1
IP routing basics
Hardware compatibility
The A5500 SI Switch Series does not support configuring Layer 3 Ethernet interfaces.
The A5500 SI Switch Series does not support VPN-related parameters.
The A5500 SI Switch Series does not support OSPF, BGP, IS-IS, OSPFv3, IPv6 BGP, or IPv6 IS-IS.
Overview
IP routing directs the forwarding of IP packets on routers based on a routing table. This book focuses on
unicast routing protocols. For more information about multicast routing protocols, see
IP Multicast
Configuration Guide
.
The term "router" in this chapter refers to both routers and Layer 3 switches.
The types of interfaces that appear in any figures other than the network diagrams for configuration
examples are for illustration only. Some of them might be unavailable on your switch.
The term "interface" in the routing features collectively refers to Layer 3 interfaces, including VLAN
interfaces and Layer 3 Ethernet interfaces. You can set an Ethernet port as a Layer 3 interface by using
the
port link-mode route
command (see
Layer 2—LAN Switching Configuration Guide
).
Routing table
A router maintains at least two routing tables: one global routing table and one forwarding information
base (FIB). The FIB table contains only the optimal routes, and the global routing table contains all routes.
The router uses the FIB table to forward packets. For more information about the FIB table, see
Layer 3—IP
Services Configuration Guide
.
Routes can be classified by different criteria, as shown in
Table 1
Categories of routes
Criterion Categories
Destination
•
Network route
—Destination is a network. The subnet mask is less than 32 bits.
•
Host route
—Destination is a host. The subnet mask is 32 bits.
Whether the
destination is directly
connected
•
Direct route
—Destination is directly connected.
•
Indirect route
—Destination is indirectly connected.
Origin
•
Direct route
—A direct route is discovered by the data link protocol on an interface,
and is also called an "interface route."
•
Static route
—
A static route is manually configured by an administrator.
•
Dynamic route
—
A dynamic route is dynamically discovered by a routing protocol.
