Network technologies and trends » IOS commands

“No IP Routing” was the answer

Yasir Irfan — Mon, 20 Sep 2010 06:03:10 +0000

Recently one of our vendor added couple of new Cisco Catalyst 4506 Series distribution switches to our network for their PACS project. Those two newly added Cisco 4506 Series distribution switches are connected to our Core Cisco Catalyst 6513Series Switches using a layer 23 uplink ( as a trunk port). For VLAN redundancy we are using HSRP protocol. The newly added Cisco 4506 Series distribution switches are configured in VTP Client mode, we could see the VTP status was updated and all the VLAN were created. But there was a problem; there was not communication between any of the VLANS in the new Cisco 4506 Series distribution switches, after trouble shooting we figured out “ip routing” was enabled. When we disabled the ip routing with “no ip routing” command everything started working.

Remote Telnet useful tips!

Yasir Irfan — Tue, 08 Sep 2009 09:45:07 +0000

We all work remotely with Cisco routers and Switches, we often do login to do some configuration changes in the Cisco routers and Switches. What if we configured wrongly in the live Cisco routers and Switches which are located in the remote sites, we don’t enjoy the liberty of resetting the devices unless we have control over the power distribution.

In this scenario the “reload” command proves to be very handy and useful. Just before making any changes to the configuration we can use the “reload” command as demonstrated below

ITKE-Cisco#reload in ?

Delay before reload (mmm or hhh:mm)

ITKE-Cisco#reload in 10

System configuration has been modified. Save? [yes/no]: no

Building configuration…

[OK]

Reload scheduled in 10 minutes by yasir on vty0 (10.0.0.5)

Proceed with reload? [confirm]

ITKE-Cisco#

***

*** — SHUTDOWN in 0:05:00 —

***

The above demonstrated command will reload the device in 10 minutes. After applying the “reload” command we can proceed with the configuration changes. If things go wrong and we lost connectivity

to the device, then try back after 10 minutes as the device will get reloaded with the original startup-configuration which can helps us to restore the connectivity to the device.

Once we are sure about the new configuration and its working properly without any hassles there is always a way “reload cancel” command is there to cancel the reload.

ITKE-Cisco#reload cancel

I find this command to be very handy and useful especially when we have to telnet or SSH to remote Cisco router or a Switch.

How to configure DHCP Snooping in a Cisco Catalyst Switches.

Yasir Irfan — Sat, 22 Nov 2008 12:56:06 +0000

So here we go, with the configuration of DHCP snooping on a Cisco Switch. This feature protects the network by allowing the Cisco Switches to accept DHCP response message only from the authorized servers connected to the trusted interfaces in a Cisco Switch.

All Switch to Switch connections are configured as 802.1 1Q Trunk ports.

IP Address and HSRP Details for the Core Switches From the above scenario we have two Cisco 6513 Series Switches as a Core/ Distribution with three VLANS one for management of Switches VLAN 50,VLAN 100 for all the servers and VLAN 101 for clients. Two Cisco 3560 Series Switches as Server Farm Switches and a Cisco 3560 Series Switch as an Access Switch.There are two DHCP servers with an IP address 10.0.1.100 and 10.0.1.101 connected with Server Farm Switches with HP NIC teaming. We configure DHCP Snooping based on above scenario.

The first step to configure DHCP Snooping is to turn on DHCP snooping in all Cisco Switches using the “ip dhcp snooping” command.

