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layer3 switch has its own route table containing all routes used by that switch. Each route
entry in the route table specifies the VLAN interface should be used for forwarding packet
to reach a destination host or the next hop layer3 switch to the host.
The route table mainly consists of the following:
z Destination address: used to identify the destination address or destination
network of a packet.
z Network mask: used together with destination address to identify the destination
host or the segment the layer3 switch resides. Network mask consists of several
consecutive binary 1's, and usually in the format of dotted decimal (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 the
layer3 switch resides. For example, the network address of a host or the
segment the layer3 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: specify the interface of layer3 switch to forward IP packets.
z IP address of the next layer3 switch (next hop): specify the next layer3 switch the
IP packet will pass.
z Route entry priority: There may be several different next hop routes leading to
the same destination. Those 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; layer3
switch will choose one route for IP packet forwarding according to the priority
order.
To avoid too large 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 ES4626/ES4650 and the
default route lookup priority value.
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
15.2 Static Route
15.2.1 Introduction to Static Route
As mentioned earlier, the static route is the manually specified path to a network or a host.
Static route is simply and consistent, and can prevent illegal route modification, and is