Cisco ASA 5505 Configuration Manual page 360

Information About IPv6 Support
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For example, a packet destined for 192.168.32.1 arrives on an interface of an adaptive security appliance
with the following routes in the routing table:
hostname# show route
In this case, a packet destined to 192.168.32.1 is directed toward 10.1.1.2, because 192.168.32.1 falls
within the 192.168.32.0/24 network. It also falls within the other route in the routing table, but the
192.168.32.0/24 has the longest prefix within the routing table (24 bits verses 19 bits). Longer prefixes
are always preferred over shorter ones when forwarding a packet.
Dynamic Routing and Failover
Because static routing systems cannot react to network changes, they generally are considered unsuitable
for today's large, constantly changing networks. Most of the dominant routing algorithms today are
dynamic routing algorithms, which adjust to changing network circumstances by analyzing incoming
routing update messages. If the message indicates that a network change has occurred, the routing
software recalculates routes and sends out new routing update messages. These messages permeate the
network, stimulating routers to rerun their algorithms and change their routing tables accordingly.
Dynamic routing algorithms can be supplemented with static routes where appropriate. A router of last
resort (a router to which all unroutable packets are sent), for example, can be designated to act as a
repository for all unroutable packets, ensuring that all messages are at least handled in some way.
Dynamic routes are not replicated to the standby unit or failover group in a failover configuration.
Therefore, immediately after a failover occurs, some packets received by the adaptive security appliance
may be dropped because of a lack of routing information or routed to a default static route while the
routing table is repopulated by the configured dynamic routing protocols.
For more information about static routes and how to configure them, see the
Default Routes" section on page
Information About IPv6 Support
Many, but not all, features on the adaptive security appliance supports IPv6 traffic. This section describes
the commands and features that support IPv6, and includes the following topics:
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Cisco ASA 5500 Series Configuration Guide using ASDM
18-8
If the destination matches more than one entry in the routing table, and the entries all have the same
network prefix length, the packets for that destination are distributed among the interfaces
associated with that route.
If the destination matches more than one entry in the routing table, and the entries have different
network prefix lengths, then the packet is forwarded out of the interface associated with the route
that has the longer network prefix length.
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R 192.168.32.0/24 [120/4] via 10.1.1.2
O 192.168.32.0/19 [110/229840] via 10.1.1.3
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Features that Support IPv6, page 18-9
IPv6-Enabled Commands, page 18-9
Entering IPv6 Addresses in Commands, page 18-10
19-1.
Chapter 18 Information About Routing
"Configuring Static and
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