Network technologies and trends

June 21, 2008  5:42 AM

What is SSH ? and how it can be configured in a Cisco Switch.

Yasir Irfan Yasir Irfan Profile: Yasir Irfan

Secure Shell (SSH) – TCP Port 22

SSH stands for “Secure Shell”. SSH commonly uses port 22 to connect your computer to another computer on the Internet. It is most often used by network administrators as a remote login / remote control way to manage their business servers. Examples would be: your email administrator needs to reboot the company email server from his home, or your network administrator needs to reset your office password while she is away at a conference.

If remote access to a switch is necessary, then consider using SSH instead of telnet. SSH provides encrypted connections remotely. However, only IOS versions that include encryption support SSH. Also, to include SSH capability the switch may need to have its IOS updated.

Before using SSH on the switch, the administrator must configure the switch with the following commands: hostname, ip domain-name, and crypto key generate rsa. The following example sets the hostname to Switch.

Switch(config)# hostname Switch
Refer to the previous subsection on DNS for an example using the ip domain-name command.
The crypto key generate rsa command depends on the hostname and ip domain-name commands. This crypto command generates a Rivest, Shamir, Adleman (RSA) key pair, which includes one public RSA key and one private RSA key.
The following example shows this crypto command, including the two parameters, the name for the keys
(e.g., switch.test.lab) and the size of the key modulus (e.g., 1024), that are prompted for.

Switch(config)# crypto key generate rsa
The name for the keys will be: switch.test.lab
Choose the size of the key modulus in the range of 360 to 2048 for your
General Purpose Keys. Choosing a key modulus greater than 512 may
take a few minutes.
How many bits in the modulus[512]? 1024
Generating RSA keys…. [OK].

To restrict SSH access to the switch, configure an extended access-list (e.g., 101) that allows only the administrators’ systems to make these connections and apply this access-list to the virtual terminal lines. Allow only SSH connections to these lines by using the transport input ssh command. Set the privilege level to 0, and set the exec-timeout period to 9 minutes and 0 seconds to disconnect idle connections to these lines. Finally, use the login local command to enable local account checking at login that will prompt for a username and a password.

The following commands show the example configuration for SSH on the virtual terminal lines.

Switch(config)# no access-list 101
Switch(config)# access-list 101 remark Permit SSH access from
administrators’ systems
Switch(config)# access-list 101 permit tcp host any eq 22 log
Switch(config)# access-list 101 permit tcp host any eq 22 log
Switch(config)# access-list 101 deny ip any any log
Switch(config)# line vty 0 4
Switch(config-line)# access-class 101 in
Switch(config-line)# transport input ssh
Switch(config-line)# privilege level 0
Switch(config-line)# exec-timeout 9 0
Switch(config-line)# login local

The login local command cannot be used with AAA. Instead, use the login authentication command. Refer to the AAA section of this guide for more details.

