Transcript IC30304pt2

IC3 - Network Security
M.Sc. in Information Security
Royal Holloway, University of London
1
IC3 - Network Security
Lecture 2, Part 1
Network Components and Protocols
2
Objectives of Lecture
CINS/F1-01
• Understand the different components that are
likely to be found in a network.
• Study the major network protocols (focussing
on TCP/IP networks).
• Develop an awareness of the inherent security
risks of using these components and protocols.
• Study a few ‘classic’ attacks on networks: ARP
spoofing,TCP Denial of Service, network
sniffing.
3
Contents
In this lecture, we take a layer-by-layer look at
the most important network components and
protocols, and associated security issues:
2.1
2.2
2.3
2.4
2.5
Network Cabling and Hubs (Layer 1)
Switches and ARP (Layer 2)
Routers and IP (Layer 3)
TCP and ICMP (Layer 4)
Network sniffers (multiple layers)
4
2.1 Network Cabling and Hubs
• TCP/IP Layer 1 (physical) devices.
• Cabling connects other components together.
• Hubs provide a point where data on one cable
can be transferred to another cable.
• We study their basic operation and associated
security issues.
5
Network Cabling
• Different Cabling Types:
– Thick Ethernet – 10BASE-5
– Thin Ethernet – 10BASE-2
– Shielded & Unshielded Twisted Pair (STP, UTP) –
10BASE-T (Cat 3) 100BASE-T (Cat 5)
6
Cabling in OSI Protocol Stack
7 Application
6 Presentation
5 Session
4 Transport
3 Network
2 DataLink
1 Physical
Cabling
7
Cabling Security Issues
• Physical Environment
– Trunking
– Network Closets
– Risers
• Physical Environment - Issues
–
–
–
–
–
–
Single or multi-occupancy
Access Control to floor building
Network passes through public areas
Network infrastructure easily accessible
Network infrastructure shares facilities
Electromagnetic environment
8
Thin Ethernet
• Short overall cable runs.
• Vulnerability: information broadcast to all devices.
– Threat: Information Leakage, Illegitimate Use.
• Vulnerability: One cable fault disables network.
– Threat: Denial of Service.
• Easy to install & attach additional devices.
– Threat: Illegitimate Use.
• Rarely seen now.
Thin Ethernet
9
UTP and Hub
•
•
•
•
•
Cable between hub and device is single entity.
Only connectors are at the cable ends.
Additional devices can only be added at the hub.
Disconnection/cable break rarely affects other devices.
Easy to install.
UTP
hub
10/100BASE-T
10
Other Layer 1 options
• Fibre Optic
–
–
–
–
Cable between hub and device is a single entity,
Tapping or altering the cable is difficult,
Installation is more difficult,
Much higher speeds – Gigabit Ethernet.
• Wireless LAN
– Popular where building restrictions apply,
– Several disadvantages:
• Radio signals are subject to interference, interception, and
alteration.
• Difficult to restrict to building perimeter.
– Security must be built in from initial network design.
– IEEE 802.11b.
– Discussed further in Lecture 8.
11
Hubs
• Data is broadcast to everyone on the hub
– Vulnerability: information broadcast to all devices.
• Threat: Information Leakage, Illegitimate Use.
– Vulnerability: Anyone can plug into hub.
• Threat: Illegitimate Use.
• OSI Layer 1.
• Intelligent Hubs:
– Signal regeneration,
– Traffic monitoring,
– Can be configured remotely.
12
Hubs in OSI Protocol Stack
7 Application
6 Presentation
5 Session
4 Transport
3 Network
2 DataLink
1 Physical
Cabling, Hubs
13
2.2 Switches and Layer 2 Issues
• More on Ethernet and IP addressing.
• Switch operation.
• Security issues for layer 2/switches - ARP
spoofing and MAC flooding.
• Safeguards.
14
Ethernet Addressing
• Address of Network Interface Card.
• Unique 48 bit value.
– first 24 bits indicate vendor.
• For example, 00:E0:81:10:19:FC.
– 00:E0:81 indicates Tyan Corporation.
– 10:19:FC indicates 1,055,228th NIC.
• Media Access Control (MAC) address.
15
IP Addressing
• IP address is 32 bits long – hence 4 billion ‘raw’
addresses available.
• Usually expressed as 4 decimal numbers
separated by dots:
– 0.0.0.0 to 255.255.255.255
– Typical IP address: 134.219.200.162.
• Many large ranges already assigned:
– 13.x.x.x Xerox, 18.x.x.x MIT, 54.x.x.x Merck.
– Shortage of IP addresses solved using private IP
addresses and subnetting/supernetting.
• More on addressing later.
16
IP Address to Ethernet Address
• Address Resolution Protocol (ARP):
– Layer 3 protocol,
– Maps IP address to MAC address.
• ARP Query
– Who has 192.168.0.40? Tell 192.168.0.20.
• ARP Reply
– 192.168.0.40 is at 00:0e:81:10:19:FC.
• ARP caches for speed:
– Records previous ARP replies,
– Entries are aged and eventually discarded.
