</TD><TD ALIGN="LEFT" VALIGN="TOP" WIDTH=586>for the DARPA-Internet family, the address is either a host name present in the host name data base, hosts, or a DARPA Internet address expressed in the Internet standard dot notation. For the Xerox Network SystemsTM family, addresses are net:a.b.c.d.e.f, where net is the assigned network number (in decimal), and each of the six bytes of the host number, a through f, are specified in hexadecimal. The host number may be omitted on 10Mb/s Ethernet interfaces, which use the hardware physical address, and on interfaces other than the first. For the ISO family, addresses are specified as a long hexadecimal string, as in the Xerox family. However, two consecutive dots imply a zero byte, and the dots are optional, if the user wishes to count out long strings of digits in network byte order.
</TD><TD ALIGN="LEFT" VALIGN="TOP" WIDTH=586>Specifies the address family which affects interpretation of the remaining parameters. Since an interface can receive transmissions in differing protocols with different naming schemes, specifying the address family is recommended. The address or protocol families currently supported are inet, iso, and ns.
</TD><TD ALIGN="LEFT" VALIGN="TOP" WIDTH=606>Establish an additional network address for this interface. This is sometimes useful when changing network numbers, and one wishes to accept packets addressed to the old interface.
</TD><TD ALIGN="LEFT" VALIGN="TOP" WIDTH=606>Enable the use of the Address Resolution Protocol in mapping between network level addresses and link level addresses (default). This is currently implemented for mapping between DARPA Internet addresses and 10Mb/s Ethernet addresses.
</TD><TD ALIGN="LEFT" VALIGN="TOP" WIDTH=606>Specify the address to use to represent broadcasts to the network. The default broadcast address is the address with a host part of all 1's.
</TD><TD ALIGN="LEFT" VALIGN="TOP" WIDTH=606>Remove the network address specified. This would be used if you incorrectly specified an alias, or it was no longer needed. If you have incorrectly set an NS address having the side effect of specifying the host portion, removing all NS addresses will allow you to respecify the host portion.
</TD><TD ALIGN="LEFT" VALIGN="TOP" WIDTH=606>Mark an interface `down'. When an interface is marked `down', the system will not attempt to transmit messages through that interface. If possible, the interface will be reset to disable reception as well. This action does not automatically disable routes using the interface.
</TD><TD ALIGN="LEFT" VALIGN="TOP" WIDTH=606>This is used to specify an Internet host which is willing to receive ip packets encapsulating NS packets bound for a remote network. An apparent point-to-point link is constructed, and the address specified will be taken as the NS address and network of the destination. IP encapsulation of CLNP packets is done differently.
</TD><TD ALIGN="LEFT" VALIGN="TOP" WIDTH=606>Set the routing metric of the interface to n, default 0. The routing metric is used by the routing protocol routed. Higher metrics have the effect of making a route less favourable; metrics are counted as addition hops to the destination network or host.
</TD><TD ALIGN="LEFT" VALIGN="TOP" WIDTH=606>Set the maximum transmission unit of the interface to n; the default is interface-specific. The mtu is used to limit the size of packets that are transmitted on an interface. Not all interfaces support setting the mtu, and some interfaces have range restrictions.
</TD><TD ALIGN="LEFT" VALIGN="TOP" WIDTH=606>(Inet and ISO) : specify how much of the address to reserve for subdividing networks into sub-networks. The mask includes the network part of the local address and the subnet part, which is taken from the host field of the address. The mask can be specified as a single hexadecimal number with a leading 0x, with a dot-notation Internet address, or with a pseudo-network name listed in the network table networks. The mask contains 1's for the bit positions in the 32-bit address which are to be used for the network and subnet parts, and 0's for the host part. The mask should contain at least the standard network portion, and the subnet field should be contiguous with the networkportion.
</TD><TD ALIGN="LEFT" VALIGN="TOP" WIDTH=606>This specifies a trailing number of bytes for a received NSAP used for local identification, the remaining leading part of which is taken to be the NET (Network Entity Title). The default value is 1, which is conformant to US GOSIP. When an ISO address is set in an IfConfig command, it is really the NSAP which is being specified. For example, in US GOSIP, 20 hex digits should be specified in the ISO NSAP to be assigned to the interface. There is some evidence that a number different from 1 may be useful for AFI 37 type addresses.
</TD><TD ALIGN="LEFT" VALIGN="TOP" WIDTH=606>Request the use of a `trailer' link level encapsulation when sending (default). If a network interface supports trailers, the system will, when possible, encapsulate outgoing messages in a manner which minimizes the number of memory to memory copy operations performed by the receiver. On networks that support the Address Resolution Protocol (see <A HREF="#arp">ARP</A>; currently, only 10 Mb/s Ethernet), this flag indicates that the system should request that other systems use trailers when sending to this host. Similarly, trailer encapsulations will be sent to other hosts that have made such requests. Currently used by Internet protocols only.
</TD><TD ALIGN="LEFT" VALIGN="TOP" WIDTH=606>Enable special processing of the link level of the interface. These three options are interface specific in actual effect, however, they are in general used to select special modes of operation. An example of this is to enable SLIP compression. Currently, only used by SLIP.
</TD><TD ALIGN="LEFT" VALIGN="TOP" WIDTH=606>Mark an interface `up'. This may be used to enable an interface after an IfConfig down. It happens automatically when setting the first address on an interface. If the interface was reset when previously marked down, the hardware will be re-initialized
</TD><TD ALIGN="LEFT" VALIGN="TOP" WIDTH=606>This displays information on all interfaces. When followed by a configuration parameter, it will also set the configuration on all interfaces.
