Specifications

4-4
System Management Software Configuration Guide for Cisco IE 2000U and Connected Grid Switches
Chapter 4 Administering the Switch
Information About Administering the Switch
DNS
The DNS protocol controls the Domain Name System (DNS), which is a distributed database for
mapping hostnames to IP addresses. When you configure DNS on your switch, you can substitute the
hostname for the IP address with all IP commands, such as ping, telnet, connect, and related Telnet
support operations.
IP defines a hierarchical naming scheme that allows a device to be identified by its location or domain.
Domain names use period delimiters. For example, Cisco Systems is a commercial organization that IP
identifies by a com domain name, so its domain name is cisco.com. A specific device in this domain, for
example, the File Transfer Protocol (FTP) system is identified as ftp.cisco.com.
To track domain names, IP has defined the concept of a domain name server, which holds a cache (or
database) of names mapped to IP addresses. To map domain names to IP addresses, you must first
identify the hostnames, specify the name server that is present on your network, and enable the DNS.
MAC Address Table
The MAC address table contains address information that the switch uses to forward traffic between
ports. All MAC addresses in the address table are associated with one or more ports. The address table
includes these types of addresses:
• Dynamic address: a source MAC address that the switch learns and then ages when it is not in use.
• Static address: a manually entered unicast address that does not age and that is not lost when the
switch resets.
The address table lists the destination MAC address, the associated VLAN ID, and port number
associated with the address and the type (static or dynamic).
Building the Address Table
With multiple MAC addresses supported on all ports, you can connect any port on the switch to
individual workstations, repeaters, switches, routers, or other network devices. The switch provides
dynamic addressing by learning the source address of packets it receives on each port and adding the
address and its associated port number to the address table. As stations are added or removed from the
network, the switch updates the address table, adding new dynamic addresses and aging out those that
are not in use.
The aging interval is globally configured. However, the switch maintains an address table for each
VLAN, and STP can accelerate the aging interval on a per-VLAN basis.
The switch sends packets between any combination of ports, based on the destination address of the
received packet. Using the MAC address table, the switch forwards the packet only to the port associated
with the destination address. If the destination address is on the port that sent the packet, the packet is
filtered and not forwarded. The switch always uses the store-and-forward method: complete packets are
stored and checked for errors before transmission.
MAC Addresses and VLANs
All addresses are associated with a VLAN. An address can exist in more than one VLAN and have
different destinations in each. Unicast addresses, for example, could be forwarded to port 1 in VLAN 1
and ports 1, 9, and 10 in VLAN 5.