Context-Based Access Control

What is CBAC?

Cisco's Context-Based Access Control (CBAC) is a component of the IOS firewall feature set. Similar to reflexive ACLs, CBAC enables dynamic modification of access lists to allow certain incoming flows by first inspecting and recording flows initiated from the protected internal network. However, whereas reflexive ACLs act solely on L2-L4 protocol attributes, CBAC is able to inspect all the way to the application layer, taking into consideration characteristics of a flow on a per-protocol basis (or context).

From the conceptual illustration, we see that there are four logical points (marked in blue) at which the router can inspect traffic:

1. Inbound on the internal interface
2. Outbound on the external interface
3. Inbound on the external interface
4. Outbound on the internal interface

While we can deploy independent, static ACLs at one, some, or all of these points simultaneously, CBAC is configured and operates per interface, dynamically modifying ACL entries facing one direction based on the traffic it sees flowing in the opposite direction.

For example, let's assume we first want to allow by default all traffic traversing the router from the internal LAN (192.168.0.0/24) toward the Internet (for our purposes, 10.0.0.0/8). This is already the case, as the router will of course forward all routable traffic when no access restrictions have been applied. We also want to deny by default all traffic flowing from the Internet toward the LAN; to accomplish this we can use a simple ACL to deny all IP traffic. We'll apply it to the external interface in the inbound direction (versus the internal interface outbound) so that the router itself is protected from untrusted traffic as well.

R1(config)# ip access-list extended DENY_ALL
R1(config-ext-nacl)# deny ip any any
R1(config-ext-nacl)# exit
R1(config)# interface f0/0
R1(config-if)# ip access-group DENY_ALL in

References:

http://packetlife.net/blog/2009/mar/10/ios-context-based-access-control-cbac/

Cisco IOS Access Control List

What is an access control list?

In the Cisco IOS, an access control list is a record that identifies and manages traffic. After identifying that traffic, an administrator can specify various events that can happen to that traffic.

What's the most common type of ACL?

IP ACLs are the most popular type of access lists because IP is the most common type of traffic. There are two types of IP ACLs: standard and extended. Standard IP ACLs can only control traffic based on the SOURCE IP address. Extended IP ACLs are far more powerful; they can identify traffic based on source IP, source port, destination IP, and destination port.

What are the most common numbers for IP ACLs?

The most common numbers used for IP ACLs are 1 to 99 for standard lists and 100 to 199 for extended lists. However, many other ranges are also possible.

• Standard IP ACLs: 1 to 99 and 1300 to 1999
• Extended IP ACLs: 100 to 199 and 2000 to 2699

How can you filter traffic using ACLs?

You can use ACLs to filter traffic according to the "three P's"—per protocol, per interface, and per direction. You can only have one ACL per protocol (e.g., IP or IPX), one ACL per interface (e.g., FastEthernet0/0), and one ACL per direction (i.e., IN or OUT).

How can an ACL help protect
my network from viruses?

You can use an ACL as a packet sniffer to list packets that meet a certain requirement. For example, if there's a virus on your network that's sending out traffic over IRC port 194, you could create an extended ACL (such as number 101) to identify that traffic. You could then use thedebug ip packet 101 detail command on your Internet-facing router to list all of the source IP addresses that are sending packets on port 194.

References:

http://www.techrepublic.com/article/cisco-ios-access-lists-10-things-you-should-know/5731134

Common Threats to Router and Switch Physical & Mitigation

There are typically four types of common threats for router and switch.

Hardware threats

Hardware threats involve threats of physical damage to the router or switch hardware. Mission-critical Cisco network equipment should be located in wiring closets or in computer or telecommunications rooms that meet these minimum requirements:

• The room must be locked with only authorized personnel allowed access.
• The room should not be accessible via a dropped ceiling, raised floor, window, duct-work, or point of entry other than the secured access point.
• If possible, use electronic access control with all entry attempts logged by security systems and monitored by security personnel.
• If possible, security personnel should monitor activity via security cameras with automatic recording.
• Hardware threats involve physical damage to network components, such as servers, routers, and switches

Electrical threats

Electrical threats include irregular fluctuations in voltage, such as brownouts and voltage spikes, Electrical threats, such as voltage spikes, insufficient supply voltage (brownouts), unconditioned power (noise), and total power loss, can be limited by adhering to these guidelines:

• Install uninterruptible power supply (UPS) systems for mission-critical Cisco network devices.
• Install backup generator systems for mission-critical supplies.
• Plan for and initiate regular UPS or generator testing and maintenance procedures based on the manufacturer-suggested preventative maintenance schedule.
• Install redundant power supplies on critical devices.
• Monitor and alarm power-related parameters at the power supply and device levels.

Environmental threats

Environmental threats include very low or high temperatures, moisture, electrostatic, and magnetic Interference Environmental threats, such as temperature extremes (too hot or too cold) or humidity extremes (too wet or too dry), also require mitigation. Take these actions to limit environmental damage to Cisco network devices:

• Supply the room with dependable temperature and humidity control systems. Always verify the recommended environmental parameters of the Cisco network equipment with the supplied product documentation.
• Remove any sources of electrostatic and magnetic interference in the room.
• If possible, remotely monitor and alarm the environmental parameters of the room.

