Server Network Communications Flashcards
OSI layer 7
- application
- may/may not involve user interaction
- OSs can use layer without user knowledge/consent
OSI layer 6
- presentation
- how data is presented
- differing character sets
- encryption/decryption
OSI layer 5
- session
- session establishment/maintenance/tear-down
- doesn’t imply authentication
- session IDs
OSI layer 4
- transport
- end-to-end data transmission
- can require acknowledgement of sent data
- port addresses/numbers
OSI layer 3
- network
- routing of network packets
- IP addresses
- routers
- layer 3 switches
OSI layer 2
- data link
- methods of accessing transmission media
- MAC addresses
- bridges
- NICs
- layer 2 switches
OSI layer 1
- physical
- electrical specifications
- cables
- connectors
- wireless specifications
- hubs
- repeaters
cable placement
- cable management arms
- cable management trays
- cable channels built into rack
- plastic cable ties
- hook and loop fasteners
- avoid thick bundles of cables/cable trays hampering fire suppression/airflow
cable labeling
- label network wall jacks
- label opposite end of cable on patch panel
- label patch cables
copper cables
- shielded twisted pair (STP)
- unshielded twisted pair (UTP)
- 8 wires/4 pairs
- each wire twisted at specific rate to reduce crosstalk
- higher transmission rate (frequencies)/greater number of twists per inch
- straight-through
- crossover
- rollover (connect locally to network equipment)
copper cable connectors
- RJ-11 (4 wire phone cables)
- RJ-45 (UTP/STP cables)
CAT5
- supports 100BASE-T IEEE ethernet standard
- 10/100 Mbps max transmission rate
- 100 MHz
CAT5e
- gigabit ethernet
- supports 1000BASE-T IEEE ethernet standard
- 1 Gbps (1000 Mbps) max transmission rate
- 100 MHz
CAT6
- more resistant to interference due to additional shielding
- supports 1000BASE-TX/10GBASE-T standards
- 1 Gbps (100m) max transmission rate
- 10 Gbps (55m) max transmission rate
- 250 MHz
CAT6A
- more extensive than CAT6
- 10 Gbps max transmission rate
- 500 MHz
CAT7
- individual wire pair shielding
- useful in high EMI environments
- supports 10GBASE-T standard
- larger/heavier cables
- 10 Gbps (100m) max transmission rate
- 600 MHz
fiber optic cables
- transmit light instead of electrical signals
- not susceptible to EMI
- signal travels longer distances
- multiple channels carried in single fiber
- no possibility of sparks
- lightweight
- difficult to eavesdrop
SMF
- single mode fiber
- smaller diameter
- supports greater distances
- more expensive
MMF
- multi mode fiber
- larger diameter
- supports shorter distances
- less expensive
ST fiber connector
- straight-tip
- spring loaded male/female connectors
- round elongated connector
- commonly used with MMF
SC fiber connector
- subscriber/standard connector
- snap-in connector
- somewhat square shaped
LC fiber connector
- local connector
- snap-in connector
- smaller than SC
- commonly used with SMF
SFP fiber connector
- small form factor pluggable
- small network transceiver used with copper/fiber cabling with speeds normally around 1 Gbps
- 1 end plugs directly into an SFP port on network device
- copper/fiber cable plugs into other side of transceiver using RJ-45/LC connector
- SFP+ transceivers commonly used for 10 Gigabit ethernet network links
- quad small form factor pluggable (QSFP) transceivers have 4 transmit/receive channels for use on networks up to 100 Gbps
NICs
- most computers have a wired NIC embedded on motherboard
- servers often have multiple onboard NICs
- must support network topology
- must include correct connector sockets
- must support correct speeds
MAC address
- media access control
- physical address
- layer 2 addresses
- 48-bit hexadecimal hardware address
- hardware unique identifier used only on the LAN
- must know MAC address of default gateway to communicate outside of LAN
- MAC address filtering
commands to find MAC address
- ipconfig /all (Windows)
- ifconfig (Linux)
WoL (NIC feature)
- wake on LAN
- must be supported by BIOS/UEFI
- enables powered down system to fill enough power to NIC to be woken remotely
PXE (NIC feature)
- preboot execution environment
- works with BIOS/UEFI boot sequence to enable network boot
- small OS image gets pulled across the network from PXE boot server to local RAM
- works best with DHCP
NIC teaming
- group multiple NICs together
- aggregate bandwidth of multiple NICs for increased performance
- redundancy if 1 NIC fails
- can be function of a server OS/network switch
port aggregation
configure on switch ports the server NICs are plugged into
network switches
- twisted pair cabling connects devices to wall jacks
- wall jacks use short patch cables to connect to switch ports
- multiple switches may be trunked together via a straight-through/crossover cable
VLANs
- all physical switch ports are configured within the same VLAN by default
- group devices together so they can communicate as if they were on the same physical LAN
- router is needed for devices on different VLANs to communicate
- layer 3 switches have build in routing capabilities
- may simply group switch ports together
- configuring VLAN creates a new broadcast domain
- increase security by segmenting network
configuring VLANs
- having switch examine the IP address of the connected device to determine which network it is on
- MAC address control
- control via protocol used on client device
- control by higher level applications
layer 2/3 switches
- layer 2 switches work with MAC addresses
- layer 3 switches have IP routing capabilities