</TD><TD ALIGN="LEFT" VALIGN="TOP" WIDTH=606>Similar to IfConfig -a, except it only affects interfaces that are currently marked as up. Conversely, IfConfig -ad affects only interfaces that are marked down. IfConfig displays the current configuration for a network interface when no optional parameters are supplied. If a protocol family is specified, IfConfig will report only the details specific to that protocol family. Only the super-user may modify the configuration of a network interface.
</TD><TD ALIGN="LEFT" VALIGN="TOP" WIDTH=595>wait within seconds between sending each packet. The default is to wait for one second between each packet. This option is incompatible with the -f option.
</TD><TD ALIGN="LEFT" VALIGN="TOP" WIDTH=595>if preload is specified, ping sends that many packets as fast as possible before falling into its normal mode of behaviour
</TD><TD ALIGN="LEFT" VALIGN="TOP" WIDTH=595>you may specify up to 16 `pad' bytes to fill out the packet you send. This is useful for diagnosing data-dependent problems in a network. For example -p ff will cause the sent packet to be filled with all ones.
</TD><TD ALIGN="LEFT" VALIGN="TOP" WIDTH=595>specifies the number of data bytes to be sent. The default is 56, which translate into 64 ICMP data bytes when combined with the 8 bytes of ICMP header data.
</TD></TR>
</TABLE>
<H2>Use </H2>
<P>
An Internet can be a large and complex aggregation of network
hardware, connected together by gateways. Tracking a single-point
hardware or software failure can be difficult. The Ping program
utilises the ICMP protocol's mandatory ECHO_REQUEST datagram to
elicit an ICMP ECHO_RESPONSE from a host or gateway. ECHO_REQUEST
datagrams (or pings have an IP and ICMP header, and then an arbitrary
number of padding bytes used to fill out the packet.
<P>
The optional -d parameter sets the SO_DEBUG option on the socket
being used. The optional -f parameter causes a flood ping. It
outputs packets as fast as they come back or one hundred times
per second, whichever is more. For every ECHO_REQUEST sent a period
`.' is printed, while for every ECHO_REPLY received a backspace
is printed. Providing a rapid display of the number of packets
dropped, but only a super-user may use this option and can be
hard on a network.
<P>
The optional -n parameter specifies numeric output only. No attempt
will be made to look up symbolic names for host addresses.
<P>
The optional -q parameter specifies quiet output. Nothing is displayed
except the summary lines at start-up time and when finished.
<P>
The optional -r parameter bypasses the normal routing tables and
sends directly to a host on an attached network. If the host is
not on a directly-attached network, an error is returned. This
option can be used to ping a local host through an interface that
has no route through it (e.g. after the interface was dropped
by routed).
<P>
The optional -v parameter specifies verbose output. ICMP packets
other than ECHO_RESPONSE that are received are listed. The optional
-R parameter specifies the recording of the route. Includes the
RECORD_ROUTE option in the ECHO_REQUEST packet and displays the
route buffer on returned packets. Note that the IP header is only
large enough for nine such routes. Many hosts ignore or discard
this option.
<P>
When using ping for fault isolation, it should first be run on
the local host, to verify that the local network interface is
up and running. Then, hosts and gateways further and further away
should be `pinged'.
<H3>ICMP packet details </H3>
<P>
An IP header without options is 20 bytes. An ICMP ECHO_REQUEST
packet contains an additional eight bytes worth of ICMP header
followed by some data. When a packetsize is given, this indicated
the size of this extra piece of data (default is 56). The amount
of data received inside of an IP packet of type ICMP ECHO_REPLY
will always be eight bytes more than the requested data space
(the ICMP header).
<P>
If the data space is at least eight bytes large, ping uses the
first eight bytes of this space to include a timestamp which it
uses in the computation of round trip times. If less than eight
bytes of pad are specified, no round trip times are given.
<H3>Duplicate and damaged packets </H3>
<P>
Ping will report duplicate and damaged packets. Duplicate packets
should never occur, and seem to be caused by inappropriate link-level
retransmissions. Duplicates may occur in many situations and are
rarely (if ever) a good sign, although the presence of low levels
of duplicates may not always be cause for alarm.
<P>
Damaged packets are obviously serious cause for alarm and often
indicate broken hardware somewhere in the ping packet's path (in
the network or in the hosts).
<H3>Trying different data patterns </H3>
<P>
The (inter)network layer should never treat packets differently
depending on the data contained in the data portion. However,
data-dependent problems can get into networks and remain undetected.
In many cases the pattern that will have problems is something
that doesn't have sufficient `transitions', such as all ones or
all zeros. It's not usually enough to specify a data pattern of
all zeros on the command line because the pattern of interest
is at the data link level, and the relationship between what you
type and what the controllers transmit can be complicated.
<P>
This means that if you have a data-dependent problem you will
probably have to do a lot of testing to find it. If you are lucky,
you may manage to find a file that either can't be sent across
your network or that takes longer to transfer than other similar
size files. Then test using -p option of Ping examine for file
</TD><TD ALIGN="LEFT" VALIGN="TOP" WIDTH=558>an Internet hot or network specified either by name (which must be present in the respective host or network name data base <InetDBase$Path>...) or by address (using the standard Internet dot notation)
