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Cisco ASA Series CLI Configuration Guide
Chapter 1 Configuring the Transparent or Routed Firewall
Information About the Firewall Mode
MAC Address vs. Route Lookups
When the ASA runs in transparent mode, the outgoing interface of a packet is determined by performing
a MAC address lookup instead of a route lookup.
Route lookups, however, are necessary for the following traffic types:
•
Traffic originating on the ASA—For example, if your syslog server is located on a remote network,
you must use a static route so the ASA can reach that subnet.
•
Traffic that is at least one hop away from the ASA with NAT enabled—The ASA needs to perform
a route lookup to find the next hop gateway; you need to add a static route on the ASA for the real
host address.
•
Voice over IP (VoIP) and DNS traffic with inspection enabled, and the endpoint is at least one hop
away from the ASA—For example, if you use the transparent firewall between a CCM and an H.323
gateway, and there is a router between the transparent firewall and the H.323 gateway, then you need
to add a static route on the ASA for the H.323 gateway for successful call completion. If you enable
NAT for the inspected traffic, a static route is required to determine the egress interface for the real
host address that is embedded in the packet. Affected applications include:
–
CTIQBE
–
DNS
–
GTP
–
H.323
–
MGCP
–
RTSP
–
SIP
–
Skinny (SCCP)
ARP Inspection
By default, all ARP packets are allowed through the ASA. You can control the flow of ARP packets by
enabling ARP inspection.
When you enable ARP inspection, the ASA compares the MAC address, IP address, and source interface
in all ARP packets to static entries in the ARP table, and takes the following actions:
•
If the IP address, MAC address, and source interface match an ARP entry, the packet is passed
through.
•
If there is a mismatch between the MAC address, the IP address, or the interface, then the ASA drops
the packet.
•
If the ARP packet does not match any entries in the static ARP table, then you can set the ASA to
either forward the packet out all interfaces (flood), or to drop the packet.
Note
The dedicated management interface, if present, never floods packets even if this parameter
is set to flood.
ARP inspection prevents malicious users from impersonating other hosts or routers (known as ARP
spoofing). ARP spoofing can enable a “man-in-the-middle” attack. For example, a host sends an
ARP request to the gateway router; the gateway router responds with the gateway router MAC address.
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: ......