17
ARP Query & ARP Reply
Web Browser
IP 192.168.0.20
MAC 00:0e:81:10:17:D1
Web Server
IP 192.168.0.40
MAC 00:0e:81:10:19:FC
(2) ARP Reply
192.168.0.40 is at
00:0e:81:10:19:FC
(1) ARP Query
Who has
192.168.0.40?
hub
10/100BASE-T
18
Switches
• Switches only send data to the intended
receiver (an improvement on hubs).
• Builds an index of which device has which
MAC address.
Device
MAC address
1
00:0e:81:10:19:FC
2
00:0e:81:32:96:af
3
00:0e:81:31:2f:d7
4
00:0e:81:97:03:05
8
00:0e:81:10:17:d1
switch
10/100BASE-T
19
Switch Operation
• When a frame arrives at switch:
– Switch looks up destination MAC address in index.
– Sends the frame to the device in the index that owns
that MAC address.
• Switches are often intelligent:
– Traffic monitoring, remotely configurable.
• Switches operate at Layer 2.
20
Switches in OSI Protocol Stack
7 Application
6 Presentation
5 Session
4 Transport
3 Network
2 DataLink
Switches
1 Physical
Cabling,Hubs
21
ARP Vulnerability
• ARP spoofing:
– Masquerade threat realised by issuing
gratuitous ARPs.
– ARP replies have no proof of origin, so a
malicious device can claim any MAC
address.
– Enables all fundamental threats!
22
Before ARP spoofing
IP 192.168.0.20
MAC 00:0e:81:10:17:d1
IP address
MAC address
192.168.0.40 00:0e:81:10:19:FC
192.168.0.1
00:1f:42:12:04:72
IP 192.168.0.40
MAC 00:0e:81:10:19:FC
IP address
Attacker
IP 192.168.0.1
MAC 00:1f:42:12:04:72
switch
MAC address
192.168.0.20 00:0e:81:10:17:d1
192.168.0.1
00:1f:42:12:04:72
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After ARP spoofing
IP 192.168.0.20
MAC 00:0e:81:10:17:d1
IP address
MAC address
192.168.0.40 00:1f:42:12:04:72
192.168.0.1
00:1f:42:12:04:72
Attacker
IP 192.168.0.1
MAC 00:1f:42:12:04:72
IP 192.168.0.40
MAC 00:0e:81:10:19:FC
IP address
MAC address
192.168.0.20 00:1f:42:12:04:72
192.168.0.1
00:1f:42:12:04:72
switch
(1) Gratuitious ARP
192.168.0.40 is at
00:1f:42:12:04:72
(2) Gratuitious ARP
192.168.0.20 is at
00:1f:42:12:04:72
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Effect of ARP spoofing
IP 192.168.0.20
MAC 00:0e:81:10:17:d1
IP address
IP datagram
Dest: 192.168.0.40
MAC: 00:1f:42:12:04:72
MAC address
192.168.0.40 00:1f:42:12:04:72
192.168.0.1
00:1f:42:12:04:72
Attacker
IP 192.168.0.1
MAC 00:1f:42:12:04:72
IP 192.168.0.40
MAC 00:0e:81:10:19:FC
IP address
MAC address
192.168.0.20 00:1f:42:12:04:72
192.168.0.1
00:1f:42:12:04:72
switch
Attacker’s relay index
IP address
MAC address
192.168.0.40 00:0e:81:10:19:FC
192.168.0.20 00:0e:81:10:17:d1
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Effect of ARP spoofing
• Attacker keeps a relay index: a table containing the true
association between MAC addresses and IP
addresses.
• But the two devices at 192.168.0.20 and 192.18.0.40
update their ARP caches with false information.
• All traffic for 192.168.0.20 and 192.168.0.40 gets sent
to attacker by layer 2 protocol (Ethernet).
• Attacker can re-route this traffic to the correct devices
using his relay index and layer 2 protocol.
• So these devices (and the switch) are oblivious to the
attack.
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Switch Vulnerability
• MAC Flooding
–
–
–
–
Malicious device connected to switch.
Sends multiple gratuitous ARPs.
Each ARP claims a different MAC address.
When index fills, some switches revert to hub behaviour: all
data broadcast.
Device
MAC address
1
1
00:0e:81:10:19:FC
2
4
00:0e:81:32:96:af
3
4
00:0e:81:32:96:b0
4
4
00:0e:81:32:96:b1
…
…
4
00:0e:81:32:97:a4
9999
switch
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Safeguards
• Physically secure the switch.
– Prevents threat of illegitimate use.
• Switches should failsafe when flooded.
– New threat: Denial of Service.
• Arpwatch: monitors MAC to IP address
mappings.
• Switch port locking of MAC addresses:
– Prevents ARP spoofing,
– But reduces flexibility (adding new host requires
reconfiguration of switch).
28
2.3 Routers and Layer 3 Issues
• Routers support indirect delivery of IP
datagrams.
• Employing routing tables.
– Information about possible destinations and how
to reach them.
• Three possible actions for a datagram:
– Sent directly to destination host.
