1-4
Cisco ASA Series CLI Configuration Guide
Chapter 1 Configuring the Botnet Traffic Filter
Information About the Botnet Traffic Filter
When you add a domain name to the static database, the ASA waits 1 minute, and then sends a DNS
request for that domain name and adds the domain name/IP address pairing to the
DNS host cache
. (This
action is a background process, and does not affect your ability to continue configuring the ASA). We
recommend also enabling DNS packet inspection with Botnet Traffic Filter snooping. The ASA uses
Botnet Traffic Filter snooping instead of the regular DNS lookup to resolve static blacklist domain names
in the following circumstances:
•
The ASA DNS server is unavailable.
•
A connection is initiated during the 1 minute waiting period before the ASA sends the regular DNS
request.
If DNS snooping is used, when an infected host sends a DNS request for a name on the static database,
the ASA looks inside the DNS packets for the domain name and associated IP address and adds the name
and IP address to the DNS reverse lookup cache.
If you do not enable Botnet Traffic Filter snooping, and one of the above circumstances occurs, then that
traffic will not be monitored by the Botnet Traffic Filter.
Information About the DNS Reverse Lookup Cache and DNS Host Cache
When you use the dynamic database with DNS snooping, entries are added to the DNS reverse lookup
cache. If you use the static database, entries are added to the DNS host cache (see the
About the Static Database” section on page 1-3
about using the static database with DNS snooping and
the DNS reverse lookup cache).
Entries in the DNS reverse lookup cache and the DNS host cache have a time to live (TTL) value
provided by the DNS server. The largest TTL value allowed is 1 day (24 hours); if the DNS server
provides a larger TTL, it is truncated to 1 day maximum.
For the DNS reverse lookup cache, after an entry times out, the ASA renews the entry when an infected
host initiates a connection to a known address, and DNS snooping occurs.
For the DNS host cache, after an entry times out, the ASA periodically requests a refresh for the entry.
For the DNS host cache, the maximum number of blacklist entries and whitelist entries is 1000 each.
lists the maximum number of entries in the DNS reverse lookup cache per model.
Table 1-1
DNS Reverse Lookup Cache Entries per Model
ASA Model
Maximum Entries
ASA 5505
5000
ASA 5510
10,000
ASA 5520
20,000
ASA 5540
40,000
ASA 5550
40,000
ASA 5580
100,000
Summary of Contents for 5505 - ASA Firewall Edition Bundle
Page 28: ...Glossary GL 24 Cisco ASA Series CLI Configuration Guide ...
Page 61: ...P A R T 1 Getting Started with the ASA ...
Page 62: ......
Page 219: ...P A R T 2 Configuring High Availability and Scalability ...
Page 220: ......
Page 403: ...P A R T 2 Configuring Interfaces ...
Page 404: ......
Page 499: ...P A R T 2 Configuring Basic Settings ...
Page 500: ......
Page 533: ...P A R T 2 Configuring Objects and Access Lists ...
Page 534: ......
Page 601: ...P A R T 2 Configuring IP Routing ...
Page 602: ......
Page 745: ...P A R T 2 Configuring Network Address Translation ...
Page 746: ......
Page 845: ...P A R T 2 Configuring AAA Servers and the Local Database ...
Page 846: ......
Page 981: ...P A R T 2 Configuring Access Control ...
Page 982: ......
Page 1061: ...P A R T 2 Configuring Service Policies Using the Modular Policy Framework ...
Page 1062: ......
Page 1093: ...P A R T 2 Configuring Application Inspection ...
Page 1094: ......
Page 1191: ...P A R T 2 Configuring Unified Communications ...
Page 1192: ......
Page 1333: ...P A R T 2 Configuring Connection Settings and QoS ...
Page 1334: ......
Page 1379: ...P A R T 2 Configuring Advanced Network Protection ...
Page 1380: ......
Page 1475: ...P A R T 2 Configuring Modules ...
Page 1476: ......
Page 1549: ...P A R T 2 Configuring VPN ...
Page 1550: ......
Page 1965: ...P A R T 2 Configuring Logging SNMP and Smart Call Home ...
Page 1966: ......
Page 2059: ...P A R T 2 System Administration ...
Page 2060: ......
Page 2098: ...1 8 Cisco ASA Series CLI Configuration Guide Chapter 1 Troubleshooting Viewing the Coredump ...
Page 2099: ...P A R T 2 Reference ...
Page 2100: ......