Networking and Hybrid Flashcards
What services does DCHP provide to a client?
IP address, subnet mask, default gateway. Also DNS servers. Netbios name server, NTP
At what network layer does DHCP start its communicaiton?
Layer 2
Are DHCP option sets changeble once implemented?
No, immutable
How many VPCs can DHCP option sets be associated with?
0 to many
How many DHCP option sets can VPC have?
0 or 1
Are changes to DHCP option sets immediate?
Yes, but client DHCP renew takes time
Can you provide your own EC2 domain names using DHCP option sets?
Yes, you have to configure your own custom domains and DNS servers and add config to the option set
What is the default gateway for an AWS DHCP option set?
VPC router (subnet +1)
What is the default DNS server in an AWS DHCP option set?
R53 resolver (VPC +2)
Is the VPC router HA?
Yes, it is highly available across the region when you provision a VPC
How does the VPC router participate in each subnet?
It has an interface in each subnet, which is the subnet +1 address and is the default gateway in a DHCP option set.
How do you configure the behavior of the VPC router?
By using route tables
At what level of the VPC do route tables work?
Trick quesiton: They are defined at the VPC level, but associated to a subnet
Can a subnet be associated to more than one route table at a time?
No
Explain how the default route table works
Created at the time of the VPC, associated with all subnets
If a route table has two paths to a destination, how does it select the route it will use?
Selects the most specific path first.
Name on other time route tables can be associated with
Gateways
What does target = local mean on a route table
in the current VPC
What is always in the route table and uneditable?
The local route
What is the primary concern with using stateless firewalls?
You have to account for both incoming and outgoing connections of a communication chain. Often means you have to allow all outbound to ephemeral ports.
Where do NACLs fit in the VPC hierarchy?
They operate at the subnet boundary…things coming into the subnet and things going out
What two sets of rules do NACLs have?
Inbound
Outbound
NACLs allow both of what
Explicit Allows Explicit Denies (different that SGs)
Explain NACL rule evaluation
First it selects direction
Then it starts with the lowest rule number
Stops at first match
What is the catch all rule in NACLs?
a * that catches everything and Denies
NACL screen shot
Default NACL
Rule 100 that allows all
Catch all that Denies if that first rule didn’t exist.
At what level are NACLs defined?
At the VPC level, but are associated with different subnets. A subnet can have one NACL assoicated at a time. A NACL can be assigned to many subnest in the VPC.
Can you use AWS logical resources in NACLs?
No, only IPs, IP ranges, and ports.
What can you not do with SGs
You cannot explicitly deny traffic with SGs
What can you do with SGs that you can’t do with NACls?
You can apply them to enis
You can use IP/cidr ranges…and AWS logical resources…and reference other SGs…and reference yourself!