– Sent to next router on way to known destination.
– Sent to default router.
• Routers operate at Layer 3.
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Routers in OSI Protocol Stack
7 Application
6 Presentation
5 Session
4 Transport
3 Network
Routers
2 DataLink
Switches
1 Physical
Cabling,Hubs
30
More on IP Addressing
•
•
•
•
IP addresses logically split into two parts.
First part identifies network.
Second part identifies host on that network.
Example: the IP address 192.168.0.20:
– 192.168.0.x identifies network.
– y.y.y.20 identifies host on network.
– We have a network with up to 256 (in fact 254) hosts (.0 and
.255 are reserved).
– The network mask 255.255.255.0 identifies the size of the
network and the addresses of all hosts that are locally
reachable.
– This mask can be fetched from network’s default router using
ICMP Address Mask Request message.
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Routers
Internet
Router
IP address
192.168.0.20
Network mask
255.255.255.0
Default router
192.168.0.254
62.49.147.169
192.168.1.11
192.168.0.40
192.168.1.10
62.49.147.170
Router
192.168.0.254
switch
192.168.1.254
switch
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Routers
Internet
Router
IP datagram
Dest: 192.168.0.40
IP address
192.168.0.20
Network mask
255.255.255.0
Default router
192.168.0.254
62.49.147.169
192.168.1.10
62.49.147.170
Router
192.168.0.40
192.168.0.254
switch
192.168.1.254 192.168.1.11
switch
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Routers
Internet
Router
IP datagram
Dest: 192.168.1.11
IP address
192.168.0.20
Network mask
255.255.255.0
Default router
192.168.0.254
62.49.147.169
192.168.1.10
62.49.147.170
Router
192.168.0.40
192.168.0.254
switch
192.168.1.254 192.168.1.11
switch
34
Routers
Internet
Router
IP datagram
Dest: 134.219.200.69
IP address
192.168.0.20
Network mask
255.255.255.0
Default router
192.168.0.254
62.49.147.169
192.168.1.10
62.49.147.170
Router
192.168.0.40
192.168.0.254
switch
192.168.1.254 192.168.1.11
switch
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Protocol Layering and Routing (TCP/IP)
Host A
Host B
Application Layer
Application Layer
HTTP Message
Transport Layer
Transport Layer
TCP Packet
Router
Internet Layer
Internet Layer
IP Datagram
Network Interface
Ethernet
Frame
IP Datagram
Network Interface
Physical Network
Internet Layer
Ethernet
Frame
Network Interface
Physical Network
36
Private Addressing
• Set of addresses have been reserved for use on
private networks (IETF RFC 1918):
– 10.0.0.0 to 10.255.255.255 (1 network, 224 hosts),
– 172.16.0.0 to 172.31.255.255 (16 networks, 216 hosts each),
– 192.168.0.0 to 192.168.255.255 (256 networks, 28 hosts
each).
• Packets with src/dest addresses in these ranges will
never be routed outside private network.
– Helps to solve problem of shortage of IP addresses.
– Security?
• Previous example: router has external IP address
62.49.147.170 and two internal addresses:
192.168.0.254 and 192.168.1.254:
– It acts as default router for two small private networks.
37
Some Layer 3 Security Issues – 1
• IP spoofing: IP addresses are not
authenticated, so dangerous to base security
on raw IP addresses alone.
– An attacker can place any IP address in the source
address of an IP datagram.
– An attacker can replay IP datagrams.
– Masquerade and integrity violation threats.
• Users have few guarantees about route taken
by their data.
– Information leakage threat.
38
Some Layer 3 Security Issues – 2
• Security of routing updates.
– Attacker may be able to corrupt routing tables on
routers by sending false updates.
– Denial of Service threat.
• What security is applied to protect remote
administration of routers?
– Attacker may be able to reconfigure or take control
of remote router and change its behaviour.
– Eg advertise attractive routes to other routers and so
bring interesting traffic its way.
39
2.4 TCP, ICMP and Layer 4 issues
• Each TCP connection begins with three
packets:
– A SYN packet from sender to receiver.
• “Can we talk?”
– An SYN/ACK packet from receiver to sender.
• “Fine – ready to start?”
– An ACK packet from sender to receiver.
• “OK, start”
• The packet type is indicated by a flag in the
packet header.
40
TCP Handshaking
TCP Packet
SYN flag
192.168.0.20
IP datagram
Src: 192.168.0.20
Dest: 192.168.0.40
192.168.0.40
TCP Packet
SYN & ACK flag
IP datagram
Src: 192.168.0.40
Dest: 192.168.0.20
TCP Packet
ACK flag
IP datagram
Src: 192.168.0.20
Dest: 192.168.0.40
41
Tracking TCP handshakes
• The destination host has to track which
machines it has sent a “SYN+ACK” to
• Keeps a list of TCP SYN packets that have had
a SYN+ACK returned.
• When ACK is received, packet removed from
list as connection is open.
42
TCP Denial Of Service
• What if the sender doesn’t answer with an
ACK?
