DHCP & Multilayer Switches

Question 1

Briefly describe the DHCP handshake.

Answer 1

1.Host sends discovery broadcast. 2.Server replies with offer broadcast. 3.Host replies with a request broadcast. 4.Server responds with an ACK broadcast.

Question 2

What is a requirement for each subnet that a Cisco device is handing out?

Answer 2

The device must have an IP in that subnet on either a SVI, sub interface, or physical interface.

Question 3

On Cisco devices, how are DHCP exclusions configured?

Answer 3

Manually, via the global-config context.

Question 4

What IPs must be excluded in a DHCP range?

Answer 4

All that you need, including the IP residing on the Cisco device.

Question 5

Briefly describe how to configure a DHCP pool.

Answer 5

1.Create the pool with the “ip dhcp pool” command. 2.Set your range with the “network” command. 3.Configure your default router. 4.Configure your DNS server. 5.Configure your domain name. 6.Configure your lease time.

Question 6

What is a DHCP helper address?

Answer 6

The address of a DHCP server, configured on a SVI, sub interface, or physical interface. It relays DHCP messages to out-of-network servers.

Question 7

How many DHCP helper addresses can be configured on an interface?

Answer 7

As many as you want. The first one will be used, if it’s unreachable the device will move to the next one in the list.

Question 8

Can you configure static IPs in a Cisco DHCP pool?

Answer 8

Yes, with the “host” and “client-identifier” commands.

Question 9

What command establishes a DHCP relay to another network?

Answer 9

(if)ip helper-address IP

Question 10

What is the DHCP DORA process?

Answer 10

Discover (any servers), Offer (address info), Request (to use the offer), ACK (that its ok to use the offer).

Question 11

What 5 basic commands are needed to configure DHCP on a multilayer switch?

Answer 11

ip dhcp exclude-address START ENDip dhcp pool NAMEnetwork IP MASKdefault-router IP1 IP2 IP3 etc…lease [infinite, D H M)

Question 12

What are the 4 steps in DHCP negotiation?

Answer 12

1-client sends DHCP discover as broadcast, 2-DHCP server sends DHCP offer, client sends DHCP Request, DHCP server sends DHCP ack

Question 13

How do you configure a DHCP gateway?

Answer 13

first configure a L3 interface in same VLAN as clients, then use the ip helper-address command to ID the DHCP server

Question 14

What data does DHCP snooping track?

Answer 14

completed dhcp bindings, mac addresses, IP addresses, etc.

Question 15

How is DHCP snooping enabled (scope)?

Answer 15

globally

Question 16

When DHCP snooping is turned on, by default, it considers all ports ______

Answer 16

untrusted

Question 17

How does adding option-82 to DHCP snooping affect things?

Answer 17

The switch adds its MAC to the option 82 field so that the DHCP reply echoes back the switch’s own information

Question 18

what is dhcp snooping rate limiting?

Answer 18

Limits the number if dhcp requests on a port\

Question 19

What are spoofed addresses?

Answer 19

They disguise the origin of an attack