CHAPTER
1-1
Cisco ASA Series CLI Configuration Guide
1
Routing Overview
This chapter describes underlying concepts of how routing behaves within the ASA, and the routing
protocols that are supported.
This chapter includes the following sections:
• Information About Routing, page 1-1
• How Routing Behaves Within the ASA, page 1-4
• Supported Internet Protocols for Routing, page 1-5
• Information About the Routing Table, page 1-5
• Disabling Proxy ARPs, page 1-11
Information About Routing
Routing is the act of moving information across an internetwork from a source to a destination. Along
the way, at least one intermediate node typically is encountered. Routing involves two basic activities:
determining optimal routing paths and transporting information groups (typically called packets)
through an internetwork. In the context of the routing process, the latter of these is referred to as packet
switching. Although packet switching is relatively straightforward, path determination can be very
complex.
This section includes the following topics:
• Switching, page 1-1
• Path Determination, page 1-2
• Supported Route Types, page 1-2
Switching
Switching algorithms is relatively simple; it is the same for most routing protocols. In most cases, a host
determines that it must send a packet to another host. Having acquired a router address by some means,
the source host sends a packet addressed specifically to a router physical (Media Access Control
[MAC]-layer) address, this time with the protocol (network layer) address of the destination host.
As it examines the packet destination protocol address, the router determines that it either knows or does
not know how to forward the packet to the next hop. If the router does not know how to forward the
packet, it typically drops the packet. If the router knows how to forward the packet, however, it changes
the destination physical address to that of the next hop and transmits the packet.
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