Security Design.

Transcription

1 Security Design

2 Content Security Design Analysing Design Requirements Resource Separation a Security Zones VLANs Tuning Load Balancing

3 Analysing Design Requirements Answering the following questions What resources need to be protected? Who are potential attackers? What are the business needs? What are the policy constraints?

4 Gathering requirements What resources need to be protected? Servers Workstations Network equipment / VPN / dial-up

5 Gathering requirements Who are potential attackers? Outsider Insider Unsophisticated attacker Malicious software agents

6 Gathering requirements What are the business needs? Costs Cost-risk-mitigation Performance Delays (e.g. through encryption, logging) Bandwidth (e.g. VPN) Business-related services (e.g. web server) Fault tolerance Intra-system redundancy Intra-side redundancy Geographic redundancy

7 Gathering requirements What are the policy constraints? Analyzing documents describing policies Need to update policies?

8 Design elements Firewalls Perimeter Inline Routers Cabling VPN gateways Access control Group policies Policies External devices (ISP routers, external VPN)

9 Resource Separation Security Zones VLANs Security zones Remember what happens when VPN users are connected with internet as well Logical grouping of resources according to their security classification What are meaningful groups? To answer this question, two other questions have to be answered Who needs to access services? How much risk is involved in using certain services? Zones can spread across a single subnet or multiple subnets Zones within a server (e.g. chroot)

10 Resource Separation Security Zones VLANs DMZ Separating all accessible services into a zone Trust between DMZ and internal network is limited but higher than within external and internal network Firewalls and other appliances guard DMZ from external network and internal network from DMZ Attacker has to break both barriers Examples Web servers Mail relays Split DNS

11 Resource Separation Security Zones VLANs Wireless networks WLANs are easily accessible from off a company s premises Unsecured WEP Useful protection WPA VPN Wireless subnet is a good candidate for a separated network

12 Resource Separation Security Zones VLANs VLANs reduce costs when subnets spread across several locations Ethernet frames are tagged with a VLAN ID (see IEEE 8021Q) 802.1Q) Protection of VLAN tags against manipulation is hard to accomplish Frames might be send into private subnets (VLANs)

13 Tuning - Load balancing Performance and security are sometimes competing design goals. Security process are time consuming, remember Encryption / decryption Signing / signature checking Firewalling / proxying Security processes consume bandwidth Packet size when authentication of packets is used (signatures) Tunneling

14 Tuning - Load balancing Performance factors (What are users complaining i about?) Bandwidth Frequency Medium (copper vs. fiber cabling) Latency Propagation Gateway processing Response time Throughput Availability Parallel users MTBF

15 Tuning - Load balancing Network architecture Broadcast domains vs. gateway processing Security aspects of separation WAN links (decentralized / centralized) Routing principles Distance vector vs. link state Physical location

16 Tuning - Load balancing Load balancing Load that exceeds the capabilities of any single device is being distributed to a group of equal devices Round robin DNS Load balancing appliances (Layer 4 and layer 7 dispatchers) Problems Stateful protocols Sessions (e.g. hybrid encryption)

17 Summary Security design is a process of gathering the requirements, analyzing possibilities, and implementing security features. Security and performance are competing. Security has to deal with performance limitations imposed by itself.