Janus TCP/IP Base V7.8 changes: Difference between revisions
mNo edit summary |
mNo edit summary |
||
| Line 4: | Line 4: | ||
==DNS Retries== | ==DNS Retries== | ||
Prior to Sirmods Version 7.8, | Prior to Sirmods Version 7.8, | ||
the JANUS NAMESERVER command had no facility to call for a retry of | the [[JANUS NAMESERVER]] command had no facility to call for a retry of | ||
a DNS UDP packet for which no response is received. | a DNS UDP packet for which no response is received. | ||
This meant that if Janus does a DNS lookup just when the target nameserver | This meant that if Janus does a DNS lookup just when the target nameserver | ||
| Line 13: | Line 13: | ||
The version 7.8 DNS Retries feature is | The version 7.8 DNS Retries feature is | ||
a RETRIES parameter for the JANUS NAMESERVER command. | a RETRIES parameter for the JANUS NAMESERVER command. | ||
Setting RETRIES to a positive integer value, say 2, instructs Janus | |||
to retry as many as two times if no response was received to a DNS lookup. | |||
Setting RETRIES to 0, its default, means no retries are attempted. | |||
On a swamped network, it is probably better to | |||
set a JANUS NAMESERVER TIMEOUT value of, say, 3 and a RETRIES setting of 2, rather than to set TIMEOUT to | |||
10 with RETRIES 0. This is so because: | |||
*If a packet gets dropped, there is no benefit to waiting 10 seconds instead of 3. | |||
*It is very unlikely that it would take a nameserver 3 seconds to respond to a received request (including packet turnaround time). | |||
It probably does not make sense to set RETRIES | |||
to a value greater than 2: if packets are being dropped so frequently | |||
that three consecutive DNS requests are dropped, you have problems much more serious than the failed lookups. | |||
{{Hierarchy footer}} | {{Hierarchy footer}} | ||
Revision as of 04:43, 10 December 2010
{{#hierarchy-top:}} The following features are new or changed in Janus TCP/IP Base.
DNS Retries
Prior to Sirmods Version 7.8, the JANUS NAMESERVER command had no facility to call for a retry of a DNS UDP packet for which no response is received. This meant that if Janus does a DNS lookup just when the target nameserver is down for an instant, or if the UDP packet gets lost on the network (IP networks don't have to guarantee delivery of IP packets), the DNS lookup could fail.
The version 7.8 DNS Retries feature is a RETRIES parameter for the JANUS NAMESERVER command. Setting RETRIES to a positive integer value, say 2, instructs Janus to retry as many as two times if no response was received to a DNS lookup. Setting RETRIES to 0, its default, means no retries are attempted.
On a swamped network, it is probably better to set a JANUS NAMESERVER TIMEOUT value of, say, 3 and a RETRIES setting of 2, rather than to set TIMEOUT to 10 with RETRIES 0. This is so because:
- If a packet gets dropped, there is no benefit to waiting 10 seconds instead of 3.
- It is very unlikely that it would take a nameserver 3 seconds to respond to a received request (including packet turnaround time).
It probably does not make sense to set RETRIES to a value greater than 2: if packets are being dropped so frequently that three consecutive DNS requests are dropped, you have problems much more serious than the failed lookups.
{{#hierarchy-bottom:}}