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     ng_cisco — Cisco HDLC protocol netgraph node type


     #include <sys/types.h>
     #include <netinet/in.h>
     #include <netgraph/ng_cisco.h>


     The cisco node type performs encapsulation and de-encapsulation of packets using the Cisco
     HDLC protocol.  This is a fairly simple protocol for the transmission of packets across high
     speed synchronous lines.  Each packet is prepended with an Ethertype, indicating the
     protocol.  There is also a “keep alive” and an “inquire” capability.

     The downstream hook should connect to the synchronous line.  On the other side of the node
     are the inet, inet6, atalk, and ipx hooks, which transmit and receive raw IP, IPv6,
     AppleTalk, and IPX packets, respectively.  Typically these hooks would connect to the
     corresponding hooks on an ng_iface(4) type node.

IP Configuration

     In order to function properly for IP traffic, the node must be informed of the local IP
     address and netmask setting.  This is because the protocol includes an “inquire” packet
     which we must be prepared to answer.  There are two ways to accomplish this, manually and

     Whenever such an inquire packet is received, the node sends a NGM_CISCO_GET_IPADDR control
     message to the peer node connected to the inet hook (if any).  If the peer responds, then
     that response is used.  This is the automatic method.

     If the peer does not respond, the node falls back on its cached value for the IP address and
     netmask.  This cached value can be set at any time with a NGM_CISCO_SET_IPADDR message, and
     this is the manual method.

     If the inet hook is connected to the inet hook of an ng_iface(4) node, as is usually the
     case, then configuration is automatic as the ng_iface(4) understands the
     NGM_CISCO_GET_IPADDR message.


     This node type supports the following hooks:

     downstream  The connection to the synchronous line.

     inet        IP hook.

     inet6       IPv6 hook.

     atalk       AppleTalk hook.

     ipx         IPX hook.


     This node type supports the generic control messages, plus the following:

     NGM_CISCO_SET_IPADDR (setipaddr)
          This command takes an array of two struct in_addr arguments.  The first is the IP
          address of the corresponding interface and the second is the netmask.

     NGM_CISCO_GET_IPADDR (getipaddr)
          This command returns the IP configuration in the same format used by
          NGM_CISCO_SET_IPADDR.  This command is also sent by this node type to the inet peer
          whenever an IP address inquiry packet is received.

     NGM_CISCO_GET_STATUS (getstats)
          Returns a struct ngciscostat:

              struct ngciscostat {
                uint32_t   seqRetries;        /* # unack'd retries */
                uint32_t   keepAlivePeriod;   /* in seconds */


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


     netgraph(4), ng_iface(4), ngctl(8)

     D. Perkins, Requirements for an Internet Standard Point-to-Point Protocol, RFC 1547.


     Cisco is a trademark of Cisco Systems, Inc.


     The ng_cisco node type was implemented in FreeBSD 4.0.


     Julian Elischer <>
     Archie Cobbs <>


     Not all of the functionality has been implemented.  For example, the node does not support
     querying the remote end for its IP address and netmask.