– A SYN packet from sender to receiver.
• “Can we talk?”
– An SYN/ACK packet from receiver to sender.
• “Fine – ready to start?”
– ………………..nothing…………..……
• If the sender sends 100 SYN packets per
second
– Eventually receiver runs out of memory to track
the SYN+ACK replies.
– SYN flooding.
43
TCP Denial Of Service + IP Spoofing
• A host can place any IP address in the source
address of an IP datagram.
• Disadvantage: Any reply packet will return to
the wrong place.
• Advantage (to an attacker): No-one knows who
sent the packet.
• If the attacker sends 100 SYN packets per
second with spoofed source addresses….
44
TCP Denial of Service
192.168.0.20
TCP Packet
TCP Packet
SYN
TCPflag
Packet
SYN
flag
TCP
SYN Packet
flag
SYN flag
IP datagram
datagram
Src:IPIP
62.49.10.1
datagram
Src:
62.49.10.1
IP
datagram
Dest:Src:
192.168.0.40
62.49.10.1
Dest:Src:
192.168.0.40
62.49.10.1
Dest: 192.168.0.40
Dest: 192.168.0.40
192.168.0.40
TCP Packet
Packet
SYNTCP
&
ACK
flag
TCP
Packet
SYN &
ACK
flag
Packet
SYNTCP
& ACK
flag
SYN & ACK flag
IP datagram
datagram
Src: IP
192.168.0.40
IP
datagram
Src:
192.168.0.40
IP
datagram
Dest:
62.49.10.1
Src:
192.168.0.40
Dest:
Src:62.49.10.1
192.168.0.40
Dest:
62.49.10.1
Dest: 62.49.10.1
… the destination host will soon be unable to accept new
connections from legitimate senders.
45
TCP/IP Ports
• Many processes on a single machine may be
waiting for network traffic.
• When a packet arrives, how does the transport
layer know which process it is for?
• The port allows the transport layer to deliver
the packet to the application layer.
• TCP packets have source and destination
ports.
– Source port is used by receiver as destination of
replies.
46
Port Assignments
• Well known ports from 0 to 1023
–
–
–
–
–
–
http=port 80
smtp=port 25
syslog=port 514
telnet=23
ssh=22
ftp=21 + more…
• Registered ports from 1024 to 49151
• Dynamic or private ports from 49152 to 65535
47
Port Multiplexing
Host A
putty
Port
2077
ie
Host B
net
scape
Port 2076 Port
2078
Message
Transport Layer
telnet
apache
Port 23
Port 80
Transport Layer
Packet
Internet Layer
Internet Layer
Datagram
Network Layer
Network Layer
Frame
Physical Network
48
Ports in Action
192.168.0.20
HTTP message
GET index.html
www.localserver.org
HTTP message
Contents of
index.html
TCP Packet
Src Port: 2076
Dest Port: 80
TCP Packet
Src Port: 80
Dest Port: 2076
IP datagram
Src: 192.168.0.20
Dest: 192.168.0.40
IP datagram
Src: 192.168.0.40
Dest: 192.168.0.20
192.168.0.40
TELNET message
TELNET message
TCP Packet
Src Port: 2077
Dest Port: 23
TCP Packet
Src Port: 23
Dest Port: 2077
IP datagram
Src: 192.168.0.20
Dest: 192.168.0.40
IP datagram
Src: 192.168.0.40
Dest: 192.168.0.20
switch
49
Broadcast Addressing
• Broadcast IP addresses:
– Any packet with destination IP address ending .255
in a network with network mask 255.255.255.0 gets
sent to all hosts on that network.
– Similarly for other sizes of networks.
– A handy feature for network management, fault
diagnosis and some applications.
– Security?
50
ICMP
• ICMP = Internet Control Message Protocol.
• Layer 4 protocol (like TCP) carried over IP, mandatory
part of IP implementations.
• Carries IP error and control messages.
• ICMP Echo Request: test route to a particular host.
• Live host should reply with ICMP Echo Reply packet.
ICMP Packet
Echo
IP datagram
Src: 192.168.0.20
Dest: 192.168.0.40
ICMP Packet
Echo Reply
192.168.0.20
IP datagram
Src: 192.168.0.40
Dest: 192.168.0.20
192.168.0.40
51
ICMP ‘SMURF’ Denial of Service
Attacker
192.168.0.20
Victim
192.168.1.30
ICMP Packet
Echo Request
192.168.0.1
IP datagram
Src: 192.168.1.30
Dest: 192.168.0.255
192.168.0.2
ICMP Packet
ICMPReply
Packet
Echo
ICMP
Packet
Echo Reply
Echo Reply
IP datagram
datagram
Src:IP
192.168.0.1
IP
datagram
Src:192.168.1.30
192.168.0.2
Dest:
Src:192.168.1.30
192.168.0.3
Dest:
Dest: 192.168.1.30
ICMP Packet
Echo Reply
IP datagram
Src: 192.168.0.254
Dest: 192.168.1.30
192.168.0.3
.
.
.
192.168.0.254
52
Safeguards
• TCP Denial of Service is hard to defend against.
