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Catalyst 4500 Series Switch, Cisco IOS Software Configuration Guide - Cisco IOS XE 3.9.xE and IOS 15.2(5)Ex
 
Chapter 45      Configuring AVC with DNS-AS
About AVC with DNS-AS
Figure 45-1 AVC with DNS-AS Process Flow
High Availability and ISSU for AVC with DNS-AS
The AVC with DNS-AS feature supports High Availability and ISSU. 
For High Availability, the binding table database of the active DNS-AS client is synchronized with the 
standby DNS-AS client. As long as AVC with DNS-AS is enabled, no additional user configuration is 
required. 
The binding table entries are synchronized when:
• The standby comes up (bulk synchronization).
• New entries are added to the binding table database.
• One or more entries are cleared from the database.
Note AVC with DNS-AS is also supported in the VSS mode, and Quad-Supervisor VSS Mode. 
1 Host 3 Authoritative DNS Server
2DNS-AS Client
An “A” record request from 
the host to the DNS server
An “A” record response from the 
DNS server to the host
A copy of the host’s “A” 
record request that the 
DNS-AS client saves
——
TXT record and “A” record 
request from the DNS-AS 
client to the DNS server
TXT record and “A” record 
response from the DNS server to 
the DNS-AS client