Web Management Guide-R03
Table Of Contents
- How to Use This Guide
- Contents
- Figures
- Tables
- Getting Started
- Web Configuration
- Basic Management Tasks
- Displaying System Information
- Displaying Hardware/Software Versions
- Configuring Support for Jumbo Frames
- Displaying Bridge Extension Capabilities
- Managing System Files
- Setting the System Clock
- Configuring the Console Port
- Configuring Telnet Settings
- Displaying CPU Utilization
- Displaying Memory Utilization
- Resetting the System
- Interface Configuration
- VLAN Configuration
- Address Table Settings
- Spanning Tree Algorithm
- Congestion Control
- Class of Service
- Quality of Service
- VoIP Traffic Configuration
- Security Measures
- AAA Authorization and Accounting
- Configuring User Accounts
- Web Authentication
- Network Access (MAC Address Authentication)
- Configuring HTTPS
- Configuring the Secure Shell
- Access Control Lists
- Setting A Time Range
- Showing TCAM Utilization
- Setting the ACL Name and Type
- Configuring a Standard IPv4 ACL
- Configuring an Extended IPv4 ACL
- Configuring a Standard IPv6 ACL
- Configuring an Extended IPv6 ACL
- Configuring a MAC ACL
- Configuring an ARP ACL
- Binding a Port to an Access Control List
- Configuring ACL Mirroring
- Showing ACL Hardware Counters
- ARP Inspection
- Filtering IP Addresses for Management Access
- Configuring Port Security
- Configuring 802.1X Port Authentication
- DoS Protection
- IP Source Guard
- DHCP Snooping
- Basic Administration Protocols
- Configuring Event Logging
- Link Layer Discovery Protocol
- Power over Ethernet
- Simple Network Management Protocol
- Configuring Global Settings for SNMP
- Setting the Local Engine ID
- Specifying a Remote Engine ID
- Setting SNMPv3 Views
- Configuring SNMPv3 Groups
- Setting Community Access Strings
- Configuring Local SNMPv3 Users
- Configuring Remote SNMPv3 Users
- Specifying Trap Managers
- Creating SNMP Notification Logs
- Showing SNMP Statistics
- Remote Monitoring
- Switch Clustering
- IP Configuration
- IP Services
- Multicast Filtering
- Overview
- Layer 2 IGMP (Snooping and Query)
- Configuring IGMP Snooping and Query Parameters
- Specifying Static Interfaces for a Multicast Router
- Assigning Interfaces to Multicast Services
- Setting IGMP Snooping Status per Interface
- Filtering Multicast Data at Interfaces
- Displaying Multicast Groups Discovered by IGMP Snooping
- Displaying IGMP Snooping Statistics
- Filtering and Throttling IGMP Groups
- MLD Snooping (Snooping and Query for IPv6)
- Multicast VLAN Registration
- Basic Management Tasks
- Appendices
- Glossary
- Index
Chapter 12
| Security Measures
DHCP Snooping
– 346 –
DHCP Snooping
The addresses assigned to DHCP clients on insecure ports can be carefully
controlled using the dynamic bindings registered with DHCP Snooping (or using
the static bindings configured with IP Source Guard). DHCP snooping allows a
switch to protect a network from rogue DHCP servers or other devices which send
port-related information to a DHCP server. This information can be useful in
tracking an IP address back to a physical port.
Command Usage
DHCP Snooping Process
◆ Network traffic may be disrupted when malicious DHCP messages are received
from an outside source. DHCP snooping is used to filter DHCP messages
received on a non-secure interface from outside the network or fire wall. When
DHCP snooping is enabled globally and enabled on a VLAN interface, DHCP
messages received on an untrusted interface from a device not listed in the
DHCP snooping table will be dropped.
◆ Table entries are only learned for trusted interfaces. An entry is added or
removed dynamically to the DHCP snooping table when a client receives or
releases an IP address from a DHCP server. Each entry includes a MAC address,
IP address, lease time, VLAN identifier, and port identifier.
◆ The rate limit for the number of DHCP messages that can be processed by the
switch is 100 packets per second. Any DHCP packets in excess of this limit are
dropped.
◆ When DHCP snooping is enabled, DHCP messages entering an untrusted
interface are filtered based upon dynamic entries learned via DHCP snooping.
◆ Filtering rules are implemented as follows:
■
If the global DHCP snooping is disabled, all DHCP packets are forwarded.
■
If DHCP snooping is enabled globally, and also enabled on the VLAN where
the DHCP packet is received, all DHCP packets are forwarded for a trusted
port. If the received packet is a DHCP ACK message, a dynamic DHCP
snooping entry is also added to the binding table.
■
If DHCP snooping is enabled globally, and also enabled on the VLAN where
the DHCP packet is received, but the port is not trusted, it is processed as
follows:
■
If the DHCP packet is a reply packet from a DHCP server (including
OFFER, ACK or NAK messages), the packet is dropped.
■
If the DHCP packet is from a client, such as a DECLINE or RELEASE
message, the switch forwards the packet only if the corresponding
entry is found in the binding table.