• Even more virulent: Distributed Denial of Service
(DDoS).
– attacker launches from many hosts simultaneously.
• Aggressively age incomplete TCP connections?
• Use firewall/IDS to detect attack in progress.
• Use relationship with IP service provider to investigate
and shut down DoS traffic.
• SMURF: drop most external ICMP traffic at boundary
firewall.
– There are other good reasons to do this: ICMP can be used as
tool by hacker to investigate your network…
53
2.5 Network Sniffers
• Network Interface Cards (NICs) normally
operate in non-promiscuous mode.
– Only listen for frames with their MAC address.
• A sniffer changes a NIC into promiscuous
mode.
– Reads frames regardless of MAC address.
• Many different sniffers:
– tcpdump
– ethereal
– Snort
54
Ethereal
55
Sniffing Legitimately
• Do they have legitimate uses?
– Yes … when used in an authorised and controlled
manner.
– Network analyzers or protocol analyzers.
– With complex networks, they are used for fault
investigation and performance measurement.
– Useful when understanding how a COTS product
uses the network.
56
Detecting Sniffers
• Very difficult, but sometimes possible.
– Tough to check remotely whether a device is
sniffing. Approaches include:
• Sending large volumes of data, then sending ICMP ping
requests.
• Sending data to unused IP addresses and watching for
DNS requests for those IP addresses.
• Exploiting operating system quirks.
– AntiSniff, Security Software Technologies.
57
Sniffer Safeguards
• Preventing attacks or limiting their effects.
– Basically a matter of network and system design
security.
– Examples of safeguards are:
•
•
•
•
Use of non-promiscuous interfaces.
Encryption of network traffic.
One-time passwords e.g. SecurID, skey.
Lock MAC addresses to switch ports – not effective.
58
IC3 - Network Security
Lecture 2, Part 2
Network Types
59
Objectives of Lecture
CINS/F1-01
• Examine the major different types of networks,
in increasing order of size and complexity:
LANs, MANs, WANs, Internet.
• Understand additional security threats for each
network type.
• Look at some possible safeguards for each
network type.
60
Contents
2.6
2.7
2.8
2.9
2.10
LANs
Networks at the building level
MANs
WANs
The Internet
61
2.6 Local Area Networks
• Local Area Networks (LANs) used within limited
areas (e.g. buildings/campuses) as opposed to
WANs (Wide Area Networks).
• Workgroup LAN: ‘An identifiable grouping of
computer and networking resources which may
be treated as a single entity.’
• The basic building block of larger networks.
– Large networks typically consist of interconnected
workgroup LANs.
• Security of workgroup LAN an essential
component of the overall network security in an
organisation.
62
IEEE 802
• The IEEE 802 standards have come to
dominate LANs. They specify protocols for use
at layers 1 and 2.
• ISO/IEC 8802-n = IEEE 802.n
• IEEE 802.2 = Layer 2 (most of).
• IEEE 802.3, 802.4 and 802.5 are three options
for Layer 1 (and a bit of Layer 2).
• IEEE 802.3 = Ethernet.
63
LAN Threats
• We have already seen several threats pertinent
to LANs in Lecture 2.1:
– Deficiencies of Thin Ethernet and Hubs: broadcast
data.
– Layer 1 threats: who has access to cabling,
broadcast wireless signals?
– Layer 2 threats: ARP spoofing, MAC flooding of
switches.
– Layer 3: IP spoofing.
– Layer 4 threats: TCP flooding, ICMP SMURF.
– Who can insert a sniffing device? Are hubs/switches
in locked cabinets?
64
2.7 Networks at the building level
• New threats to:
– Backbone which connects multiple workgroup LANs,
– Interconnections between the LAN and the
backbone,
– Control of information flow within a larger network,
– Network Management itself.
65
Backbone
Human
Resources
Finance
Sales
Backbone:
typically
routed via
risers or
under
floors.
Development
66
Network Backbone Threats – 1
Overview of threats:
• Backbone carries all inter-LAN traffic.
• Confidentiality:
– All data could be eavesdropped.
• Integrity:
– Any errors could affect all the network traffic.
• Availability:
– Loss of backbone means that workgroups would be
unable to communicate with each other.
67
Network Backbone Threats – 2
• Overview of Threats
– Point of interconnection between workgroup and
backbone is a sensitive area
– From security viewpoint it:
• Provides a point of access to the backbone
• Provides a point of access to all the data associated with a
workgroup
• Damage at this point could affect both the workgroup and
the backbone
68
LAN Safeguards – 1
• Partitioning
– With a building network there will be different types
of information being processed.
– Some types of data will require extra protection, e.g.
•
•
•
•
Finance
Personnel / Human Resources
Internal Audit
Divisional heads
– Two situations where extra controls are needed
• Physically separated group or team
• Widely distributed group of staff
69
LAN Safeguards – 2
• Partitioning
– Network configured so
that:
• Group workstations
cabled to their own
switch.
• Switches programmed to
restrict data flow onto the
backbone.