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June 19, 2008  1:52 PM

Sample Campus Network Documentation Policy

Yasir Irfan Yasir Irfan Profile: Yasir Irfan

Network Documentation Policy
1.0 Overview
This network documentation policy is an internal IT policy and defines the requirements for
network documentation. This policy defines the level of network documentation required such as
documentation of which switch ports connect to what rooms and computers. It defines who will
have access to read network documentation and who will have access to change it. It also defines
who will be notified when changes are made to the network.
2.0 Purpose
This policy is designed to provide for network stability by ensuring that network documentation
is complete and current. This policy should complement disaster management and recovery by
ensuring that documentation is available in the event that systems should need to be rebuilt. This
policy will help reduce troubleshooting time by ensuring that appropriate personnel are notified
when changes are made to the network.
3.0 Documentation
The network structure and configuration shall be documented and provide the following
1. IP addresses of all devices on the network with static IP addresses.
2. Server documentation on all servers as outlined in the “Server Documentation”
3. Network drawings showing:
a) The locations and IP addresses of all hubs, switches, routers, and firewalls on the
b) The various security zones on the network and devices that control access
between them.
c) The locations of every network drop and the associated switch and port on the
switch supplying that connection.
d) The interrelationship between all network devices showing lines running between
the network devices.
e) All subnets on the network and their relationships including the range of IP
addresses on all subnets and net mask information.
f) All wide area network (WAN) or metropolitan area network (MAN) information
including network devices connecting them and IP addresses of connecting
4. Configuration information on all network devices including:
a) Switches
b) Routers
c) Firewalls
5. Configuration shall include but not be limited to:
a) IP Address
b) Netmask
c) Default gateway
d) DNS server IP addresses for primary and secondary DNS servers.
e) Any relevant WINS server information.
6. Network connection information including:
a) Type of connection to the internet or other WAN/MAN including T1,T3, frame
b) Provider of internet/WAN/MAN connection and contact information for sales and
c) Configuration information including net mask, network ID, and gateway.
d) Physical location of where the cabling enters the building and circuit number.
4.0 Access
The IT networking and some enterprise security staff shall have full access to all network
documentation. The IT networking staff shall have the ability to read and modify network
documentation. Designated enterprise security staff shall have access to read and change network
documentation but those not designated with change access cannot change it. Help desk staff
shall have read access to network documentation.
5.0 Change Notification
The help desk staff, server administration staff, application developer staff, and IT management
shall be notified when network changes are made including.
a) Reboot of a network device including switches, routers, and firewalls.
b) Changes of rules or configuration of a network device including switches, routers, and
c) Upgrades to any software on any network device.
d) Additions of any software on any network device.
Notification shall be through email to designated groups of people.
6.0 Documentation Review
The network or IT manager shall ensure that network documentation is kept current by
performing a monthly review of documentation or designating a staff member to perform a
review. The remedy or help desk requests within the last month should be reviewed to help
determine whether any network changes were made. Also any current or completed projects
affecting network settings should be reviewed to determine whether there were any network
changes made to support the project.
7.0 Storage Locations
Network documentation shall be kept either in written form or electronic form in a minimum of
two places. It should be kept in two facilities at least two miles apart so that if one facility is
destroyed, information from the other facility may be used to help construct the IT infrastructure.
Information in both facilities should be updated monthly at the time of the documentation

June 18, 2008  1:28 PM

Introduction to Free ware Bandwidth Monitoring software’s – Series 1

Yasir Irfan Yasir Irfan Profile: Yasir Irfan

Cacti is one of the great free ware bandwidth monitoring software works with SNMP. It’s RRD based tool, which makes use of MySQL server as a database, and completely driven by PHP.

What is Cacti?
Cacti is a resource monitoring software which used RRDtool to store data & the data is used to create graphs. Cacti’s greatest strength is it provides complex graphs easily. Cacti come with fast poller to collect data from different resources simultaneously & do have many user management features. It’s very user-friendly that even a layman can accustomed to figure out how it works with less effort.

Why Cacti?
In a single sentence, “Cacti, because it’s easy”. Installing and using Cacti is a very simple task and does not require indepth knowledge in networking or resource management. You can install and configure it in simple steps, which makes it an ideal software for newbie network administrators. Never-the-less , its so powerful and scalable that you can use it even in large networks with hundreds of devices

Cacti can be installed on many platforms like unix, linux and windows. I am concentrating on Windows XP . In order install a Cacti download a full integrated package from following links thanks to Rony and Dave Hope for hosting .
It’s pretty easy to install, make sure IIS is enabled and just follow the steps until you reached the final step where you are suppose to do some modifications which are attached with this post. Cacti Post Installation Instructions

Once you are done with installation then log on to the cacti local web port by following
http://IP Address of the PC/cacti/index.php with default username admin & password cactipw.

For Adding Devices and graphs access this link

For further details do log in to cacti forums and cacti web site

June 17, 2008  7:02 AM

Configuring HSRP in Cisco 6500 Switch

Yasir Irfan Yasir Irfan Profile: Yasir Irfan

Configuring HSRP in a Cisco 6500 Switch


June 17, 2008  6:48 AM

Introduction to Cisco port security and the reasons to implement

Yasir Irfan Yasir Irfan Profile: Yasir Irfan

A growing challenge facing network administrators is determining how to control who can access the organization’s internal network—and who can’t. For example, can anyone walk into campus LAN , plug in a laptop, and access the network? You might argue that the wall jack has no connection to a switch, but couldn’t someone just pull the Ethernet cable from a working PC and connect to the network that way?

