IF_ATM(7M)IF_ATM(7M)NAMEif_atm - RFC 1577 compliant TCP/IP driver for SGI ATM interfaces.
DESCRIPTION
This software driver implements RFC 1577 (Classical IP and ARP over ATM).
This software driver creates ATM "virtual interfaces" that allow TCP/IP
networking across ATM switched and permanent virtual circuits. A virtual
interface is needed for every logical IP sub-net (LIS) in the ATM network
with which the system needs to communicate.
The number of virtual interfaces at system start-up is controlled by the
value assigned in ifatm_n_ifnets in the if_atm master file in the
/var/sysgen/master.d directory.
Each virtual interface has a default Maximum Transmission Unit (MTU) of
9180 bytes (per RFC 1577). However, this default can be overridden by
changing the value assigned in ifatm_mtusize in the if_atm master file in
the /var/sysgen/master.d directory. A value of zero in ifatm_mtusize will
cause the default MTU to be used.
The SN0 Quad OC-3c (XIO) and Challenge OC-3c boards support on-board TCP
& UDP checksuming. To enable or disable this feature, different values
can be assigned to ifatm_cksum in the if_atm master file in the
/var/sysgen/master.d directory. A value of zero (0) disables on-board
checksums. A value of one (1) causes the board to compute checksums on
received frames but not on transmitted frames. A value of two (2) causes
the board to compute checksums on transmitted frames but not on received
frames. A value of three (3) causes the board to compute checksums for
both transmitted and received frames.
To attach a virtual interface to an RFC 1577 LIS, the virtual interface
must be bound to a physical ATM port and configured with the ATM address
of the ATM ARP server for the LIS. These parameters are put in the
/var/atm/ifatm.conf configuration file or manually configured using
ifatmconfig(1m). These parameters must be specified before the interface
is brought ``UP'' using ifconfig(1m). Usually the parameters are put file
so that the system is properly configured when it is powered up.
Alternatively, permanent virtual circuits (PVCs) can be used for TCP/IP
communication. IP addresses are bound to PVCs by placing entries in the
/var/atm/pvc.conf configuration file. Each entry maps an IP address to a
specific port, VPI, and VCI. A daemon created by the atmarp(1m) command
reads this configuration file, creates the PVCs, and binds the IP
addresses to the PVCs. See atmarp(1m) for a description of this
configuration file.
The value of atm_special should always be set to zero (0). This variable
is reserved for SGI development use only.
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IF_ATM(7M)IF_ATM(7M)
When using switched virtual circuits (SVCs), before a packet can be sent
to a remote host, address resolution (ATMARP) must first take place.
Address resolution involves contacting the ATMARP server and requesting
the server provide the ATM address for the remote host, given the remote
host's IP address. Once the ATM address is known, a virtual circuit must
be established between the local and remote hosts so that IP packets can
flow between them. While this process is taking place, the kernel queues
(holds on to) the packet, so that once the virtual circuit is
established, the packet can then be sent. Because some ATM networks can
experience long delays during this process, a queue length of one (1)
(holding onto one packet) is sometimes not enough. It is possible that
the second packet is passed down to the ATM driver before the first
packet has had a chance to be transmitted. In this case, the first packet
is dropped and the second is queued. If the dropping of packets during
address resolution and circuit establishment is a problem, the queue
length (the number of packets that are held) can be changed by changing
the atmarp_qlen variable in the if_atm master file in the
/var/sysgen/master.d directory to a value greater than one (1).
FILES
/usr/include/sys/if_atm.h
/var/sysgen/master.d/if_atm
/var/atm/ifatm.conf
/var/atm/pvc.conf
SEE ALSOatm(7M), atmarp(1M), atmconfig(1M), ifatmconfig(1M), ifconfig(1M)
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