NG_ONE2MANY(4) FreeBSD Kernel Interfaces Manual NG_ONE2MANY(4)


ng_one2manypacket multiplexing netgraph node type


#include < sys/types.h>
#include < netgraph/ng_one2many.h>


The one2many provides a simple mechanism for routing packets over several links in a one-to-many (and in the reverse direction, many-to-one) fashion. There is a single hook named one, and multiple hooks named many0, many1, etc. Packets received on any of the many hooks are forwarded out the one hook. Packets received on the one hook are forwarded out one or more of the many hooks; which hook(s) is determined by the node's configured transmit algorithm. Packets are not altered in any way.

Each of the connected many links may be considered to be up or down. Packets are never delivered out a many hook that is down. How a link is determined to be up or down depends on the node's configured link failure detection algorithm.

Before an interface or link can be plumbed into a group, its status must be marked as being “up”. This is normally setup during the initial boot stages by rc.conf(5). It is also possible to change an interface's status to “up” by using the ifconfig(8) utility.


Packets are delivered out the many hooks in sequential order. Each packet goes out on a different many hook.
Packets are delivered out all the many hooks. Each packet goes out each many hook.
Packets are delivered out the first active many hook.

In the future other algorithms may be added as well.


The node distinguishes between active and failed links. Data is sent only to active links. The following link failure detection algorithms are available:
The node is explicitly told which of the links are up via the NGM_ONE2MANY_SET_CONFIG control message (see below). Newly connected links are down until configured otherwise.
The node listens to flow control message from many hooks, and considers link failed if NGM_LINK_IS_DOWN is received. If the NGM_LINK_IS_UP message is received, node considers link active.

In the future other algorithms may be added as well.

When all links are considered failed, node sends the NGM_LINK_IS_DOWN message towards the one hook. When at least one link comes up, node sends the NGM_LINK_IS_UP message towards the one hook.


This node type supports up to NG_ONE2MANY_MAX_LINKS hooks named many0, many1, etc., plus a single hook named one.


This node type supports the generic control messages, plus the following:
Sets the node configuration using a struct ng_one2many_link_config as the control message argument:

/* Node configuration structure */ 
struct ng_one2many_config { 
  uint32_t    xmitAlg;        /* how to distribute packets */ 
  uint32_t    failAlg;        /* how to detect link failure */ 
  u_char      enabledLinks[NG_ONE2MANY_MAX_LINKS]; 

Currently, the valid settings for the xmitAlg field are NG_ONE2MANY_XMIT_ROUNDROBIN (default) or NG_ONE2MANY_XMIT_ALL. The valid settings for failAlg are NG_ONE2MANY_FAIL_MANUAL (default) or NG_ONE2MANY_FAIL_NOTIFY.

Returns the current node configuration in a struct ng_one2many_link_config.
This command takes a 32 bit link number as an argument and returns a struct ng_one2many_link_stats containing statistics for the corresponding many link, which may or may not be currently connected:

/* Statistics structure (one for each link) */ 
struct ng_one2many_link_stats { 
  uint64_t   recvOctets;     /* total octets rec'd on link */ 
  uint64_t   recvPackets;    /* total pkts rec'd on link */ 
  uint64_t   xmitOctets;     /* total octets xmit'd on link */ 
  uint64_t   xmitPackets;    /* total pkts xmit'd on link */ 
  uint64_t   memoryFailures; /* times couldn't get mem or mbuf */ 

To access statistics for the one link, use the link number -1.

This command takes a 32 bit link number as an argument and clears the statistics for that link.
Same as NGM_ONE2MANY_GET_STATS, but also atomically clears the statistics for the link as well.


This node shuts down upon receipt of a NGM_SHUTDOWN control message, or when all hooks have been disconnected.


The following commands will set up Ethernet interfaces fxp0 to deliver packets alternating over the physical interfaces corresponding to networking interfaces fxp0 through fxp3:

  # Plumb nodes together 
  ngctl mkpeer fxp0: one2many upper one 
  ngctl connect fxp0: fxp0:upper lower many0 
  ngctl connect fxp1: fxp0:upper lower many1 
  ngctl connect fxp2: fxp0:upper lower many2 
  ngctl connect fxp3: fxp0:upper lower many3 
  # Allow fxp1 through fxp3 to xmit/recv fxp0 frames 
  ngctl msg fxp1: setpromisc 1 
  ngctl msg fxp2: setpromisc 1 
  ngctl msg fxp3: setpromisc 1 
  ngctl msg fxp1: setautosrc 0 
  ngctl msg fxp2: setautosrc 0 
  ngctl msg fxp3: setautosrc 0 
  # Configure all four links as up 
  ngctl msg fxp0:upper \ 
    setconfig "{ xmitAlg=1 failAlg=1 enabledLinks=[ 1 1 1 1 ] }" 
  # Bring up interface 
  ifconfig fxp0 netmask 0xfffffffc

With a similar setup on a peer machine (using the address, a point-to-point Ethernet connection with four times normal bandwidth is achieved.


The ng_one2many node type was implemented in FreeBSD 4.2.


The one2many netgraph node (with round-robin algorithm) was written by Archie Cobbs <archie@FreeBSD.org>. The all algorithm was added by Rogier R. Mulhuijzen <drwilco@drwilco.net>.


More transmit and link failure algorithms should be supported. A good candidate is Cisco's Etherchannel.
November 13, 2012 FreeBSD