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Configuring a 2950 switch

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IP helper-address

Routers do not pass broadcast traffic, by default. There are instances where you may want a broadcast packet to pass through the router. An example is when a client sends a DHCP request to obtain an IP address and the DHCP server is on the other side of your router on another network.

In this instance, you can use the “ip helper-address” command, which will turn the broadcast into a multicast.

RouterA#config
RouterA(config)#interface fast ethernet 0
RouterA(config-if)#ip helper-address 192.168.1.1

The “ip helper-address” command will automatically forward eight common UDP ports that use broadcasts (we discuss port numbers in Module 7):

  • Time (37)
  • TACACS (49)
  • DNS (53)
  • BOOTP server (67)
  • BOOTP client (68)
  • TFTP (69)
  • NetBIOS name service (137)
  • NetBIOS datagram service (138)

IP forward-protocol

The “ip forward-protocol” command allows you to specify a number of protocols and ports that the router will forward. The example below specifies an IP helper address and then which protocol should be forwarded.

RouterA#config
RouterA(config)#interface fast ethernet 0
RouterA(config-if)#ip helper-address 192.168.1.1
RouterA(config-if)#ip forward-protocol udp

Cisco switches

Cisco offer several varieties of switch to cater for every type of business from small offices to large corporations. Due to the fact that Cisco acquired some of their early models of switches from buying smaller companies, there are a few different varieties of switch available running different types of software.

The 1800, 1900, and 2820 models of switch came originally from a company called Grand Junction. They run a menu-driven interface configuration and a hybrid Cisco type of IOS, which features a command-line interface. The 1900, 1800, and 2820 switches are for use in smaller companies who need limited functionality. They feature mostly Ethernet and some fast Ethernet ports.

The 3000 series of switches originate from Kalpana and the 8500 and 2900XL from Cisco. The catalyst 5000 originated from a company called Crescendo.

With a couple of exceptions the two main types of switch configuration are Cisco IOS and CATOS. The CATOS-set-based command-line interface is more limited than IOS based and uses “set” commands to configure the switch. The set-based switches include the 2926, 4000, 5000, and 6000 series switches.

IN THE EXAM: Cisco is moving to IOS-based switching almost exclusively. The CCNA exam does not test you on CATOS.

We will now look at configuration guides for the 2950 switch that uses Cisco IOS.

Configuring a 2950 switch

Press RETURN to get started!
2950 INIT: Complete

Cisco Internetwork Operating System Software
IOS (tm) C2950 Software (C2950-I6Q4L2-M), Version 12.1(20)EA1a, RELEASE
SOFTWARE (fc1)
Copyright (c) 1986-2004 by cisco Systems, Inc.
Compiled Mon 19-Apr-04 20:58 by yenanh
Image text-base: 0x80010000, data-base: 0x805A8000
We can set the hostname of the switch:

Switch>enable
Switch#config t
Enter configuration commands, one per line. End with CNTL/Z.
Switch(config)#hostname 2950
2950(config)#exit
And look at the version of IOS running on it:
2950#show version
Cisco Internetwork Operating System Software
IOS (tm) C2950 Software (C2950-I6Q4L2-M), Version 12.1(20)EA1a, RELEASE
SOFTWARE (fc1)
Copyright (c) 1986-2004 by cisco Systems, Inc.
Compiled Mon 19-Apr-04 20:58 by yenanh
Image text-base: 0x80010000, data-base: 0x805A8000

ROM: Bootstrap program is C2950 boot loader

Switch uptime is 11 minutes
System returned to ROM by power-on
System image file is "flash:/c2950-i6q4l2-mz.121-20.EA1a.bin"

cisco WS-C2950G-12-EI (RC32300) processor (revision E0) with 20713K bytes
of memory.
Processor board ID FHK0652X0PY
Last reset from system-reset
Running Enhanced Image
12 FastEthernet/IEEE 802.3 interface(s)
2 Gigabit Ethernet/IEEE 802.3 interface(s)

32K bytes of flash-simulated non-volatile configuration memory.
Base ethernet MAC Address: 00:0C:BE:D4:3C:40
Motherboard assembly number: 34-7410-05
Power supply part number: 34-0475-02
Motherboard serial number: FUY00LWXZ
Power supply serial number: PHI0648897W
Model revision number: E0
Motherboard revision number: A0
Model number: WS-C2950G-12-EI
System serial number: FHK0652X0PY
Configuration register is 0xF

Switches can be managed remotely in the same way a router can be. An IP address and default gateway can be configured on the switch. Since the switchports are layer 2 ports, they cannot be assigned an IP address. For this purpose a switch virtual interface (SVI), is created on the switch. SVI is a layer 3 interface and every VLAN can have one. SVIs are named after the VLAN ID, such as “Interface VLAN1”. The SVIs can be assigned an IP address.

The default management VLAN is VLAN 1. You can, however, change this.

For a management interface to become active you must create the VLAN, add an interface to the VLAN, and configure an IP address on the relevant SVI interface and a default gateway for IP traffic.

2950#conf t
Enter configuration commands, one per line. End with CNTL/Z.
2950(config)#interface vlan 2
2950(config-subif)#ip address 172.16.100.1 255.255.0.0
2950(config-subif)#exit
2950(config)#ip default-gateway 172.16.1.1
2950(config)#^Z
2950#
00:22:51: %SYS-5-CONFIG_I: Configured from console by console
2950#conf t
Enter configuration commands, one per line. End with CNTL/Z.
2950(config)#interface fastethernet 0/1
2950(config-if)#switchport mode access
2950(config-if)#switchport access vlan 2
2950(config-if)#exit

Apart from this, the switch will also require line VTY configuration and enable secret/ password configuration similar to a router:

2950(config)#enable secret cisco123
2950(config)#line vty 0 4
2950(config-line)#password cisco
2950(config-line)#login

Now, go through the Module 3 labs in the labs section in Part II.




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