Best Practices for VLANs Design

Because VLANs are a common security target, designing VLANs with security in mind is being proactive. Here are some best practices to use before you create the first VLAN on a switch.

VLAN Design Guidelines (3.3.2.1) 

VLAN configuration

Cisco switches have a factory configuration in which default VLANs are preconfigured to support various media and protocol types. The default Ethernet VLAN is VLAN 1. It is a security best practice to configure all the ports on all switches to be associated with VLANs other than VLAN 1. This is usually done by configuring all unused ports to a black hole VLAN that is not used for anything on the network. All used ports are associated with VLANs distinct from VLAN 1 and distinct from the black hole VLAN. It is also a good practice to shut down unused switch ports to prevent unauthorized access.

A good security practice is to separate management and user data traffic. The management VLAN, which is VLAN 1 by default, should be changed to a separate, distinct VLAN. To communicate remotely with a Cisco switch for management purposes, the switch must have an IP address configured on the management VLAN. Users in other VLANs would not be able to establish remote access sessions to the switch unless they were routed into the management VLAN, providing an additional layer of security. Also, the switch should be configured to accept only encrypted SSH sessions for remote management.

All control traffic is sent on VLAN 1. Therefore, when the native VLAN is changed to something other than VLAN 1, all control traffic is tagged on IEEE 802.1Q VLAN trunks (tagged with VLAN ID 1). A recommended security practice is to change the native VLAN to a different VLAN than VLAN 1. The native VLAN should also be distinct from all user VLANs. Ensure that the native VLAN for an 802.1Q trunk is the same on both ends of the trunk link.

DTP offers four switch port modes: access, trunk, dynamic auto, and dynamic desirable. A general guideline is to disable auto-negotiation. As a port security best practice, do not use the dynamic auto or dynamic desirable switch port modes.

Finally, voice traffic has stringent QoS requirements. If user PCs and IP phones are on the same VLAN, each tries to use the available bandwidth without considering the other device. To avoid this conflict, it is good practice to use separate VLANs for IP telephony and data traffic.

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Important Idea of Cisco Router Startup

Cisco Router Startup Procedure

Cisco Router

1.         POST; hardware tests

2.        Load and run bootstrap code; subsequent events

3.        Find the IOS software;

4.        Load the IOS software

5.        Find the configuration; the default location is NVRAM or TFTP

6.       Load the configuration

7.       Run

In-Band management is the process of using your network for management of a device (Ex: local subnet). Out-of-band management would be a modem dialing into a router’s auxiliary interface. The AUX port must be configured using the console port before it will function. A router contains five virtual terminal lines (0-4 VTY lines) to accept incoming Telnet sessions for in-band management. A Telnet session can also come from any interface. Every Cisco router has a console port that can be directly connected to a PC or terminal so that you can type commands at the keyboard and receive output on a terminal screen through a communications program, such as HyperTerminal. To set up out-of-band management with the connection between your terminal and Cisco console port you need to do the following:

1.     Cable the device using a rollover cable. You may need an RJ-45 to DB-9 or an RJ-45 to DB-25 adapter for your PC or terminal.

2.   Configure terminal emulation with the following COM port settings: 9600bps, 8 data bits, no parity, 1 stop bit, and no flow control.

There are two configuration files for Cisco routers one that is active and volatile (RAM), and one that the router uses to get configuration parameters during startup (stored in NVRAM).

A multi-protocol router maintains a separate routing table for each router protocol.

If a router does not know how to forward a packet, it will drop the packet. If it does know how to forward a packet, it changes the destination physical address to that of the next hop and transmits the packet. As the packet moves along the internetwork, its physical address changes but its protocol address remain constant. Routers each make independent routing decisions based on the local routing table. This is a hop-by-hop process, one step at a time.

Syslog messages are event messages that occur when the user is at the command line.

Cisco routers have the ability to copy its configuration to and from a TFTP (Trivial File Transfer Protocol) server. This is normally used in a WAN for remote router configuration. Cisco IOS does not support FTP. TFTP is UDP-based.

Cisco routers need at least four passwords set for minimal security: an enable password (primary router password), a console password, an auxiliary line password, and a VTY password (incoming telnet sessions).

Every Cisco router has a 16-bit configuration register, which is stored in a special memory location in NVRAM which allows the following functions: Force bootstrap program, select boot source, enable or disable the console break function, set terminal baud rate, load OS from ROM, and enable booting from TFTP.

Cisco routers can set the boot sequence by the BOOT command (EX: BOOT SYSTEM FLASH, BOOT SYSTEM ROM) (not as many features as the full IOS in flash), BOOT SYSTEM TFTP xxx.xxx.xxx.xxx). There may be as many BOOT TFTP commands as you would like for redundancy. Be careful of the order used to boot the router!

“Router” is the default hostname for all Cisco routers; the character following the hostname tells you what mode you are in. The part of Cisco IOS that provides the user interface and interprets the commands you type is called the command executive, or EXEC.

MD5 (Message Direct 5) is a one-way cryptographic algorithm used for encoding data, particularly passwords.

Enabling IPX routing automatically enables IPX RIP, Enabling Appletalk routing automatically enables RTMP. IP Routing must be manually configured. more about Cisco to know.

                                            Thank you