379
E
ES4710BD 10 Slots L2/L3/L4 Chassis Switch
The route table mainly consists of the following:
z
Destination address: used to identify the destination address or the destination network of a
packet.
z
Network mask: used together with destination address to identify the destination host or the
segment that the layer 3 switch resides. Network mask consists of several consecutive
binary 1's, and usually in the decimal format (an address consists of 1 to 4 255’s) When
“AND” the destination address with network mask, we can get the network address for the
destination host or the segment that the layer 3 switch resides in. For example, the network
address of a host or the segment that the layer 3 switch resides with a destination address of
200.1.1.1 and mask 255.255.255.0 is 200.1.1.0.
z
Output interface: specifies the interface of the layer 3 switch to forward IP packets.
z
IP address of the next layer 3 switch (next hop): specifies the next layer 3 switch that IP
packet will pass.
z
Route entry priority: There may be several different next hop routes leading to the same
destination. These routes may be discovered by different dynamic routing protocols or static
routes manually configured. The entry has the highest priority (smallest value) and becomes
the current best route. The user can configure several routes of different priority to the same
destination; the layer 3 switch will choose one route for IP packet forwarding according to
the priority order.
To avoid too large of a route table, a default route can be set. Once route table lookup fails, the
default route will be chosen for forwarding packets.
The table below describes the routing protocols supported by ES4710BD and the default route
lookup priority values.
Routing Protocols or route type
Default priority value
Direct route
0
OSPF 110
Static route
1
RIP 120
OSPF ASE
150
IBGP 200
EBGP 20
Unknown route
255
18.2 Static Route
18.2.1 Introduction to Static Route
As mentioned earlier, the static route is the manually specified path to a network or a host. A Static
route is simple, consistent and can prevent illegal route modification. It is convenient for load
balance and route backup, but also has its own defects. Static route, as its name indicates, is static, it
won’t modify the route automatically on network failure, and manual configuration is required on
such occasions, therefore it is not suitable for mid to large-scale networks.
Static route is mainly used for the following two conditions: 1) in stable networks to reduce the load
of route selection and routing data streams. For example, static routes can be used in route to STUB
network. 2) For route backup, configure static route in the backup line, with a lower priority than the
main line.
Static route and dynamic route can coexist; A layer 3 switch will choose the route with the highest