Firewall
Switch
– Add a Firewall
• Control all traffic to and
from hosts behind firewall.
Switch
70
LAN Safeguards 3 – VLANs
• VLAN is a virtual LAN.
• Switch is configured to divide up devices into VLANs.
• Device on one VLAN can’t send to devices
on another VLAN – security through partitioning.
switch
71
VLANs & Routers
• How to get from one VLAN to another?
– Connect them with a router.
– Router can exercise control over data flow.
– Only one switch needed, in place of two.
router
switch
72
Secure?
192.168.1.1
C
Layer 3…
Network 192.168.1.0
192.168.0.1
A
D
192.168.1.2
Network 192.168.0.0
B
…two perfectly
separated LANs
192.168.0.2
73
Secure?
Layer 2…
B
C
A
D
switch
• At Layer 3, the switch is ‘invisible’.
• At Layer 2, the switch becomes ‘visible’; the two LANs are actually
physically connected.
• Lesson: Important to examine network from layer 2 perspective as
well as layer 3 when assessing security.
74
LAN Safeguards – 4
• Extra controls
– If workgroup users are not located in a single area,
different measures must be adopted.
– In most cases, addressing is used to control traffic
flow but does not prevent traffic being read in transit.
– Higher level of security can be provided by
encryption, but:
• Does encryption mechanism understand the network
protocol?
• What is the performance impact of encryption?
• How are encryption keys generated, distributed, and
stored?
• Will a workstation on the encrypted workgroup be able to
communicate with an unencrypted server?
75
2.8 MANs
• Metropolitan Area Network.
• New Environment
– A network which encompasses several closely
located buildings (sometimes also called a campus
network).
• Such expanded network environments bring
additional security concerns:
– Network exposed to outside world,
– Problems of scale.
76
MAN example
Building C
Building A
Building B
77
MAN Threats
• Exposure to outside world:
– Network has left the security of the building.
– Small scale may rule out encryption.
– New risks must be assessed:
• Private campus or network crossing public areas?
• Links to business partners? What are there security
policies? Who are their staff?
• Dial-up access for remote users?
– Investigate constraints on solution:
• e.g. buried or elevated links.
– May need non-physical links:
• e.g. laser, infra-red, microwave, wireless.
78
MAN Threats
• Problem of scale
– Information flow must be controlled, and faulty
network components (in one building) must not
affect other buildings, so:
• Filters / bridges / firewalls will be needed
– Network Information Centre (NIC) is required.
– Specialised network management tools become
essential (manual approach no longer feasible).
• Possibility for greater integration – cable management
systems, device location maps, server disk space
monitoring, printer status,…
– Normally a second level backbone is used.
79
2.9 WANs
• Wide Area Network
– National or international network.
80
WAN Threats
• Threats become more significant:
– Sensitive data (including passwords) much more
widely transmitted.
– Greater organisational distances.
– Control may be more distributed.
– Outsourcing of network infrastructure to 3rd parties,
sharing of infrastructure with other customers.
– More staff, hence greater chance of insider attacks.
– More changes, hence greater risk of change
management errors.
– Greater demand for external connections increases
threat of unauthorised access by outsiders.
81
WAN Partitioning – 1
• Partitioning of networks using physical
separation:
– Provides good separation (!) and conceptually simple
– Legacy approach - in the days when adequate logical
separation was not possible, still done in very secure networks
– Sharing data is difficult and uncontrolled
– Costly and inflexible
Secure
Network
Sensitive
Applications
Open
Network
Other
Classified,
Operational,
Alarms, . . .
Applications
82
WAN Partitioning – 2
• Partitioning of networks using logical
separation:
– Closed User Groups:
• Multiple virtual networks on one physical one,
• Based on network addresses,
• Managed by the Network Management Centre.
–
–
–
–
Permanent Virtual Circuits (PVCs).
VLANs.
Protocol separation (IP,SNA, IPX).
Data confidentiality through encryption.
83
Encryption in WANs
• Encryption options and issues:
– Choice of physical media
– (Data) Link-level security (layer 2)
– End-to-end security
• Can be provided at layers 3, 4: IPSec, SSL
– Covered in more detail in Lectures 5 and 6.
• Or at layer 7 (application): SSH, secure e-mail
– SSH covered in Lecture 6, secure e-mail in Lecture 9.
84
Choice of Media for WANs
• Impact of different media on confidentiality:
– Fibre:
• Minimal external radiation,
• Special equipment required for tapping (special-purpose
US Navy submarine!),
• Normally a tap causes disruption of service.
– Satellite, radio or microwave:
• Extensive external radiation,
• Special (but easily available) equipment needed for
tapping,
• Tapping does not disrupt services,
• Carrier MIGHT provide some encryption.
85
Link Encryption
• Link encryption:
–
–
–
–
Offers data confidentiality for individual links,
Protocol independent (operates at layer 1/2),
Throughput is not normally an issue,
Moderate cost (£700-£1000 per unit).
• But link encryption for larger networks:
– Is expensive,
– Is a management burden,
– Does not scale well to large distributed networks,
– Data may not be protected at intermediate sites, in
switches, etc.