All Cisco Switches (config)#ip dhcp snooping Second step is to configure the trusted interfaces, from the above scenario all trunk ports are configured as trusted ports as well as the interfaces G0/7,(ITKESF01 50.0.0.6), G0/17,(ITKESF02 50.0.0.7), G0/9 ITKESF01 50.0.0.6) and G0/18 ITKESF02 50.0.0.7) connected to DHCP servers with IP 10.0.1.100 and 10.0.1.101. Lets configure all trunk ports in ITKEBB01

ITKEBB01(config)#interface range gigabitEthernet 3/21 – 23

ITKEBB01 (config-if)#ip dhcp snooping trust

Now let’s configure all trunk ports in ITKEBB02

ITKEBB02(config)#interface range gigabitEthernet 3/21 – 23 ITKEBB02 (config-if)#ip dhcp snooping trust

ITKEBB02 (config)#interface gigabitEthernet 3/16

ITKEBB02 (config-if)#ip dhcp snooping trust

Now let’s configure the trusted ports for the DHCP servers

ITKESF01(config)#interface gigabitEthernet 0/7

ITKESF01 (config-if)#ip dhcp snooping trust

ITKESF01(config)#interface gigabitEthernet 0/17 ITKESF01 (config-if)#ip dhcp snooping trust

ITKESF02(config)#interface gigabitEthernet 0/9

ITKESF02 (config-if)#ip dhcp snooping trust

ITKESF02(config)#interface gigabitEthernet 0/18 ITKESF02 (config-if)#ip dhcp snooping trust

Now let’s configure the trunk ports Access Switch ITKEAS01

ITKEAS01(config)#interface range gigabitEthernet 0/49 – 52

ITKEAS01 (config-if)#ip dhcp snooping trust

Finally we are going to configure VLANS for DHCP snooping DHCP snooping will used on all the VLANs (VLAN 100 & 101)except management VLAN 50 . Also we will limit the requests rate received in the Access Switch (ITKEAS01) ALL SWITCHES(config)# ip dhcp snooping VLAN 100,101

ITKEAS01(config)#interface range gigabitEthernet 0/1 – 48

ITKEAS01 (config-if)#ip dhcp snooping limit rate 20

Displaying the DHCP snooping

For further reference please do check this article from Cisco about DHCP snooping.

How to configure SNMPv3 in a Cisco Catalyst Switch – Series 1

Yasir Irfan — Sun, 12 Oct 2008 05:17:50 +0000

Configuring SNMP Version 3 in a Cisco Catalyst Switch is bit more complicated compared to SNMP v1 and v2. But after configuring SNMPv3 you can relax as the SNMPv3 provides more security by adding authentication (username and password) as well as encryption to the protocol.

What is SNMPv3 ?Simple Network Management Protocol version 3. The specification for this Full Standard protocol is published in RFCs 3410 and 3418. SNMPv3 provides a Full Standard administrative framework (authorization, access control, etc.) and a remote configuration/administration MIB. Also check the SNMPv3 documentation from Cisco Systems.

How to configure SNMPv3 in a Cisco Catalyst Switch ?

First we begin with configuration of SNMPv3 on the Cisco Catalyst Switch by creating a SNMP “view”. A “view” defines what information can be accessed by the SNMP user/group when they query the SNMPv3 enabled Cisco Catalyst Switch. In the below example we will create “view” called ITKEView. We will enable “system” , “internet” and “interfaces” SNMP OIDS on the Cisco Catalyst Switch.

ITKE(config)# snmp-server view ITKEView internet includedITKE(config)# snmp-server view ITKEView system includedITKE(config)# snmp-server view ITKEView interfaces included

To be continued in next series

Things to be considered before upgrading an IOS in a Cisco 6500 Series Switch with SUP720- Series 3

Yasir Irfan — Mon, 06 Oct 2008 07:34:08 +0000

In the second series I was talking about the Compact flash memory, now let’s proceed further, one more key thing you must consider before starting an IOS upgrade for a Cisco Catalyst 6513 Switch with Supervisor Engine SUP720 is the redundant power supply. Make sure the Cisco Catalyst 6513 Switch is installed with the redundant power supply and they are connected to two different power sources. Suppose one power source fails then the other source can take care of the Cisco Catalyst 6513 Switch while the IOS upgrade is going on.

