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
inetinet6atalk
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_iface4
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 automatically.
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_iface4
node, as is usually the case, then configuration is automatic as the
ng_iface4
understands the
NGM_CISCO_GET_IPADDR
message.
HOOKS
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
CONTROL MESSAGES
This node type supports the generic control messages, plus the following:
NGM_CISCO_SET_IPADDR
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
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.
