Technical Q&A
NW 62 - TCP/IP Option Sizes (26-April-1999)
Q: I'm confused by the size of various TCP/IP options. For example, the documentation says that IP_MULTICAST_LOOP is a 4-byte option, but the IPMulticastPitch sample negotiates a size of 1 byte. What's the scoop?
A: In this case, the documentation is wrong. The following table enumerates all the TCP/IP options and their sizes.
|
XTI Level
|
XTI Name
|
Size
|
|
|
INET_IP
|
IP_ADD_MEMBERSHIP
|
sizeof(struct ip_mreq)
|
|
|
INET_IP
|
IP_BROADCAST
|
4
|
|
|
INET_IP
|
IP_BROADCAST_IFADDR
|
4
|
|
|
INET_IP
|
IP_DONTROUTE
|
4
|
|
|
INET_IP
|
IP_DROP_MEMBERSHIP
|
sizeof(struct ip_mreq)
|
|
|
INET_IP
|
IP_HDRINCL
|
4
|
|
|
INET_IP
|
IP_MULTICAST_IF
|
4
|
|
|
INET_IP
|
IP_MULTICAST_LOOP
|
1
|
*
|
|
INET_IP
|
IP_MULTICAST_TTL
|
1
|
|
|
INET_IP
|
IP_OPTIONS
|
<= 40
|
|
|
INET_IP
|
IP_RECVDSTADDR
|
4
|
|
|
INET_IP
|
IP_RECVIFADDR
|
4
|
|
|
INET_IP
|
IP_RECVOPTS
|
4
|
|
|
INET_IP
|
IP_REUSEADDR
|
4
|
|
|
INET_IP
|
IP_REUSEPORT
|
4
|
|
|
INET_IP
|
IP_TOS
|
1
|
|
|
INET_IP
|
IP_TTL
|
1
|
|
|
|
|
|
|
|
INET_TCP
|
TCP_ABORT_THRESHOLD
|
4
|
|
|
INET_TCP
|
TCP_CONN_ABORT_THRESHOLD
|
4
|
|
|
INET_TCP
|
TCP_CONN_NOTIFY_THRESHOLD
|
4
|
|
|
INET_TCP
|
TCP_KEEPALIVE
|
sizeof(struct t_kpalive)
|
*
|
|
INET_TCP
|
TCP_MAXSEG
|
4
|
|
|
INET_TCP
|
TCP_NODELAY
|
4
|
|
|
INET_TCP
|
TCP_NOTIFY_THRESHOLD
|
4
|
|
|
INET_TCP
|
TCP_OOBINLINE
|
4
|
|
|
INET_TCP
|
TCP_URGENT_PTR_TYPE
|
4
|
|
|
|
|
|
|
|
INET_UDP
|
UDP_CHECKSUM
|
4
|
|
|
INET_UDP
|
UDP_RX_ICMP
|
1
|
*
|
|
|
|
|
|
|
XTI_GENERIC
|
XTI_DEBUG
|
4
|
|
|
XTI_GENERIC
|
XTI_LINGER
|
sizeof(struct t_linger)
|
|
|
XTI_GENERIC
|
XTI_PROTOTYPE
|
4
|
|
|
XTI_GENERIC
|
XTI_RCVBUF
|
4
|
|
|
XTI_GENERIC
|
XTI_RCVLOWAT
|
4
|
|
|
XTI_GENERIC
|
XTI_SNDBUF
|
4
|
|
|
XTI_GENERIC
|
XTI_SNDLOWAT
|
4
|
|
|
Note:
The IP_REUSEPORT and IP_BROADCAST_IFADDR are not currently supported by Open Transport (as of version 2.0.3). They will be available in a future release of Open Transport.
|
-- Quinn "The Eskimo!"
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