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S2989G-24TX Operation Manual

Chapter 4 Routing Protocol Related Configuration

4-2

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 associated.

EGP is used to exchange routing information among different autonomous systems,

such as BGP protocol. EGP supported by switch include BGP-4, BGP-4+.

4.1.1

Routing 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 layer3 switch has its own route table containing all routes used by that switch. Each

route entry in the route table specifies the physical port 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:

 Destination address: used to identify the destination address or destination

network of an IP packet.

 Network mask: used together with destination address to identify the destination

host or the network 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 network 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.

 Output interface: specify the interface of layer3 switch to forward IP packets.

 IP address of the next layer3 switch (next hop): specify the next layer3 switch the

IP packet will pass.

 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 with the highest priority

(smallest value) 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 prevent too large route table, a default route can be set. Once route table look up

fails, the default route will be chosen for forwarding packets.

The table below describes the routing protocols supported by switch and the default

route look up priority value.

Routing Protocols or route type

Default priority value