H3C Technologies H3C SecPath F1000-E - Manual (Page 356)

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IP routing overview
NOTE:
•
The term "router" in this chapter refers to both routers and Layer 3 firewalls.
• 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 router.
Upon receiving a packet, a router determines the optimal route based on the destination address and
forwards the packet to the next router in the path. When the packet reaches the last router, it then
forwards the packet to the destination host.
Routing provides the path information that guides the forwarding of packets.
Routes can be divided into the following categories by destination:
• Network route—The destination is a network. The subnet mask is less than 32 bits.
• Host route—The destination is a host. The subnet mask is 32 bits.
Based on whether the destination is directly connected to the router, routes can be divided into the
following types:
• Direct routes—The destination is directly connected to the router.
• Indirect routes—The destination is not directly connected to the router.
A router selects optimal routes from the routing table, and sends them to the forwarding information base
(FIB) table to guide packet forwarding. Each router maintains a routing table and a FIB table.
Routes in a routing table can be divided into the following categories by origin:
• Direct routes—Routes discovered by data link protocols, also known as "interface routes."
• Static routes—Routes manually configured. Static routes are easy to configure and require less
system resources. They work well in small and stable networks. Static routes cannot adjust to
network changes. You must manually configure the routes again whenever the network topology
changes.
• Dynamic routes—Routes that are discovered dynamically by routing protocols.
A routing table includes the following key items:
• Destination address—Destination IP address or destination network.
• Network mask—Specifies, in company with the destination address, the address of the destination
network. A logical AND operation between the destination address and the network mask yields
the address of the destination network. For example, if the destination address is 129.102.8.10 and
the mask 255.255.0.0, the address of the destination network is 129.102.0.0.
• Outgoing interface—Specifies the interface through which a matching IP packet is to be forwarded.
• IP address of the next hop—Specifies the address of the next router on the path. If only the outgoing
interface is configured, its address will be the next hop.
• Priority for the route—Routes to the same destination but having different next hops may have
different priorities and be found by various routing protocols or manually configured. The optimal
route is the one with the highest priority (with the smallest metric).