From 1dbefbcfbbd355fe9472ec272738209252eb2bec Mon Sep 17 00:00:00 2001 From: Suzanne Goldlust Date: Thu, 23 Jul 2020 13:05:43 +0000 Subject: [PATCH] Update description of forwarding behavior in ARM (cherry picked from commit 30e126ad02c703e51e6df58ec1e84bdb72884426) --- doc/arm/Bv9ARM-book.xml | 41 +++++++++++++++++++++++++++++------------ 1 file changed, 29 insertions(+), 12 deletions(-) diff --git a/doc/arm/Bv9ARM-book.xml b/doc/arm/Bv9ARM-book.xml index 5ea7b9ff46..1da056516e 100644 --- a/doc/arm/Bv9ARM-book.xml +++ b/doc/arm/Bv9ARM-book.xml @@ -516,18 +516,35 @@ - There may be one or more forwarders, - and they are queried in turn until the list is exhausted or an - answer - is found. Forwarders are typically used when it is undesirable - for all the servers at a given site to interact directly with the - rest of - the Internet's servers. A typical scenario involves - internal DNS servers and an - Internet firewall. Servers unable - to pass packets through the firewall forward their requests to the server - that can, and that server queries the Internet DNS servers - on the internal servers' behalf. + Forwarders are typically used when an administrator does not + wish for all the servers at a given site to interact + directly with the rest of the Internet. For example, a + common scenario is when multiple internal DNS servers are + behind an Internet firewall. Servers behind the firewall + forward their requests to the server with external access, + which queries Internet DNS servers on the internal servers' + behalf. + + + + Another scenario (largely now superseded by Response Policy + Zones) is to send queries first to a custom server for RBL + processing before forwarding them to the wider Internet. + + + + There may be one or more forwarders in a given setup. The + order in which the forwarders are listed in + named.conf does not determine the + sequence in which they are queried; rather, + named uses the response times from + previous queries to select the server that is likely to + respond the most quickly. A server that has not yet been + queried is given an initial small random response time to + ensure that it is tried at least once. Dynamic adjustment of + the recorded response times ensures that all forwarders are + queried, even those with slower response times. This + permits changes in behavior based on server responsiveness.