TCP/IP Network Characteristics 7-15
Configuring Domain Name System (DNS) Characteristics
If the access server cannot reach a learned name server because of gateway restrictions
outside the server, it does not flag the unreachable name server. This can often cause
name resolution to time out and fail. In this configuration use either the STUB or
SLAVE name resolution mode.
Assigning DNS Server Addresses Automatically
The DNS autoconfigure feature on the access server allows dial-up clients to receive
DNS configuration information automatically from the access server when
establishing a remote PPP connection.
The access server assigns a primary and secondary DNS server to the remote PPP
client. The access server uses an algorithm to obtain the addresses of the DNS servers
from its database.
The access server assigns only local name servers to PPP clients. It makes two passes
through a list of local nameservers. The following table describes how the access
server determines which name servers to assign to the PPP client:
Pass Description
1a)
The access server goes through a list of learned name servers
and searches for name servers that are on its network (by using
the access server’s subnet mask) and have a positive time to live
(ttl).
b)
The access server goes through a list of locally-configured
name servers and searches for name servers that are on its
network (by using the access server’s subnet mask) and have a
positive time to live (ttl).
c)
The access server assigns the first valid name server as the
Primary Nameserver and the second valid name server as the
Secondary Nameserver.
2
If the access server does not find two valid name servers:
a)
The access server goes through the list of learned name servers
and searches for name servers with a positive time to live (ttl).
b)
The access server goes through the list of locally-configured
name servers and searches for name servers with a positive time
to live (ttl).
c)
The access server assigns the first valid name server as the
Primary Nameserver and the second valid name server as the
Secondary Nameserver.
