some confusion regarding verifying checksums. We need + // just look for negative 0 (0xffff) as the checksum, as it's not possible to + // get positive 0 (0) for the checksum. Some bad implementations could get it + // when doing entry replacement in the early days of the Internet, + // however the lore that one needs to check for both persists. + // + // RFC 1624 section 1 describes the source of this confusion as: + // [the partial recalculation method described in RFC 1071] computes a + // result for certain cases that differs from the one obtained from + // scratch (one's complement of one's complement sum of the original + // fields). + // + // However RFC 1624 section 5 clarifies that if using the verification method + // "recommended by RFC 1071, it does not matter if an intermediate system + // generated a -0 instead of +0". + // + // RFC1071 page 1 specifies the verification method as: + // (3) To check a checksum, the 1's complement sum is computed over the + // same set of octets, including the checksum field. If the result + // is all 1 bits (-0 in 1's complement arithmetic), the check + // succeeds. + return b.CalculateChecksum() == 0xffff +} + // IsV4MulticastAddress determines if the provided address is an IPv4 multicast // address (range 224.0.0.0 to 239.255.255.255). The four most significant bits // will be 1110 = 0xe0. |