Cisco 7604 Configuration Guide - Page 114

Transparent Mode Overview Chapter 5 Configuring the Firewall Mode Management Interface In addition to each bridge group management IP address, you can add a separate management interface that is not part of any bridge group, and that allows only management traffic to the FWSM. This feature is especially useful in multiple context mode so you can manage each context from a single interface. Interfaces for through traffic cannot be shared between contexts; however, the management VLAN can be shared across multiple contexts. Allowing Layer 3 Traffic Even though transparent mode acts as a bridge, Layer 3 traffic, such as IP traffic, cannot pass through the FWSM unless you explicitly permit it with an extended access list. The only traffic allowed through the transparent firewall without an access list is ARP traffic. ARP traffic can be controlled by ARP inspection. See the "Adding an Extended Access List" section on page 13-6 for more information. Allowed MAC Addresses The following destination MAC addresses are allowed through the transparent firewall. Any MAC address not on this list is dropped. • 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 Passing Traffic Not Allowed in Routed Mode In routed mode, some types of traffic cannot pass through the FWSM even if you allow it in an access list. The transparent firewall, however, can pass most types of traffic through using either an extended access list (for IP traffic) or an EtherType access list (for non-IP traffic). Note The transparent mode FWSM does not pass CDP packets, or any packets that do not have a valid EtherType greater than or equal to 0x600. For example, you cannot pass IS-IS packets. An exception is made for BPDUs, which are supported. For example, you can 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 FWSM. See Table 13-2 on page 13-7 for more information about allowing special traffic. Non-IP traffic (for example AppleTalk, IPX, BPDUs, and MPLS) can be configured to go through using an EtherType access list. 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. Catalyst 6500 Series Switch and Cisco 7600 Series Router Firewall Services Module Configuration Guide using ASDM 5-8 OL-20748-01