86
Conditions of Connection (COC)
• Imposed on users of networks by service
suppliers; counterpart to Service Level
Agreement (SLA).
• A powerful tool for network services department
when they do not have direct authority.
• Details users’ responsibilities:
•
•
•
•
•
•
Responsible for security of their end systems
Comply with COC’s standards
Control access to end-systems and equipment
Protect user-ids, passwords etc.
Become security aware
Support tests, investigations etc.
87
2.10 The Internet
• Internet evolved out of a US Government
funded network (ARPANET).
• Essentially a large collection of internetworked
networks.
• Developed in parallel with OSI so some conflict
between standards.
• Has its own protocols at layers 3 and 4: TCP
(layer 4) and IP (layer 3).
• Has pushed OSI out (de facto beats de jure).
• Now 5 million+ web sites, 200 million+ users.
• IETF: Internet Engineering Task Force
88
The Internet
• Internet presence and connection a prerequisite for
most corporations.
• Web browsing, email, file sharing and transfer, ecommerce, b2b commerce, e-government….
• Increasingly used for business critical applications.
• Possible to replace expensive WAN link with Internet
virtual private network (VPN) link.
• Threats become critical
– Route taken by sensitive data not guaranteed
– Availability not guaranteed
• Denial of service attacks are real risk
– Any Internet host can probe any other host
– Plenty of malicious content (viruses, trojans, pornography)
89
Some Internet Safeguards
• Firewalls to filter IP traffic, Intrusion Detection
Systems to detect penetrations.
• De-Militarized Zones to isolate Internet-facing
machines from internal networks.
• Content filters to filter email & web traffic
content.
• VPNs to protect critical data routed over public
Internet.
• Non-technical safeguards: policy, conditions of
use for employees, sanctions.
90
IC3 - Network Security
Lecture 2, Part 3
Network Management Security
91
Objectives of Lecture
CINS/F1-01
• Understand the need for security of network
management.
• Introduce the basic operation of the Simple
Network Management Protocol (SNMP).
• Evaluate the security of the different versions of
SNMP.
92
Contents
2.11 Network Management
2.12 SNMP overview
2.13 SNMP security
93
2.11 Network Management
• Management of complex networks is a difficult
task.
• Without network management, faults will:
– Disrupt network operation,
– Require substantial effort to identify,
– Require a long time to repair.
• Network Management facilities combined with
intelligent devices allow:
– Faults to be handled / identified locally,
– Alert messages to be raised and gathered centrally,
– Appropriate actions to be taken.
94
Network Management Tools
• Specialised tools are available (including HP
OpenView, IBM Netview, Cabletron Spectrum,
Sun NetManager).
• Common characteristics:
– Graphical interfaces,
– Collection of network alert messages,
– Ability to ‘drill down’ to examine the network and
traffic on it.
95
Network Management Protocols
• Network management protocols enable on-line
management of computers & networks.
• They support:
–
–
–
–
configuration management,
accounting,
event logging,
help with problem diagnosis.
• They are application layer protocols used for
communications by network management
systems.
Management Security
• But network management itself needs to be
secured!
• Two aspects to network management security
(as defined in ISO 7498-2):
– management of security:
• support provided by network management protocols for
provision of security services.
– security of management:
• means for protecting network management
communications.
2.12 SNMP Overview
• The Simple Network Management Protocol
(SNMP) is part of the Internet network
management system.
– Version 1 (1990/91) is specified in RFCs 1155-1157,
and 1212/1213.
– Version 2 (1993), with some security features, is
specified in RFCs 1441-1448.
– Version 3 (1999), with more complete security
features in RFCs 2570-2576
• All RFCs available at www.ietf.org.
SNMP V1 Architecture
Central MIB
Manager
Agent
SNMP
SNMP
UDP
UDP
IP
IP
Network
Network
Agent MIB
Physical Network
99
Architectural Model
• Model based on
– a network management station (a host system
running SNMP, with management s/ware)
– many network elements (hosts, routers, gateways,
servers).
• Management agent at a network device
implements SNMP
– provides access to the Management Information
Base (MIB).
SNMP Management
Management Station
Network
Elements
101
Connectionless Protocol
• Because V1 uses UDP, SNMP is a
connectionless protocol
– No guarantee that the management traffic is
received at the other entity
– Advantages :
• reduced overhead
• protocol simplicity
– Drawbacks :
• connection-oriented operations must be built into upperlayer applications, if reliability and accountability are
needed
• V2 & V3 can use TCP.
102
SNMP Operations
• SNMP provides three simple operations :
– GET : Enables the management station to retrieve
object values from a managed station;
– SET : Enables the management station to set object
values in a managed station;
– TRAP : Enables a managed station to notify the
management station of significant events.
• SNMP allows multiple accesses with a single
operation.
103
SNMP Protocol Data Units
• Get Request : Used to obtain object values from an
agent.
• Get-Next Request : Similar to the Get Request, except
it permits the retrieving of the next object instance (in
lexicographical order) in the MIB tree.
