H3C Technologies H3C SR8800 - Manual (Page 22)

6
Configuring static routing
Introduction
Static route
Static routes are manually configured. If a network’s topology is simple, you only need to configure static
routes for the network to work properly. The proper configuration and usage of static routes can improve
network performance and ensure bandwidth for important network applications.
The disadvantage of using static routes is that they cannot adapt to network topology changes. If a fault
or a topological change occurs in the network, the routes will be unreachable and the network breaks.
The network administrator has to modify the static routes manually.
Default route
Without a default route, a packet that does not match any routing entries is discarded.
A default route is used to forward packets that match no entry in the routing table. It can be configured
in either of the following ways:
• The network administrator can configure a default route with both destination and mask being
0.0.0.0. The router forwards any packet whose destination address fails to match any entry in the
routing table to the next hop of the default static route.
• Some dynamic routing protocols, such as OSPF, RIP and IS-IS, can also generate a default route. For
example, an upstream router running OSPF can generate a default route and advertise it to other
routers, which install the default route with the next hop being the upstream router.
Static route configuration items
Before you configure a static route, you must know the following concepts:
• Destination address and mask
In the ip route-static command, an IPv4 address is in dotted decimal format and a mask can be
either in dotted decimal format or in the form of mask length—the number of consecutive 1s in the
mask.
• Output interface and next hop address
When configuring a static route, specify either the output interface, next hop address, or both
depending on the specific occasion. The next hop address cannot be a local interface IP address;
otherwise, the route configuration will not take effect.
In fact, each route lookup operation has to find the next hop to resolve the destination link layer
address.
When you specify the output interface, follow these guidelines:
{
If the output interface is a Null 0 interface, no next hop address is required.
{
If the output interface is a point-to-point interface, no next hop address is required. You need
not change the configuration even if the peer’s address changes. For example, a PPP interface