spansd(1M)spansd(1M)NAMEspansd - SPANS signalling daemon for ATM switched virtual circuits
SYNOPSIS
/usr/etc/spansd
[ -p tens_of_seconds ]
[ -c tens_of_seconds ]
[ -d debug_level ]
[ -l log_file ]
[ -l status_file ]
[ -g load_balance_group ]
DESCRIPTION
The spansd is a daemon which works in conjunction with the atm driver to
set up and tear down switched virtual circuits (SVC's) over ATM (Note:
spansd is only available on Origin 2000 systems). The daemon supports a
subset of the SPANS (Simple Protocol for ATM Network protocol. SPANS is a
signaling protocol that was designed at FORE Systems prior to the
existance of standard ATM signaling protocols.
To understand how the SPANS protocol works, a brief explanation is given.
However, for a more detailed description of the protocol, refer to FORE
Systems documentation.
When using the SPANS protocol, two virtual circuits are used to perform
the required tasks. By default, these are virtual circuits VCI 14 and VCI
15. VCI 15 carries the SPANS messages themselves, and VCI 14 carries
address resolution (ARP) messages. VCI's 32 through 255 are used for IP
packets.
When an ATM interface on a host is first configured up, it does not know
it's own ATM address. It must discover it's address from the network, or
more specifically, from the ATM switch. The switch periodically issues
SPANS status indication messages on all of it's ports where SPANS is
configured to run. These messages contain the ATM address of the switch,
the ATM address of the host and an epoch field. The epoch field is used
by the host to determine when the switch has been rebooted. Upon receipt
of these SPANS status indication messages, the host must respond with a
SPANS status response message. The status response message contains the
ATM address of the host (actually echoed from the request message) and an
epoch field. The epoch field is used by the switch to determine when the
host has been rebooted. All of the above messages flow on VCI 15. Once
the first exchange of status indication and status response messages
takes place between the host and switch, they can then move to the next
level of communication, which is address resolution.
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In order to send IP packets between hosts, each host must know the ATM
address of the remote host. To resolve this IP to ATM address mapping,
the hosts send ARP (Address Resolution Protocol) messages to each other
over VCI 14. Since ATM, by nature, is not a broadcast medium, the ATM
switch must emulate a broadcast by sending all packets that it receives
on VCI 14 to all the ports on the switch. By doing so, the ARP messages
can flow between hosts on the network, and address resolution can occur
much like it does on an Ethernet LAN. Once the IP to ATM address mapping
is known, a virtual circuit must be established between the two hosts
that can carry IP packets. To establish these virtual circuits, SPANS
open messages are sent over VCI 15. Once the virtual circuit is
established, the entry in the kernel ARP cache is updated and IP packets
can flow. When the virtual circuit needs to be torn down, SPANS close
messages are sent over VCI 15.
From the time address resolution begins until it completes, the entries
in the ARP cache are marked as "pending". Once address resolution
finishes successfully, the entries are marked as "complete". The SPANS
daemon keeps track of all of the pending and complete entries in the ARP
cache and flushes each of them periodically. Flushing of an entry in the
ARP cache includes closing of the virtual circuit associated with that
entry. If entries are pending for a period of time without becomming
complete, they are flushed. Once complete, the entries are also only
allowed to stay cached for a fixed amount of time before they are
flushed. Complete entries will only be flushed if they have been idle for
a certain amount of time.
Note that when running SPANS signaling protocol, IP packet encapsulation
does not use 802.2 LLC SNAP, but instead is uses NULL encapsulation (also
referred to as Fore IP ).
LOAD BALANCE GROUPS
A feature that allows load balancing of connections over multiple
interfaces is supported by the SPANS daemon. When this feature is being
used, multiple ATM interfaces on the same host are all configured to have
the same IP address. Hence, they all belong to the same IP subnet. As ARP
requests arrive at the host, connections are balanced (or round robined)
across all members of the load balance group.
SIGNALS
To control the behavior of the SPANS daemon, certain signals can be sent
to it using the "kill" command. Listed here are the signals that can be
sent.
SIGTERM Clean up and exit.
SIGUSR1 Write group, switch and metric information out to the
status file. Also, dump the ARP table entries to the
status file.
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SIGUSR2 Restart all the interfaces.
SIGWINCH Change the current debug level to zero.
SIGURG Change the current debug level to one.
SIGPOLL Change the current debug level to two.
CONFIGURATION
There are some configuration parameters of the SPANS daemon that can be
modified when the daemon is started. If not modified, a default
configuration takes affect. The following describes the parameters that
can be modified.
-p tens of seconds
This option allows the setting of the "pending entry"
timer. The value entered is in tens of seconds. The
default value for this is 1 (10 seconds).
-c tens of seconds
This option allows the setting of the "complete entry"
timer. The value entered is in tens of seconds. The
default value for this is 60 (600 seconds or 10 minutes).
-d debug level This option allows the setting of the debug level of the
SPANS daemon. A value of zero is no debug. The higher the
value, the more verbose debug output. The debug output is
written to the log file (see below). The default value for
this is zero.
-d log filename
This option allows the setting of the log file. The SPANS
daemon uses the log file to write informational, warning
and error messages as well as debug messages if debug is
enabled. The default value for this is "/tmp/spansd.log".
-d status filename
This option allows the setting of the status filename. The
default value for this is "/tmp/spansd.status".
-g load balance group
This option allows the setting of the load balance group.
The format of the option is a colon separated list of
interface ordinals. For example, "-g 0:1:2:3" tells the
host to consider ATM interfaces 0, 1, 2, and 3 to be part
of the same load balance group. By default, no interfaces
are a member of any load balance group.
CONFIGURATION FILE
Even though it can be started by entering a command on the command line,
typically, the SPANS daemon is started automatically at system boot time
by the /etc/init.d/atm script. To configure the SPANS daemon, for
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automatic startup, the file /var/atm/spansd.conf is used. A template of
this file should exist on systems that have SPANS installed. Simply enter
the options as if they were being entered on the command line, except
preceed them with the string "opts=", beginning in column 1.
CAVEATS
The SPANS daemon does NOT support Multicast or Multi-Point-to-Point (MPP)
channels.
The FORE ATM switch must be configured to run SPANS signaling on VCI 15.
This IS the default setting in the ATM switch.
The FORE ATM switch must be configured to run SPANS connectionless on VCI
14. This IS the default setting in the ATM switch.
The FORE ATM switch must be configured to run SPANS over AAL 5. This IS
NOT the default setting in the ATM switch.
The FORE ATM switch must be configured to use a maximum of 255 VCI's.
This IS NOT the default setting in the ATM switch.
The SPANS daemon does not support host-to-host connections. There must
always be an ATM switch connecting the hosts together.
The SPANS daemon is only supported on Quad OC-3c XIO ATM hardware.
The "pending entry" and "complete entry" timers are implemented as two
separate asynchronous timers. One timer is running in the kernel and has
an interval of one minute. The other timer is running in the SPANS daemon
and has an interval of ten seconds. Because of their asynchronous nature,
these timers can be off by as much as +/- one interval. For the "pending
entry" timeout, this means that a timeout can occur +/- ten seconds from
the specified timeout value. For the "complete entry" timeout, this means
that a timeout on an "idle complete entry" can occur +/- one minute and
ten seconds from the specified timeout value.
FILES
/usr/etc/spansd
/var/atm/ifatm.conf
/var/atm/spansd.conf
/tmp/spansd.log
/tmp/spansd.status
SEE ALSOatm(7M), if_atmarp(7M), atmarp(1M), atmconfig(1M), ifatmconfig(1M),
signal(2), kill(1)
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