You might think this an unlikely scenario, but it does happen. For example a salesmen coming in to demo products, and they would just pull the Ethernet jack off a PC and connect it to their laptop, hoping to get Internet access.

I turned to switch port security to help solve the problem. Let’s look at how we can use Cisco’s Port Security feature to protect our organization.

Understand the basics
In its most basic form, the Port Security feature remembers the Ethernet MAC address connected to the switch port and allows only that MAC address to communicate on that port. If any other MAC address tries to communicate through the port, port security will disable the port. Most of the time, network administrators configure the switch to send a SNMP trap to their network monitoring solution that the port’s disabled for security reasons. When using port security, we can prevent devices from accessing the network, which increases security.

Benefits to port Securty
The key benefits of Port Security are:
•Network Availability – Reduce campus wide network outages caused by broadcast storms by blocking non standard hubs and switches.
•Network Reliability – Network port bandwidth can be guaranteed if limited to one MAC address. Bandwidth can’t be guaranteed if other network devices are sharing the network port.
•DHCP Availability – Reduce the risk of over subscription of DHCP IP Address per VLAN by limiting one MAC address per port.
•Network Security – Limiting one MAC address per switch port is an attack mitigation strategy. Stops CAM tables flooding attacks forcing the switch into repeater mode. Tools like macof can be used for this type of attack.
•Future Proofing – The implementation of port authentication at the edge of the network (802.1x) will also limit user to one MAC address per port.

Applying Cisco Security Features to Solve Common Problems

Sample Configuration for port security
Configuring the Port Security feature is relatively easy. In its simplest form, port security requires going to an already enabled switch port and entering the port-security Interface Mode command. Here’s an example:

Switch)# config t
Switch(config)# int fa0/18
Switch(config-if)# switchport port-security ?
aging Port-security aging commands
mac-address Secure mac address
maximum Max secure addresses
violation Security violation mode

Switch(config-if)# switchport port-security

By entering the most basic command to configure port security, we accepted the default settings of only allowing one MAC address, determining that MAC address from the first device that communicates on this switch port, and shutting down that switch port if another MAC address attempts to communicate via the port. But you don’t have to accept the defaults.

Know your options
As you can see in the example, there are a number of other port security commands that you can configure. Here are some of your options:
switchport port-security maximum {max # of MAC addresses allowed}: You can use this option to allow more than the default number of MAC addresses, which is one. For example, if you had a 12-port hub connected to this switch port, you would want to allow 12 MAC addresses—one for each device. The maximum number of secure MAC addresses per port is 132.
switchport port-security violation {shutdown | restrict | protect}: This command tells the switch what to do when the number of MAC addresses on the port has exceeded the maximum. The default is to shut down the port. However, you can also choose to alert the network administrator (i.e., restrict) or only allow traffic from the secure port and drop packets from other MAC addresses (i.e., protect).
switchport port-security mac-address {MAC address}: You can use this option to manually define the MAC address allowed for this port rather than letting the port dynamically determine the MAC address.

Of course, you can also configure port security on a range of ports. Here’s an example:
Switch)# config t
Switch(config)# int range fastEthernet 0/1 – 24
Switch(config-if)# switchport port-security
However, you need to be very careful with this option if you enter this command on an uplink port that goes to more than one device. As soon as the second device sends a packet, the entire port will shut down.

View the status of port security
Once you’ve configured port security and the Ethernet device on that port has sent traffic, the switch will record the MAC address and secure the port using that address. To find out the status of port security on the switch, you can use the show port-security address and show port-security interface commands. Below are examples for each command’s output:
Switch# show port-security address
Secure Mac Address Table
Vlan Mac Address Type Ports Remaining Age
—- ———– —- —– ————-
1 0004.00d5.285d SecureDynamic Fa0/18 –
Total Addresses in System (excluding one mac per port) : 0
Max Addresses limit in System (excluding one mac per port) : 1024

Switch# show port-security interface fa0/18
Port Security : Enabled
Port Status : Secure-up
Violation Mode : Shutdown
Aging Time : 0 mins
Aging Type : Absolute
SecureStatic Address Aging : Disabled
Maximum MAC Addresses : 1
Total MAC Addresses : 1
Configured MAC Addresses : 0
Sticky MAC Addresses : 0
Last Source Address : 0004.00d5.285d
Security Violation Count : 0



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