DEC Digital Alpha VME 4/224 User Manual page 318

boot
EWA0_DEF_SINETADDR
EWA0_DEF_GINETADDR
EWA0_DEF_SUBNETMASK
EWA0_DEF_INETFILE
These variables are defined in the following example:
>>> set EWA0_DEF_INETADDR 16.123.16.53
>>> set EWA0_DEF_SINETADDR 16.123.16.242
>>> set EWA0_DEF_GINETADDR 16.123.16.242
>>> set EWA0_DEF_SUBNETMASK 255.255.255.0
>>> set EWA0_DEF_INETFILE bootfiles/vmunix
>>> set EWA0_INET_INIT nvram
Another way for the database to be initialized is when BOOTP is invoked,
either explicitly or as a consequence of invoking TFTP. In the usual case,
BOOTP copies the received reply packet into the database, initializing it.
However, if the nobroadcast argument is specified, that is,
/ewa0 , no request is broadcast, no reply can be received, and so nothing is
copied into the database.
The BOOTP database is initialized every time a BOOTP/TFTP boot is performed.
Whether the database is initialized from the response to a BOOTP broadcast or
from the NVRAM environment variables depends on whether the EWA0_INET_
INIT environment variable is set to BOOTP or NVRAM, respectively.
TFTP, BOOTP, and ARP all use retransmission to improve robustness. If
an initial transmission is not answered appropriately, the protocol software
retransmits. Each protocol has an environment variable to control the number
of retries. The variables are named EWA0_ARP_TRIES, EWA0_BOOTP_TRIES,
and EWA0_TFTP_TRIES. The default value of these is 3. If the value of one of
these variables is less than 1, the protocol fails immediately. Machines located
on very busy networks or associated with heavily-loaded servers may need these
variables set higher.
Three retries translates to an average of 12 seconds before failing. The
retransmission algorithms use a randomized exponential backoff delay. If the
first try fails, a second try occurs about 4 seconds later. A third try occurs after
another 8 seconds, a fourth after 16 seconds, and so on, up to 64 seconds. These
times are averages since random jitter of about +/- 50% is added to each delay.
For example, if EWA0_ARP_TRIES is set to 3, ARP fails if it does not get a
response within 12 seconds on average; the actual timeout is between 6 and 18
seconds.
13–10 Console Commands
bootp:nobroadcast