Routing Through The Routing Table - H3C SecPath F1800-A Operation Manual

Operation Manual - Network and Routing Protocol
H3C SecPath F1800-A Firewall
through the shortest route is not always the most ideal way. For example, routing
through 3 LAN route segments may be much faster than that through 2 WAN route
segments.

2.1.2 Routing through the Routing Table

The key for a router to forward packets is the routing table. Each router saves a
routing table in its memory. Each entry of this table specifies the physical port of the
router, through which the packet to a subnet or a host should be sent. Therefore, it can
reach the next router in this path or reach the very destination host in the directly
connected network.
A routing table has the following key entries:
Destination address
It is used to identify the destination IP address or the destination network of an IP
packet. It is 32 bits in length.
Network mask
It is made up of several consecutive "1"s, which can be expressed either in the dotted
decimal format or by the number of the consecutive "1" s in the mask.
Combining with the destination address, it is used to identify the network address of
the destination host or router. With the destination address operates AND with the
network mask, you will get the address of the network segment where the destination
host or router is located.
For example, if the destination address is 129.102.8.10, the address of the network
where the host or the router with the mask 255.255.0.0 is located will be 129.102.0.0.
Output interface
It explains through which interface an IP packet should be forwarded.
Next hop address
It refers to the next router that an IP packet will pass through.
Priority added to the IP routing table for a route
There may be several next hops to the same destination. These routes may be
discovered by different routing protocols, or they can just be the static routes
configured manually. The one with the highest priority, that is, the smallest numerical
value, will be selected as the current optimal route.
Based on destinations, the routes can be divided into:
Subnet route
The destination is a subnet.
Host route
The destination is a host.
Chapter 2 IP Routing Protocol Overview
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