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Alteon Application Switch Operating System Application Guide
Basic IP Routing
Document ID: RDWR-ALOS-V2900_AG1302
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Defining IP Address Ranges for the Local Route Cache
A local route cache lets you use Alteon resources more efficiently. The local network address and
local network mask parameters (accessed via the
/cfg/l3/frwd/local/add
command) define a
range of addresses that are cached on Alteon. The local network address is used to define the base
IP address in the range that will be cached. The local network mask is applied to produce the range.
To determine if a route should be added to the memory cache, the destination address is masked
(bit-wise AND) with the local network mask and checked against the local network address.
By default, the local network address and local network mask are both set to 0.0.0.0. This produces
a range that includes all Internet addresses for route caching: 0.0.0.0 through 255.255.255.255.
To limit the route cache to your local hosts, you could configure the parameters as shown in
Table 17:
Dynamic Host Configuration Protocol
The Dynamic Host Configuration Protocol (DHCP) is a transport protocol that provides a framework
for assigning IP addresses and configuration information to other IP hosts or clients in a large TCP/IP
network. Without DHCP, the IP address must be entered manually for each network device. DHCP
allows a network administrator to distribute IP addresses from a central point and send a new IP
address when a device is connected to a different place in the network.
DHCP is an extension of another network IP management protocol, the Bootstrap Protocol (BOOTP),
with an additional capability of dynamically allocating reusable network addresses and configuration
parameters for client operation.
Built on the client/server model, DHCP allows hosts or clients on an IP network to obtain their
configurations from a DHCP server, thereby reducing the network administration effort. The most
significant configuration the client receives from the server is its required IP address. Other optional
parameters include the "generic" file name to be booted, the address of the default gateway, and so
on.
The DHCP relay agent eliminates the need to have DHCP/BOOTP servers on every subnet. It allows
the administrator to reduce the number of DHCP servers deployed on the network and to centralize
them. Without the DHCP relay agent, there must be at least one DHCP server deployed at each
subnet that has hosts that need to perform the DHCP request.
DHCP Relay Agent
DHCP is described in RFC 2131, and the DHCP relay agent supported on Alteon is described in RFC
1542. DHCP uses UDP as its transport protocol. The client sends messages to the server on port 67
and the server sends messages to the client on port 68.
DHCP defines the methods through which clients can be assigned an IP address for a finite lease
period and allows reassignment of the IP address to another client later. Additionally, DHCP provides
the mechanism for a client to gather other IP configuration parameters it needs to operate in the
TCP/IP network.
In the DHCP environment, Alteon acts as a relay agent. The DHCP relay feature (
/cfg/l3/bootp
)
enables Alteon to forward a client request for an IP address to two BOOTP servers with configured IP
addresses.
Table 17: Example Local Routing Cache Address Ranges
Local Host Address Range Local Network Address Local Network Mask
0.0.0.0–127.255.255.255 0.0.0.0 128.0.0.0
128.0.0.0–128.255.255.255 128.0.0.0 128.0.0.0 or 255.0.0.0
205.32.0.0–205.32.255.255 205.32.0.0 255.255.0.0