Chapter 11: Proxy Dns - Avaya 1000 Series Configuration Manual

Chapter 11: Proxy DNS

The Secure Router 1000 Series and 3120 provide support for Proxy DNS. Proxy DNS receives a request
from a host, resolves the domain name through communication with the DNS server, and sends the
response to the host. Proxy DNS is disabled by default.
Without Proxy DNS, if a master link connected to an ISP-based DNS server went down, DNS queries
could not be resolved. The solution to this issue would have been to change the DNS server IP address
to the address of a backup link. Even though a Windows-based PC host can be configured with up to 10
DNS server entries, it is often not feasible to configure this many DNS servers on every available host.
With the addition of Proxy DNS, the solution becomes much more simple.
Proxy DNS functions in such a way that it receives a request from a client and sends a response back.
The DNS server is specified as the interface address connecting the PC to the router. Using Proxy DNS,
clients do not need to worry about an ISP link or an exact DNS server, as the Proxy DNS feature handles
these. In the case of a host, all that is required is configuration of the interface address of the router as
the DNS server address.
The Proxy DNS feature supports multiple static (2) or dynamic (4) DNS server entries, of which any static
entries have higher precedence. Dynamic entries can be added to the list of DNS servers by DHCP &
PPPoE modules during registration of the module and can be removed when unregistered. When a client
makes a request to Proxy DNS for the address of a particular domain name, Proxy DNS contacts a list of
DNS servers in succession to resolve the domain name. When the domain has been resolved to an IP
address, the entry is added to the cache and also sent to the requesting client. When a DNS response is
received from the DNS server it is stored in the cache for the length of time specified by the TTL received for
the particular name. The cache supports up to 80 entries. If a client queries for a previously cached domain,
Proxy DNS responds with the cached entry. Removing the need to contact the DNS server for this entry
reduces traffic. When the cache table reaches its 80 entry capacity older dynamic cache entries are
removed to accommodate the new entries.
The DNS client will remain functioning as it did previously, as long as a primary and secondary name
server exists.
Configuring Proxy DNS
Use the following procedure to manually configure the proxy DNS feature to cache an address.
Procedure steps
1. 1 To configure proxy DNS, enter Configuration Mode.
configure terminal
2. Enter the ip sub-tree
ip
3. Ensure a DNS server has been configured.
Avaya Secure Router 1000 Series Configuration Guide December 2010 55