diff options
Diffstat (limited to 'pkg/tcpip/tcpip.go')
| -rw-r--r-- | pkg/tcpip/tcpip.go | 26 |
1 files changed, 26 insertions, 0 deletions
diff --git a/pkg/tcpip/tcpip.go b/pkg/tcpip/tcpip.go index 21aafb0a2..a634b9b60 100644 --- a/pkg/tcpip/tcpip.go +++ b/pkg/tcpip/tcpip.go @@ -43,6 +43,9 @@ import ( "gvisor.dev/gvisor/pkg/waiter" ) +// Using header.IPv4AddressSize would cause an import cycle. +const ipv4AddressSize = 4 + // Error represents an error in the netstack error space. Using a special type // ensures that errors outside of this space are not accidentally introduced. // @@ -320,6 +323,29 @@ func (s *Subnet) Broadcast() Address { return Address(addr) } +// IsBroadcast returns true if the address is considered a broadcast address. +func (s *Subnet) IsBroadcast(address Address) bool { + // Only IPv4 supports the notion of a broadcast address. + if len(address) != ipv4AddressSize { + return false + } + + // Normally, we would just compare address with the subnet's broadcast + // address but there is an exception where a simple comparison is not + // correct. This exception is for /31 and /32 IPv4 subnets where all + // addresses are considered valid host addresses. + // + // For /31 subnets, the case is easy. RFC 3021 Section 2.1 states that + // both addresses in a /31 subnet "MUST be interpreted as host addresses." + // + // For /32, the case is a bit more vague. RFC 3021 makes no mention of /32 + // subnets. However, the same reasoning applies - if an exception is not + // made, then there do not exist any host addresses in a /32 subnet. RFC + // 4632 Section 3.1 also vaguely implies this interpretation by referring + // to addresses in /32 subnets as "host routes." + return s.Prefix() <= 30 && s.Broadcast() == address +} + // Equal returns true if s equals o. // // Needed to use cmp.Equal on Subnet as its fields are unexported. |