Cabletron Systems SSR-GLX19-02, User Manual

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Chapter 8: Configuring IP Interfaces for the SSR
108 CoreWatch User’s Manual
on network 11.0.0.0, has a network address of 11.0.0.2. The router has two interfaces and
connects to both networks. (You can say the router is “well connected.”)
To communicate with one another through the router, the hosts make entries in routing
tables as shown in the following table. For example, host A communicates with host B by
using the route specified with the 11.0.0.0 10.0.0.1 entry in the host A routing table. That
entry states that host A uses the router at 10.0.0.1 as a gateway when it wants to
communicate with host B on the 11.0.0.0 network.
The previous table provides information about network routes rather than host routes. If
the previous table was providing information about host routes rather than network
routes, each host’s routing table would list the other host’s IP address as the destination.
When a packet is sent, the entire route is not known at the source. Instead, packets travel
to their destination one hop at a time. At each stop, a router calculates the next destination
by matching the destination address with entries in that router's routing table. This is
similar to sending a letter through the United States postal service. The envelope has the
ultimate destination address. Each post office along the way checks the ultimate
destination and determines the next-hop (the next post office). When the letter gets to the
post office that is serving the address on the envelope, the letter is delivered directly to the
address.
In addition to providing connectionless deliveries, IP fragments and reassembles packets.
IP does not guarantee that the packets will arrive in order or at all, nor does IP report
packet errors back to the source. Guarantee delivery is the responsibility of TCP, and the
reporting of packet errors is the responsibility of ICMP.
A Look at IP Addresses
When configuring the SSR, you will be required to enter IP address information. These 32-
bit addresses, which identify a
connection to a network
rather than a particular system,
include both a network ID and a host ID. If a network is part of the internet, the network
Table 10. Network destination and gateway routes
Host A Router Host B
Destination Gateway Destination Gateway Destination Gateway
10.0.0.0 10.0.0.2 11.0.0.0 11.0.0.1 11.0.0.0 11.0.0.2
11.0.0.0 10.0.0.1 10.0.0.0 10.0.0.1 10.0.0.0 11.0.0.1
Host A Host B Router
10.0.0.0 11.0.0.0
10.0.0.2 11.0.0.1 10.0.0.1 11.0.0.2