- switch has its own memory
- tracks which device MAC addresses are connected to each port
- managed switches allow configuration
common switch configurations
- port duplex mode/speed
- VLANs
- disabled (unused) switch ports
- TCP/IP settings (managed switches)
- port aggregation (NIC teaming)
- port multicast support
routers
- have at least 2 interfaces that connect networks
- stores routing tables in memory
- routing information protocol (RIP)
- open shortest path first (OSPF)
- layer 3 device
PAT
- port address translation
- enables many internal IP addresses to connect through a PAT router to the internet using a single public IP address
- public IP address assigned to public interface on router
- router uses unique source port number from internal sending machines to track external connections/responses
static NAT
- maps external IP addresses on NAT router to corresponding internal IP addresses
- allow inbound connections to hosts on private network
- hides true internal IP address
- 1:1 correlation between external/internal IP addresses
IP
- internet protocol
- layer 3 protocol
IPv4 addressing
- 32-bit addresses
- 8-bit groups separated by decimal (byte/octet)
- layer 3 addresses
subnet masks
- defines network/host sections of IP address
- noted as 192.168.1.0/24
- classless inter-domain routing notation (CIDR)
- trailing number indicates number of binary 1 bits in subnet mask
127.0.0.1
reserved local loopback address
private IP address ranges
- 10.0.0.0 - 10.255.255.255
- 172.16.0.0 - 172.31.255.255
- 192.168.0.0 - 192.168.255.255
public (unique) IP addresses
allocated by ISP
subnetting
- subdivides an existing network address into subnets
- enables communication between devices on each subnet
calculating subnet
(CIDR value - 2) * number of subnets
IPv6
- broadcasts aren’t used
- heavy reliance on multicasting
- IPSec support required
- 128-bit addresses
- expressed in hexadecimal
- comprised of 8 16-bit hextets
- %(number) = interface identifier
unicast
from 1 sender to 1 target
multicast
from 1 sender to a group of devices registered with a multicast listening address
anycast
- same anycast address can be configured on many network devices
- traffic is sent to nearest device interface configured with the anycast address
::1
IPv6 loopback address
fe80::883b:ced4:63f3:f297%8
link-local address
common IPv6 network prefixes
- FE80 (self-assigned link-local address)
- FF (multicast traffic)
- 2001 (global unicast address)
- FC00 (unique unicast)
IPv6 settings
- DHCPv6
- uses subnet prefix notated in CIDR instead of subnet mask
6to4
- allows IPv6 traffic over IPv4 internet
- routers on both ends must support IPv6
- routers have IPv6 address configured on internal interface
ISATAP
- intra-site automatic tunnel addressing protocol
- allows IPv6 traffic on internal IPv4 network
- IPv4 address embedded within IPv6 address
teredo
- allows IPv6 traffic over IPv4 internet via NAT
- teredo server must reside on IPv4 internet
- public teredo servers/relays available
default gateway
- router on LAN through which traffic is sent that is leaving LAN
- ensure IP address configuration uses router interface connected to internal network
- use correct subnet mask
DNS servers
- devices need to be configured with at least 1 DNS server
- at least 2 is better
- ipconfig /all shows DNS servers
- nslookup command (Windows/Linux) to test connectivity to DNS servers
- hosts file was used to resolve names before DNS servers became common
add DNS servers in Linux
open /etc/resolv.conf and add DNS servers
WINS servers
- Windows internet name service
- resolved NetBIOS computer names to IP address
- flat structure (no hierarchy)
DHCP exchange
- DHCP discover
- DHCP offer
- DHCP request
- DHCP acknowledgement
DHCP discover
- client sends network broadcast seeking DHCP server
- client assigns itself APIPA if fails
DHCP offer
- each DHCP server responds via broadcast with an IP address lease offer
- unicast transmission used for clients renewing lease
- client works with first offer received
DHCP request
client broadcasts acceptance of offer
DHCP acknowledgement
- DHCP server sends ACK packet to the client
- DHCP sends client TCP/IP settings
DHCP lease renewal
- time interval differs between OS versions
- generally 50% of lease
- ipconfig /all to view DHCP lease information
- cat command in Linux to view contents of DHCP lease file
TCP
- connection-oriented
- session is established before transmitting data
TCP three-way handshake
- SYN
- SYN ACK
- ACK
SYN
- initial sequence number (ISN) sent by initiator
- used to track data sent/received
SYN ACK
- sent back from target
- acknowledgement of receipt of initiator’s ISN
- includes target’s ISN
ACK
- sent by initiator
- acknowledges receipt of target’s ISN
port numbers
- port addresses
- layer 4 addresses
- 1 - 65535
- 1 - 1024 = well-known/reserved services
- netstat command to see connected port
DNS port number
TCP 53
FTP port number
TCP 20/21
FTPS port number
TCP 21
HTTP port number
TCP 80
HTTPS port number
TCP 443
IMAP4 port number
TCP 143
LDAP port number
TCP 389
POP3 port number
TCP 110
RDP port number
TCP 3389
SCP port number
TCP 22
SFTP port number
TCP 22
SMTP port number
TCP 22
SMTP port number
TCP 25
Telnet port number
TCP 23
client ports/channels
- used for network services to transmit data back to clients
- always above 1024
UDP
- connectionless
- used when timing is crucial
- VoIP
- streaming apps
- multi user gaming
- DNS queries
NTP port number
UDP 123
DNS port number
UDP 53
SNMP port number
UDP 161
TFTP port number
UDP 69