Networks/Network Security (Ch. 3,4) Flashcards
OSI Model
_ open systems interconnection model layers (mnemonic: “all people seem to need data processing” – know layer numbers too)
_ (1) physical - hardware
_ (2) data link - switches that format data into data frames and route between systems on a local network using MAC addresses
_ (3) network - introduces IP addresses, routing between systems not on the same local network
_ (4) transport - end-to-end communication (e.g. TCP, UDP)
_ (5) session - establishes and manages sessions between apps
_ (6) presentation - translates data into standard format, provides encryption, compression, other data transformation
_ (7) application - provides network services to apps
TCP
_ transmission control protocol
_ 3-way handshake (client sends SYN, server sends SYN/ACK, client sends ACK)
UDP
_ user datagram protocol
_ connectionless (no 3-way handshake)
_ DoS attacks often use UDP
IP
_ internet protocol
_ IPv4 - 32 bits, dot-delimited numbers
_ IPv6 - 128 bits, colon-delimited hex
ICMP
_ internet control message protocol
_ tests basic connectivity
_ includes tools like ping and traceroute
_ DoS often uses ICMP
_ firewalls and routers often block to prevent DoS
TFTP
_ trivial file transfer protocol
_ transfers small amounts by FTP
_ used for comms with some devices
_ usually disabled to prevent attacks
TLS
_ transport layer security
_ replaced SSL
IPsec
_ internet protocol security
_ encrypts IP payload traffic
_ includes authentication header
SSH and SFTP port
22
HTTPS/TLS port
443
IMAP ports
_ internet message access protocol
_ 143 plaintext
_ 993 TCP
SMTP ports
_ simple main transfer protocol
_ 25 plaintext
_ 587 TLS (SMTPS)
POP3 ports
_ post office protocol
_ 110 plaintext
_ 995 TCP
Email gateway
_ network device or software app that filters external mail for an internal mail system
AD DS
_ Microsoft Active Directory Domain Services
_ uses TLS-encrypted LDAP
_ uses Kerberos for authentication
RTP/SRTP
_ real-time transport protocol
_ for audio and video over IP
_ includes VoIP
_ SRTP secures transmission
SIP
_ session initiation protocol
_ inits and manages voice/video sessions
_ establishes RTP/SRTP connection in cleartext
RDP
_ remote desktop protocol
OpenSSH
_ suite of tools that simplify use of SSH
_ supports SCP and SFTP
Create SSH key pair
_ ssh-keygen -t rsa
_ creates “id_rsa.pub”, the public key
_ creates “id_rsa”, the private key
_ use “ssh-copy-id” to copy public key to remove server
Private IPv4 addresses
_ any of form 10.x.y.z
_ 172.16.y.z - 172.31.y.z
_ 192.168.y.z
_ routers block all traffic from or to private IP addresses
Unique local IPv6 addresses
_ start with prefix FC00
DNS port
_ 53, for both TCP and UDP
DNS zone record types
_ A - host record for IPv4
_ AAAA - host record for IPv6
_ PTR - pointer record, used to provide reverse lookup from IP to domain name
_ MX - mail exchange record identifying a mail server
_ CNAME - canonical name record (aka alias record), assigns additional domains to an IP
_ SOA - start of authority record, providing domain or zon info such as TTL
TTL
_ time to live
_ duration of a DNS cache entry in seconds
DNS poisoning
_ replacing a DNS cache entry to an IP, causing domains to incorrectly resolve to the false IP
_ happens on the DNS server (DNS pharming is the client attack)
DNSSEC
_ domain name system security extensions
_ adds a digital signature to each DNS cache entry, providing integrity and authentication to DNS replies
_ helps prevent DNS poisoning
Unicast
_ 1-to-1 traffic between IP addresses (intervening hosts may see the data, but they won’t process it)
_ can’t be captured by a protocol analyzer
broadcast
_ 1-to-all traffic, sending traffic to all other hosts on a subnet using a broadcast address
_ 255.255.255.255 is an example broadcast address
_ every host processes broadcast traffic
_ switches pass broadcast traffic but not routers
switch
_ devices connect to a switch’s physical ports
_ internally connects ports
_ when it receives a packet from a port, it knows the MAC address of the device at that port
_ to send a packet to a MAC address for which it doesn’t have a port mapping, it sends packet to all ports
_ can limit MAC addresses per port for security
hub
_ broadcasts received data to all ports
_ switches provide better security
Switching loop
_ where output of one switch port enters another port of the switch
_ when looped data is broadcast, called a “broadcast storm”
_ can degrade performance
_ Spanning Tree Protocol (STP) can prevent this
_ Rapid STP can also prevent this
_ without prevention, easy to slow network to a crawl by connection two ports, such as within a conference room
BPDU
_ bridge protocol data unit
_ sent by STP (spanning tree protocol) to detect loops
_ edge ports should not be able to send this; if they do, problem discovered
router
_ routes traffic between network segments
_ don’t pass broadcasts between networks
_ each segment also called a “broadcast domain”
_ can implement ACL rules based on IP and port
Implicit deny
_ principle of ACLs by which all traffic that isn’t explicitly allowed is implicitly denied
_ the last rule of an ACL, if not the default behavior
_ routers and firewalls include the implicit deny rule
Default gateway
_ IP address of the router on the network
_ typically provides a path to the Internet
route command
_ shows known paths to other networks
_ shows the default gateway
SNMP
_ simple network management protocol
_ monitors and manages network devices such as routers and switches
_ can monitor device config
_ can have devices report status
_ can install agents on devices
_ only use SNMPv3, as it encrypts credentials
_ SNPMPv3 uses ports 161 and 162
Host-based firewall
_ monitors traffic to and from a single host (server or workstation)
_ many OSs provide a software-based firewall
Network-based firewall
_ usually a network appliance
_ has 2 or more NICs
Stateless firewall
_ applies ACL rules to traffic
_ a router is a stateless firewall
_ rules may specify protocol, source, destination, and port, in addition to the associated permission. Source and destination can include wildcards
Stateful firewall
_ bases decisions on traffic context or state
_ tracks sessions (e.g. after TCP handshake)
_ blocks traffic not part of a session
_ operate on transport layer (layer 4)
WAF
_ web application firewall
_ placed between web server and clients
_ can protect against XSS and other attacks
_ provides HTTP security on top of network security provided by a network firewall
_ analyzes all layers of firewall, so called a “layer 7 firewall”
First generation firewall
_ packet-filtering firewall
_ stateless
_ based decisions per packet
Second generation firewall
_ stateful
_ evaluates based on session state
NGFW
_ next-generation firewall
_ understand traffic for various apps
_ provides app-level inspection
_ performs content filtering and URL filtering
_ analyzes all layers of firewall, so called a “layer 7 firewall”
Failure modes
_ fail-open system - everything passes through when system fails, so no traffic disruption, but also no security
_ fail-closed system - nothing passes through when system fails, traffic disruption but provides security
Security zones
_ portion of network with its own security characterization
Screened subnet
_ aka demilitarized zone (DMZ)
_ security zone between private network and the Internet
_ by a firewall on both external and internal sides
_ contains servers that are to be available to the Internet, such as mail server, web server, and CA server
NAT
_ network address translation
_ translates public IP addresses to private IP addresses and back to public addresses
_ hosted by a NAT gateway
_ prevents public IPs from having to be purchased for each client
_ hides internal computers from the Internet
_ not compatible with IPsec
Static NAT
_ maps a private IP to a single public IP
Dynamic NAT
_ maps multiple public IPs, choosing based on load