Podcast
Questions and Answers
What happens to DHCP messages received on an untrusted port and normally sent by a DHCP server?
What happens to DHCP messages received on an untrusted port and normally sent by a DHCP server?
- They are filtered for MAC address consistency
- They are forwarded to the client
- They are checked against the DHCP Snooping binding table
- They are discarded (correct)
Which type of DHCP messages are filtered based on MAC address consistency?
Which type of DHCP messages are filtered based on MAC address consistency?
- LEASE and DHCPACK messages
- DISCOVER and REQUEST messages (correct)
- INFORM and DHCPRELEASE messages
- RELEASE and DECLINE messages
What happens when a DHCP message results in a lease?
What happens when a DHCP message results in a lease?
- The message is discarded
- A new entry is added to the DHCP Snooping binding table (correct)
- The message is forwarded to the client
- The message is filtered for MAC address consistency
What type of ports do not filter DHCP messages?
What type of ports do not filter DHCP messages?
Why does the attacker send a DHCPOFFER message to PC1?
Why does the attacker send a DHCPOFFER message to PC1?
What happens to the packets sent by PC1 to the default gateway?
What happens to the packets sent by PC1 to the default gateway?
What is the purpose of the DHCP Snooping binding table?
What is the purpose of the DHCP Snooping binding table?
What is the result of a DHCP attack on PC1?
What is the result of a DHCP attack on PC1?
What is the main approach used by DAI to prevent ARP attacks?
What is the main approach used by DAI to prevent ARP attacks?
What is the purpose of ARP ACLs in DAI configuration?
What is the purpose of ARP ACLs in DAI configuration?
What is the purpose of DHCP Snooping binding table?
What is the purpose of DHCP Snooping binding table?
What is the default setting for ports in DAI configuration?
What is the default setting for ports in DAI configuration?
What is a key consideration when configuring DAI on a Layer 2 switch?
What is a key consideration when configuring DAI on a Layer 2 switch?
What happens when an attacker tries to lease all IP addresses in the subnet using a DHCP request?
What happens when an attacker tries to lease all IP addresses in the subnet using a DHCP request?
What is the primary function of DAI filtering?
What is the primary function of DAI filtering?
What is the purpose of the chaddr field in a DHCP message?
What is the purpose of the chaddr field in a DHCP message?
What is the purpose of the DHCP Snooping binding table in DAI configuration?
What is the purpose of the DHCP Snooping binding table in DAI configuration?
What happens when a DHCP RELEASE message is received on a different port than the original DHCP request?
What happens when a DHCP RELEASE message is received on a different port than the original DHCP request?
What is required to configure DHCP Snooping?
What is required to configure DHCP Snooping?
What is a key benefit of using ARP ACLs in DAI configuration?
What is a key benefit of using ARP ACLs in DAI configuration?
What should be configured to trust on a Layer 2 switch when configuring DAI?
What should be configured to trust on a Layer 2 switch when configuring DAI?
What is the purpose of configuring trusted ports in DHCP Snooping?
What is the purpose of configuring trusted ports in DHCP Snooping?
What is the result of an attacker attempting to lease all IP addresses in the subnet using a DHCP request?
What is the result of an attacker attempting to lease all IP addresses in the subnet using a DHCP request?
What does DHCP Snooping check in a DHCP message to prevent MAC address spoofing?
What does DHCP Snooping check in a DHCP message to prevent MAC address spoofing?
Study Notes
DHCP Snooping and Dynamic ARP Inspection
- DHCP Snooping checks
chaddr(client hardware address) and Ethernet Source MAC to prevent attacks. - An attacker can attempt to lease all IP addresses in the subnet, overwhelming the DHCP server.
- DHCP Snooping builds a binding table for legitimate DHCP clients, listing important facts such as IP addresses and MAC addresses.
Binding Table
- The binding table is used by DHCP Snooping and Dynamic ARP Inspection to make decisions.
- The table lists important facts about legitimate DHCP clients, including IP addresses and MAC addresses.
DHCP Snooping Logic
- DHCP Snooping discards DHCP RELEASE messages if the incoming interface and IP address do not match the binding table entry.
- The process involves comparing the incoming message, interface, and matching table entry.
DHCP Snooping Configuration
- DHCP Snooping requires two global commands: one to enable DHCP Snooping and one to list the VLANs on which to use DHCP Snooping.
- Trusted ports must be configured for DHCP Snooping to operate.
Dynamic ARP Inspection
- DAI filtering is based on the DHCP Snooping binding table.
- DAI checks for source MAC addresses and confirms ARP correctness based on DHCP Snooping data.
- DAI can also use statically configured ARP ACLs for ports connected to devices with static IP addresses.
DAI Configuration
- Before configuring DAI, decisions must be made about using DHCP Snooping, ARP ACLs, or both.
- DHCP Snooping must be configured, and trusted ports must be selected.
- DAI must be enabled on select VLANs and ports.
Summary of Rules for DHCP Snooping
- DHCP messages received on untrusted ports from servers are discarded.
- DHCP messages received on untrusted ports from clients may be filtered if they appear to be part of an attack.
- DHCP messages received on trusted ports are forwarded without filtering.
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Description
This quiz covers how DHCP snooping checks chaddr and Ethernet Source MAC to prevent attacks on DHCP servers. Learn how to filter DISCOVER messages based on MAC addresses and protect your network.
