3Com CoreBuilder 3500, Implementation Manual

Page: 272 / 592

272 C
HAPTER
11: I
NTERNET
P
ROTOCOL
(IP)
Routing Table With a routing table, a router or host determines how to send a packet
toward its ultimate destination. The routing table contains an entry for
every learned and locally defined network. The size of the routing table
on your system is dynamic and can hold at least 25,600 entries; the actual
number depends upon what other protocols are being routed.
A router or host uses the routing table when the destination IP address of
the packet is not on a network or subnet to which it is directly connected.
The routing table provides the IP address of a router that can forward the
packet toward its destination.
The routing table consists of the following elements:
■
Destination IP address — The destination network, subnet, or host.
■
Subnet mask — The subnet mask for the destination network.
■
Metric — A measure of the distance to the destination. In the Routing
Information Protocol (RIP), the metric is the number of hops through
routers.
■
Gateway — The IP address of the router interface through which the
packet travels on its next hop.
■
Status — Information that the routing protocol has about the route,
such as how the route was put into the routing table.
■
Time-to-live (TTL) — Time-to-live measured in seconds before this
learned route will time out.
Figure 48 shows the routing table contents of the router in Figure 47.
Figure 48 Sample Routing Table
Routing table
default route
158.101.1.0
158.101.2.0
158.101.3.0
Destination Subnet mask
255.255.255.0
255.255.255.0
255.255.255.0
255.255.255.0
Metric
2
2
2
2
Gateway
160.1.1.254
160.1.1.254
160.1.1.254
160.1.1.254
Status
learned - RIP
learned - OSPF - INTRA
learned - OSPF - INTRA
learned - OSPF - INTRA
TTL
170
---
---
---