Accton Technology ES4626 - Manual (Page 359)

359
Chapter 13 Routing Protocol
13.1 Routing Protocol Overview
To communicate with a remote host over the Internet, a host must choose a proper
route via a set of routers or Layer3 switches.
Both routers and layer3 switches calculate the route using CPU, the difference is that
layer3 switch adds the calculated route to the switch chip and forward by the chip at wire
speed, while the router always store the calculated route in the route table or route buffer,
and data forwarding is performed by the CPU. For this reason, although both routers and
switches can perform route selection, layer3 switches have great advantage over routers
in data forwarding. The following describes basic principle and methods used in layer3
switch route selection.
In route selection, the responsibility of each layer3 switch is to select a proper
midway route according to the destination of the package received; and send the
package to the next layer3 switch until the last layer3 switch in the route send the
package to the destination host. A route is the path selected by each layer3 switch to
pass the package to the next layer3 switch. Route can be grouped into direct route, static
route and dynamic route.
Direct route refer to the path directly connects to the layer3 switch, and can be
obtained with no calculation.
Static route is the manually specified path to a network or a host; static route cannot
be changed freely. The advantage of static route is simple and consistent, and it can limit
illegal route modification, and is convenient for load balance and route backup. However,
as this is set manually, it is not suitable for mid- or large-scale networks for the route in
such conditions are too huge and complex.
Dynamic route is the path to a network or a host calculated by the layer3 switch
according to the routing protocols enabled. If the next hop layer3 switch in the path is not
reachable, layer3 switch will automatically discard the path to that next hop layer3 switch
and choose the path through other layer3 switches.
There are two dynamic routing protocols: Interior Gateway Protocol (IGP) and
Exterior Gateway protocol (EGP). IGP is the protocol used to calculate the route to a
destination inside an autonomous system. IGP supported by ES4624-SFP/ES4626-SFP
switch include RIP and OSPF, RIP and OSRF can be configured according to the
requirement. ES4624-SFP/ES4626-SFP switch supports running several IGP dynamic
routing protocols at the same time. Or, other dynamic routing protocols and static route
can be introduced to a dynamic routing protocol, so that multiple routing protocols can be