Axel AX3000 80, User Manual

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Appendix
194
AX3000 Models 80 and 85 - User's Manual
- Whether the name to resolve is complete.
If no default DNS domain is defined in the AX3000 Set-Up, the resolution is done with the name
itself regardless of whether the name is full or not.
If one or more default DNS domains are defined, the resolution strategy depends on the name:
- Full name: the resolution is first done with this name. If unsuccessful new resolutions are
performed by concatenating the full name with the defined DNS domains.
- Incomplete Name: the resolutions are first done with the defined default DNS domains. If
unsuccessful a new resolution is performed with this incomplete name.
Example of name resolutions : looking at the host table in Chapter 3.1.3 the name resolution
attempts are:
- as400 : this is not a full name, the resolution is first made with the first DNS domain
(as400.servers.axel.com). Then, in event of failure, with the second DNS domain
(as400.terminals.axel.com). Then, in event of failure, the resolution is made with the name
itself (as400).
- linux : an IP address is associated. No DNS resolution.
- www.axel.com : this is a full name. The resolution is first made with the name itself
(www.axel.com). Then, in event of failure, the resolution is made with the first DNS domain
(www.axel.com.servers.axel.com). Then, in event of failure, with the second DNS domain
(www.axel.com.terminals.axel.com).
b) Resolution Method
To resolve a name, the AX3000 sends DNS requests to the DNS server(s).
If a DNS server sends back a positive response, then the IP address is found and the resolution
operation is completed. If not two cases of failure are possible:
- Receiving a negative response : the name is not known by this DNS server. The AX3000
will retry with a new DNS request or with the second DNS server.
- No response (time-out) : after a few seconds the DNS server has not sent back a response.
The AX3000 resends the same request to the DNS server.
Note : after 4 time-out errors on the same DNS server, this server is "removed" from the
resolution operation.
Note : if a response previously considered as a time-out error is received, this response is treated
as a valid response (positive or negative).
The AX3000 requests a recursive search to the DNS servers (and not iterative search). This
means that the DNS server must search itself for a DNS server which is able to resolve the
required name.
The resolution operation depends on the number of DNS servers. These are the steps for a one-
server resolution and a two-server resolution.
One DNS Server :
1 - A DNS request is sent to the server.
2 - In event of no response, this request is sent again (4 times max.).
3 - In event of negative answer, the resolution is aborted.
4 - If other requests can be sent (default DNS domains are defined), go back to step 1.
Two DNS Servers :
1 - A DNS request is sent to the server 1.