[Xorp-cvs] XORP cvs commit: xorp/fea

[Pavlin Radoslavov]

CVSROOT:	/usr/local/share/doc/apache/cvs
Module name:	xorp
Changes by:	pavlin at xorpc.icir.org	2006-10-06 20:55:21 UTC

XORP CVS repository


Modified files:
	fea           mfea_proto_comm.cc mfea_proto_comm.hh rawsock.cc 
	              rawsock.hh 

Log message:
	* Fix the mechanism for transmitting IPv4 packets, so now we can
	  transmit packets on Linux even if the source address doesn't belong
	  to the router. The problem with Linux is the following.
	
	  In case of Linux IP_HDRINCL IP packets are not fragmented and
	  are limited to the interface MTU. The raw(7) Linux manual is wrong
	  by saying it is a limitation only in Linux 2.2. It is a limitation
	  in 2.4 and 2.6 and there is no indication this is going to be fixed
	  in the future.
	  Hence, in case of Linux we do the following:
	    - If the IP packet fits in the MTU, then send the packet using
	      IP_HDRINCL option.
	    - Otherwise, if the IP source address belongs to the outgoing
	      interface, then use various socket options to specify some of
	      the IP header options.
	    - Otherwise, use IP_HDRINCL and fragment the IP packet in user
	      space before transmitting it. Note that in this case we need
	      to manage the ip_id field in the IP header.
	
	  The reasoning behind the above logic is: (1) If the IP source
	  address doesn't belong to one of the router's IP addresses, then
	  we must use IP_HDRINCL; (2) We want to avoid as much as possible
	  user-level IP packet fragmentation, because managing the ip_id
	  field in user space does not guarantee the same ip_id is reused
	  by the kernel as well (for the same tuple of <src, dest, protocol>).
	
	  Note that in case of all other OS-es we always use the IP_HDRINCL
	  option to transmit the packets.
	
	* Remove extra buffers for sending and receiving raw packets.
	  This reduces the run-time memory usage by 128KB.
	
	* Declare the IPv4 router alert option as static, and compute its
	  value on startup.
	
	* Minor cleanup.

Revision  Changes                                   Path
1.65      +197 -110;  commitid: 100a04526c1527ea6;  xorp/fea/mfea_proto_comm.cc
1.22      +7 -10;  commitid: 100a04526c1527ea6;     xorp/fea/mfea_proto_comm.hh
1.34      +211 -115;  commitid: 100a04526c1527ea6;  xorp/fea/rawsock.cc
1.10      +6 -9;  commitid: 100a04526c1527ea6;      xorp/fea/rawsock.hh