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Chapter 15 Routing Protocol
Configuration
To communicate with a remote host over the Internet, a host must choose a proper route
via a set of routers/L3 switches.
Both routers or 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 a great advantage over
routers in data forwarding. ES4626/ES4650 is a layer3 switch.. The following describes
basic theory 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 packet received; and send the packet to the next
layer3 switch until the last layer3 switch in the route sends the packet to the destination
host. A route is the path selected by each layer3 switch to pass the packet to the next
layer3 switch. Routes 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 routes cannot be
changed freely. Static routes are simple, consistent, and can limit illegal route
modifications, and are convenient for load balancing 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 ES4626/ES4650 include routing
protocols like RIP and OSPF, RIP and OSRF can be configured according to the
requirement. ES4626/ES4650 supports running several IGP dynamic routing protocols at
the same time. Or, other dynamic routing protocols and static route can be introduced in a
dynamic routing protocol, so that multiple routing protocols can be associated.
15.1 Route Table
As mentioned before, layer3 switch is mainly used to establish the route from the current
layer3 switch to a network or a host, and to forward packets according to the route. Each