Maintenance threats

Maintenance threats include not having backup parts or components for critical network components; not labeling components and their cabling correctly Maintenance threats include poor handling of key electronic components, electrostatic discharge (ESD), lack of critical spares, poor cabling, poor labeling, and so on. Maintenance-related threats are a broad category that includes many items. Follow the general rules listed here to prevent maintenance-related threats:

• Clearly label all equipment cabling and secure the cabling to equipment racks to prevent accidental damage, disconnection, or incorrect termination.
• Use cable runs, raceways, or both to traverse rack-to-ceiling or rack-to-rack connections.
• Always follow ESD procedures when replacing or working with internal router and switch device components.
• Maintain a stock of critical spares for emergency use.
• Do not leave a console connected to and logged into any console port. Always log off administrative interfaces when leaving a station.
• Do not rely upon a locked room as the only necessary protection for a device. Always remember that no room is ever totally secure. After intruders are inside a secure room, nothing is left to stop them from connecting a terminal to the console port of a Cisco router or switch.

References:

http://computernetworkingnotes.com/network-security-access-lists-standards-and-extended/mitigating-common-threats.html

Perimeter Router, Internal Router and Firewall

There are basically few types of perimeter router standards whereby each of them suits differently depending on the size of the corporate network, each standard also provides different level of protection against network attacks. The very basic of perimeter router i'm going to talk about is the "Standalone perimeter router" which is suitable for small business network due to the minimal cost but provides only 1 layer of security.


The standalone perimeter router basically means having a router which is placed between the outside network (Global) and internal network (Local). The router does basic filtering of unwanted traffics and provides minimal protection for the internal network.


The diagram below shows the example of the Standalone Perimeter Router Topology.

Standalone Perimeter Router Topology

The next standard will be the Perimeter router with a standalone firewall. The perimeter router will again be placed between the outside network (Global) and internal network (Local).  On top of that, there will be a firewall placed just before the perimeter router within the internal network. The firewall provides greater protection and flexibility such as having packet filtering, stateful filtering, application layer filtering and NAT which is suitable for medium to large business network.

The diagram below shows the example of the Perimeter Router and Firewall Topology. 

Perimeter Router and Firewall Topology

The last standard will have at least 3 layer of protection, the perimeter router, a standalone firewall and an internal router. The internal router is to provide mitigation function of the network in case the trusted network inside had been compromise to prevent spreading of the attacks to the DMZ side. On top of that, the router also provides better routing options thus improving the performance of the network.

The diagram below shows the example of the Perimeter Router, Firewall and internal router Topology. 

Perimeter Router, Firewall and internal router Topology.

References:

OLIVE TEACHING MATERIALS

Secure Perimeter Routers & Disable Services & Logging

Ingress and Egress Filtering

The ingress filtering blocks the packets outside the network with a source address inside the network. This helps to prevent an outside attacker spoofing the address of an internal machine.


The egress filtering  blocks the packets from inside the network containing a source address that is not inside. This helps to prevent an attacker within the network from launching IP spoofing attacks against external machines.


The diagram below shows the topology of the Cisco IOS router's ingress/egress filtering in a typical corporate network.

Access List Directional Filtering

The Cisco IOS ACL is used to define traffic. Once that traffic is defined, some action can then be taken on that traffic.

Commonly, an ACL is associated with the filtering of IP packets (Network Layer 3 of the OSI Model) as they pass through a router. In other words, it is used to permit or deny traffic through a router. However, if you just define the ACL only and don’t apply it to an interface using the access-group command, nothing happens.

The diagram below shows the topology of the Cisco IOS router's ACL filtering in a typical corporate network.

IOS Firewall Router

Context-Based Access Control (stateful traffic inspection)

CBAC is a stateful firewall which keeps track the state of network connections such as TCP and UDP traffic travelling across it. It creates opening in the ACLs at the interfaces that inspect the traffic by adding a temporary ACL entry for a specific session.


The openings are created when the internal network starts a session with the outside network that would normally be denied. The traffic is only allowed back through the firewall if it is part of the same session and has the correct properties that CBAC is looking for.


Authentication proxy

The HTTP-based authentication proxy provides dynamic, per-user authentication and authorization via TACACS+ and RADIUS protocols.


The diagram below is an example of the HTTP-based authentication proxy.

Intrusion Detection

Acts as an in-line intrusion detection sensor.
When a packet or packets match a signature, it can perform any of the following configurable actions:

• Alarm—Send an alarm to a Cisco IDS Director or Syslog server.
• Drop—Drop the packet.
• Reset—Send TCP resets to terminate the session.

It can Identifies up to 100 common attacks depending on release.

Securing Cisco Routers by Disabling Unused Services

Disable bootp Server
Test(config)# no ip bootp server
Disable CDP
Test(config)#no cdp run
Disable ip classless
Test(config)#no ip classless
Disable DNS lookup
Test(config)#no ip domain-lookup
Disable finger service
Test(config)#no ip finger
Disable HTTP
Test(config)#no ip http server
Disable ip mask-reply
Test(config-if)#no ip mask-reply
Disable IP-Directed Broadcast
Test(config-if)#no ip directed-broadcast
Disable IP Source Routing
Test(config)#no ip source-route
Disable IP Unreachable
Test(config-if)#no ip unreachables
Disable Small Servers
Test(config)#no service tcp-small-servers
Test(config)#no service udp-small-servers

Router Management (logging)

Event logging provides you visibility into the operation of a Cisco IOS device and the network into which it is deployed. Cisco IOS software provides several flexible logging options that can help achieve the network management and visibility goals of an organization.

Log Severity Levels:

Types of Logging method:

Console
Buffered
Terminal Line
Syslog
SNMP


Log Message Format:

References:

http://en.wikipedia.org/wiki/IP_address_spoofing
http://www.techrepublic.com/blog/networking/what-you-need-to-know-about-cisco-ios-access-list-filtering/536
http://ciscoskills.net/2011/02/22/understanding-cbac
http://www.debianadmin.com/securing-cisco-routers-by-disabling-unused-services.html
OLIVE INKS teaching materials