• Set Request : Used to change object values at an
agent.
• Response : Responds to the Get Request, Get-Next
Request and Set Request PDUs.
• Trap : Enables an agent to report an event to the
management station (no response from the manager
entity).
104
SNMP Port Numbers
• The UDP port numbers used for SNMP are :
161 (Requests) and 162 (Traps).
• Manager behaviour :
– listens for agent traps on local port 162;
– sends requests to port 161 of remote agent.
• Agent behaviour :
– listens for manager requests on local port 161;
– sends traps to port 162 of remote manager.
105
SNMP Messages
192.168.0.20
SNMP message
GET-REQUEST
UDP datagram
Src Port: 3042
Dest Port: 161
IP datagram
Src: 192.168.0.20
Dest: 192.168.0.254
192.168.0.254
SNMP message
GET-REQUEST reply
UDP datagram
Src Port: 161
Dest Port: 3042
IP datagram
Src: 192.168.0.254
Dest: 192.168.0.20
192.168.1.254
192.168.2.254
192.168.254.254
106
SNMP Message Format
• All SNMPv1 PDUs are built in the same way :
Version
Community
SNMP PDU
• Community:
– Local concept, defined at each device.
– SNMP community = set of SNMP managers allowed
access to a particular device.
– Each community is defined using a unique (within
the device) name, the community name.
• Each manager must specify a community in all
get and set operations.
107
Trap Examples
• Cisco router traps
– authentication
• device is the addressee of an SNMP protocol message that is not
properly authenticated. (SNMPv1 - incorrect community string)
– linkup
• device recognizes that one of the communication links
represented in the agent's configuration has come up.
– linkdown
• device recognizes a failure in one of the communication links
represented in the agent's configuration.
– coldstart
• device is reinitializing itself so that the configuration may be
altered.
– warmstart
• device is reinitializing itself, but the configuration will not be
altered.
108
2.13 SNMP Security
• SNMPv1 provides only trivial security
mechanisms, based on:
– Authentication Mechanism
– Access mode Mechanism
109
Authentication Mechanism
• Authentication Service: assure the destination
that the SNMP message comes from the
source from which it claims to be.
• Based on community name, included in every
SNMP message from a management station to
a device.
• This name functions as a password : the
message is assumed to be authentic if the
sender knows the password.
• No encryption of the community name.
110
SNMPv1 Key Vulnerability
• If an attacker can view the community string
– They can masquerade as a member of the
community by including the community string in
SNMP messages.
– The attacker may be able to manage any agent that
shares that community string.
111
Access Mode Mechanism
• Based on community profiles.
• A community profile consists of the combination
of :
– a defined subset of MIB objects (MIB view),
– an access mode for those objects (READ-ONLY or
READ-WRITE).
• A community profile is associated to each
community defined by an agent.
112
Security Threats
• Two primary threats:
– data modification - to an SNMP message,
– masquerade - impersonator might send false SNMP
messages.
• Two secondary threats:
– message stream modification - reordering, replay
and/or delay of SNMP messages,
– eavesdropping - on SNMP messages.
Security Services
• Later versions of SNMP have identified security
services required to meet threats:
–
–
–
–
–
data origin authentication,
data integrity,
message sequence integrity,
data confidentiality,
message timeliness & limited replay protection.
SNMPv3 User-Based Security Model
• A User, identified by UserName holds:
– Secret keys
– Other security information such as cryptographic
algorithms to be used.
• SNMPv3 entities are identified by
snmpEngineID.
– Each managed device or management station has
an snmpEngineID
115
Authoritative SNMP Entities
• Whenever a message is sent, one entity is
authoritative.
– For get or set, receiver is authoritative.
– For trap, response or report, sender is authoritative.
• Authoritative entity has:
– Localised keys
– Timeliness indicators
116
Timeliness Indicators
• Prevent replay of messages.
• Each authoritative entity maintains a clock.
• A non-authoritative entity has to retrieve the
time from the authoritative entity, confirm the
received value, then maintain a synchronised
clock.
• Messages can arrive within 150 seconds of
their generated time.
117
Keys
• Keys generated from user password.
• User provides password to all entities.
• Each entity generates a key from the password
and generates two further keys using the
entity’s snmpEngineID.
– One for data integrity/authentication
– One for confidentiality
118
Data Integrity and Authenticity
• Generate a MAC (cryptographic “fingerprint”) of
any message to be protected.
• Use HMAC algorithm with keys derived from
localized user key K1.
• Send the “fingerprint” with the message.
• Recipient with same key can check fingerprint
and be assured of integrity and authenticity of
SNMP message.
119
Data Confidentiality
• DES in Cipher Block Chaining mode.
• Second localised key.
• Has to be used together with Data Integrity and
Authenticity.
120
Management of SNMP security
• Following data needs to be managed:
– secret (authentication and privacy) keys,
– clock synchronisation (for replay detection),
– SNMP party information.
• SNMP can be used to provide key
management and clock synchronisation.
• After manually setting up some SNMP parties,
rest can be managed using SNMP.