Lesson 9 Flashcards
Best practic network design and architecture guides
Cisco’s SAFE Architecture
Places in the Network
Switch, vs hub, vs router
switch - mac addresses - connects computers within the same network
hub - dumb switch
router - IP address - connect computers/devices to eachtoerh and other networks
Application protocols
http - defines the format of message through which web browsersand web servers communicat….
FTP - Tranfering files
SMTP - email servers
RTP (real time transport portocool) - network protocol for delivering autio and video over ip networks
DNS - you know what dns does
Layer 2 forwarding and Layer 3 forwarding
The basic function of a network is to forward traffic from one node to another
Layer 2 - switches - mac addresses within a local networks
Layer 3 - mutiple subnets. ip addresses. routers
ARP
• Address Resolution Protocol (ARP) -Map IP addresses to MAC addresses so that packets can be forwarded
• Routing protocols
• Communicate routing table updates
• Network segment and broadcast domain
A network segment is one where all the hosts attached to the segment can use local
(layer 2) forwarding to communicate freely with one another
The hosts are said to be withing broadcast domain
• Implementing network segments
Assuming an Ethernet network, network segments can be established physically by
connecting all the hosts in one segment to one switch and all the hosts in another
segment to another switch. The two switches can be connected by a router and
the router can enforce network policies or access control lists (ACL) to restrict
communications between the two segments
• Layer 3 subnets
Because enterprise networks typically feature hundreds of switching appliances and
network ports (not to mention wireless access and remote access), segmentation is
more likely to be enforced using virtual LANs (VLANs). Any given switch port can be
assigned to any VLAN in the same topology, regardless of the physical location of
the switch. The segmentation enforced by VLANs at layer 2 can be mapped to logical
divisions enforced by IP subnets at layer 3.
Network Topology and Zone
segments, vlans, subnets
network segment seperated physically at layer two. VLANs seperated logically at layer 2 to simplify wiring. Layer 3 can map subnets to VLANs.
zones
Zones represent isolated segments for hosts
that have the same security requirement, Traffic between zones is subject to filtering by
a firewall
zone types
Intranet, Extranet, Internet
Intranet - private
Extranet - business parterns, suppliers, customers
Internet - allows annonymous access
DMZs
- Demilitarized zones (DMZs) isolate hosts that are Internet-facing
- Communications through the DMZ should not be allowed
- Ideally use proxies to rebuild packets for forwarding
Bastion Hosts
DMZs (because they are internet facing)
- Not fully trusted by internal network
- Run minimal services
- Do not store local network account credentials
MitM
Man in the middle
MitM or on-path attack is where
the threat actor gains a position between two hosts, and transparently captures,
monitors, and relays all communication between the hosts.
For example, a MitM host could present a
workstation with a spoofed website form, to try to capture the user credential.
How to seure against a MitM attack
mutual authentication, where both
hosts exchange secure credentials, but at layer 2 it is not always possible to put these
controls in place.
MAC address cloning spponing
MAC hardware interface address - easy to change for a different value
ARP
arp—display the local machine’s Address Resolution Protocol (ARP) cache.
The ARP cache shows the MAC address of the interface associated with each IP
address the local host has communicated with recently.
arp poisoning
Broadcasting unsolicited ARP
replies to poison the cache of local
hosts with spoofed MAC address
• Attacker usually tries to
masquerade as default gateway (router)
- Attacher can either monitor and sent to the router or..
- perform a DoS attack by not forwarding the packets
Mac flooding
• Overwhelm switch memory to
trigger unicast flooding (used to store the switches mac address table)
• Facilitates sniffing
Loop Prevention
Ethernett switch (or bridge) - loopoing around and around. Prevented by Spanning Tree Protocol (STP)
STP
Spanning Tree Protocol - prevents looping by setting up switches or bridges in a heirarchy
Broadcast Storm
Looping results in a storm from an exponential increase in traffic
Storm control - A storm control setting on a switch is a backup mechanism to
rate-limit broadcast traffic above a certain threshold.
BDPU Guard
• Configure switches to defeat attempts to
engineer a loop
• Portfast setting configured for access ports
• BPDU guard disables port if STP traffic is
detected
Methods to prevent looping and broadcast storms
- spanning tree protocol
- Stom control configuration
- BDPU Guard
Physical Port Security
•Secure switch hardware • Physically disconnect unused ports • Disable unused ports via management interface
• MAC address limiting and filtering
Configuring MAC filtering on a switch means defining which MAC addresses are
allowed to connect to a particular port.
• Limit number of MAC changes
DHCP
DHCP is the protocol that allows a server to assign IP address information to
a client when it connects to the network.
DHCP Snooping
DHCP snooping inspects this traffic arriving on
access ports to ensure that a host is not trying to spoof its MAC address.
Dynamic ARP Inspection
Can be configured along with DHCP Snooping
prevents a host attached to an untrusted port from flooding the segment
with gratuitous ARP replies.
Ways to protect Ports
- Physical port security
- MAC address limiting and filtering
- DHCP snooping
- Dynamic ARP inspection