Length Of Subnet Masks; Name Resolving - Lantronix SCS Reference Manual

IP
To display the subnet mask, use the Show IP command.
Local>> SHOW IPSCS Version B1.1/102int(951128)
Hardware Addr: 00-80-a3-0b-00-5b
IP Address: 192.0.1.221
The SCS will not change the subnet mask once it is set. If the SCS IP address is changed to a different class,
for example, from a class B to a class C address, the subnet mask will remain a class B address.
The SCS supports CIDR (classless routing). CIDR allows Internet Service Providers (ISPs) to group blocks
of class C networks into larger networks. Your ISP will provide you with the appropriate subnet mask. If
you enter a CIDR subnet mask with the Set/Define IP Subnet command, the SCS will display a reminder
that classless routing is being used.
Local>> DEFINE IP ADDRESS 192.0.1.1
Local>> DEFINE IP SUBNET 255.255.240.0
%Info: Supernet (CIDR) mask set.

6.2.1 Length of Subnet Masks

Variable length subnet masks divide networks into subnetworks of different sizes. For example, if network
128.1.0.0 used variable length subnet masks, the subnet 128.1.4.0 might have subnet mask 255.255.255.0,
and subnet 129.1.224.0 might have subnet mask 255.255.255.240.
For the SCS to function properly, all subnetworks within a particular network must use the same subnet
masks even if each network has a subnet mask of a different length.

6.3 Name Resolving

TCP/IP hosts generally have an alphanumeric host name, such as athena, as well as a numeric IP address,
such as 192.0.1.35. As a text host name may be easier to remember than an IP address, users may use this
name to refer to the host during a Telnet connection attempt.
Network hosts do not understand alphanumeric (text) host names. When a text name is used, the SCS must
translate it into its corresponding IP address. The translation process is called name resolution.
To resolve a name, the SCS can use one of two resources: its local name table or the Domain Name Service
(DNS). For example, suppose user Bob wishes to telnet to athena.com. The SCS first consults its local host
table; if the name doesn't exist, the SCS attempts to resolve the name using the DNS. If the name cannot be
resolved, Bob must enter the IP address in order to access the host.
Some host names and IP addresses are added to the local host table by rwho packets, periodically
broadcasted by UNIX hosts that support the rwho protocol. If addresses are not learned from rwho packets
and DNS is not available, hosts may be manually added to the table. See Adding Hosts to the Host Table on
page 6-7 for instructions.
To use the DNS, the SCS must know the IP address of the DNS server.
Figure 6-11: Show IP Output
Figure 6-12: Using Classless Routing
6-6
Name:
Uptime:
Subnet Mask:
Name Resolving
DOC_SERVER
1 Day 22:49
255.255.255.0