Things to be considered before upgrading an IOS in a Cisco 6500 Series Switch with SUP720- Series 2

Yasir Irfan — Sat, 04 Oct 2008 12:21:34 +0000

In the first series I was talking about the TFTP severs, now let’s proceed further, one more key thing you must consider before starting an IOS upgrade for a Cisco Catalyst 6513 Switch with Supervisor Engine SUP720 is the Compact flash memory. The Supervisor Engine SUP720 comes with two slots for memory. Recommended part number

MEM-C6K-CPTFL256M

Cat6500 Sup720 Compact Flash Mem 256MB

The Compact flash memory is required in order to avoid any failure IOS file upload through TFTP server. As before uploading the file the current IOS file is deleted from the boot flash memory of the switch. Before starting the IOS upgrade in the Cisco Catalyst 6513 Switch with Supervisor Engine SUP720 issue a boot command to boot from the flash memory if the Cisco Catalyst 6513 Switch with Supervisor Engine SUP720 fails to boot from the boot flash memory by issuing following command.Note: the Compact flash memory is inserted in the slot 1 of the Supervisor Engine SUP720.

How to configure intervlan routing between Cisco Catalyst Switches and HP Procurve Switches Series 2

Yasir Irfan — Wed, 24 Sep 2008 08:27:05 +0000

In my previous post I did discussed about the how common terminologies are applied by both Cisco & HP, now it’s time proceed further , in this example we will create two VLANs and make intervlan communication between HP Procurve Switches and Cisco Catalyst Switches.

We will create 2 VLANS in both Switches, as shown in the below table

Now let’s see what configuration commands required to create a VLAN, and enable intervlan communication between HP Procurve Switches and Cisco Catalyst Switches.

How to configure intervlan routing between Cisco Catalyst Switches and HP Procurve Switches Series 1.

Yasir Irfan — Mon, 22 Sep 2008 06:53:07 +0000

In this series of article you are going to experience how to configure VLAN trunking between HP Procurve Switches and Cisco Catalyst Switches.

Before proceeding further lest understand the basic terminoly applied by both Cisco and HP for the following things

When it comes to VLANs in Cisco every one thinks of the term TRUKING.

HP applies trunking for ether channel where as in Cisco it applies for VLANs

Let’s compare how both vendors define Trunking

Source:HP

VLAN Terminologies applied by Both Cisco & HP

to be continued in next series

How to reset/delete the password & configuraton on a Cisco WS-C350-48-SMI

Yasir Irfan — Mon, 08 Sep 2008 08:12:59 +0000

This article describes the procedure for resetting / delete the password & current configuration on a Cisco Catalyst WS-C3550-48-SMI.Model: WS-C3550-48-SMI
Warning: This procedure will remove the switch configuration. Be sure to have a backup of you current switch configuration before proceeding.The Cisco WS-C3550-48-SMI Catalyst switch is similar to most Catalyst switches and the procedure for resetting the password is the same.

Step 1: Connect the console cable to the switch and start your terminal program (HyperTerminal/Secure CRT). Console port settings are 9600,8,N,1

Step 2: Hold the MODE button (on the front of the switch) while you power on the switch.

Step 3: Hold the MODE button for a few seconds until you the System light stop flashing.Step 4: At this point, the switch should be in ROMmon mode. Step 5: From ROMmon mode, type: flash_initStep 6: From ROMmon mode, type: delete flash:config.textStep 7: From ROMmon mode, type: boot

At this point the switch will boot as normal with a new configuration and no password.

The best way to record the serial number for Cisco Devices for Remote support.

Yasir Irfan — Sat, 06 Sep 2008 10:40:39 +0000

Imagine if you are accesing the remote router and need to figure out the serial number for a router or the Circuit IDs of the serial interface, then you may start looking your docmented data or call the remote technician to help you out in figuring these details. The best and easy way to get these details in matter of seconds is to put the serial number of each device in the Banner MOTD, and the circuit IDs in the serial interface descriptions.