Cisco ASA Series Cli Configuration Manual page 141

Chapter 1 Configuring the Transparent or Routed Firewall
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Allowed MAC Addresses
The following destination MAC addresses are allowed through the transparent firewall. Any
MAC address not on this list is dropped.
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Passing Traffic Not Allowed in Routed Mode
In routed mode, some types of traffic cannot pass through the ASA even if you allow it in an access list.
The transparent firewall, however, can allow almost any traffic through using either an extended access
list (for IP traffic) or an EtherType access list (for non-IP traffic).
Non-IP traffic (for example AppleTalk, IPX, BPDUs, and MPLS) can be configured to go through using
an EtherType access list.
Note
The transparent mode ASA does not pass CDP packets packets, or any packets that do not have a valid
EtherType greater than or equal to 0x600. An exception is made for BPDUs and IS-IS, which are
supported.
Passing Traffic For Routed-Mode Features
For features that are not directly supported on the transparent firewall, you can allow traffic to pass
through so that upstream and downstream routers can support the functionality. For example, by using
an extended access list, you can allow DHCP traffic (instead of the unsupported DHCP relay feature) or
multicast traffic such as that created by IP/TV. You can also establish routing protocol adjacencies
through a transparent firewall; you can allow OSPF, RIP, EIGRP, or BGP traffic through based on an
extended access list. Likewise, protocols like HSRP or VRRP can pass through the ASA.
BPDU Handling
To prevent loops using the Spanning Tree Protocol, BPDUs are passed by default. To block BPDUs, you
need to configure an EtherType access list to deny them. If you are using failover, you might want to
block BPDUs to prevent the switch port from going into a blocking state when the topology changes.
See the
ARPs are allowed through the transparent firewall in both directions without an access list. ARP
traffic can be controlled by ARP inspection.
For Layer 3 traffic travelling from a low to a high security interface, an extended access list is
required on the low security interface. See
for more information.
TRUE broadcast destination MAC address equal to FFFF.FFFF.FFFF
IPv4 multicast MAC addresses from 0100.5E00.0000 to 0100.5EFE.FFFF
IPv6 multicast MAC addresses from 3333.0000.0000 to 3333.FFFF.FFFF
BPDU multicast address equal to 0100.0CCC.CCCD
AppleTalk multicast MAC addresses from 0900.0700.0000 to 0900.07FF.FFFF
"Transparent Firewall Mode Requirements" section on page 9-14
Information About the Firewall Mode
Chapter 19, "Adding an Extended Access Control List,"
Cisco ASA Series CLI Configuration Guide
for more information.
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