3Com 5500 SI - Switch - Stackable, Configuration Manual

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16
IP R
OUTING
P
ROTOCOL
O
PERATION
IP Routing Protocol
Overview
Routers select an appropriate path through a network for an IP packet according to
the destination address of the packet. Each router on the path receives the packet
and forwards it to the next router. The last router in the path submits the packet to
the destination host.
In a network, the router regards a path for sending a packet as a logical route unit,
and calls it a hop. For example, in Figure 52, a packet sent from Host A to Host C
goes through 3 networks and 2 routers and the packet is transmitted through two
hops (represented by the bold arrows) and route segments. Therefore, when a node is
connected to another node across a network, there is a hop between these two
nodes and these two nodes are considered adjacent in the Internet. Adjacent routers
are two routers connected to the same network. The number of route segments
between a router and hosts in the same network is zero. A router can be connected
to any physical link that constitutes a route segment for routing packets through the
network.
When the Switch 5500 runs a routing protocol, it can perform router functions. In
this guide, a router and its icon represent either a generic router or a Switch 5500
running routing protocols.
Figure 52 About hops
Networks can be different sizes, so the segment lengths between two different pairs
of routers can also be different.
If a router in a network is regarded as a node and a route segment in the Internet is
regarded as a link, message routing in the Internet works in a similar way as the
message routing in a conventional network. The shortest route may not always be the
optimal route. For example, routing through three LAN route segments may be much
faster than routing through two WAN route segments.
A
Route
segment
B
C
A
R
R
Route
segment
R
R
R
A