322
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Dynamic Host Configuration Protocol
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•
DHCP Snooping on page 322
•
Dynamic ARP Inspection on page 325
•
Source Address Validation on page 327
Option 82
RFC 3046 (Relay Agent Information option, or Option 82) is used for class-based IP address assignment.
The code for the Relay Agent Information option is 82, and is comprised of two sub-options, Circuit ID
and Remote ID.
•
Circuit ID
is the interface on which the client-originated message is received.
•
Remote ID
identifies the host from which the message is received. The value of this sub-option is the
MAC address of the relay agent that adds Option 82.
The DHCP relay agent inserts Option 82 before forwarding DHCP packets to the server. The server can
use this information to:
•
track the number of address requests per relay agent; restricting the number of addresses available per
relay agent can harden a server against address exhaustion attacks.
•
associate client MAC addresses with a relay agent to prevent offering an IP address to a client spoofing
the same MAC address on a different relay agent.
•
assign IP addresses according to the relay agent. This prevents generating DHCP offers in response to
requests from an unauthorized relay agent.
The server echoes the option back to the relay agent in its response, and the relay agent can use the
information in the option to forward a reply out the interface on which the request was received rather than
flooding it on the entire VLAN.
The relay agent strips Option 82 from DHCP responses before forwarding them to the client.
DHCP Snooping
DHCP Snooping protects networks from spoofing. In the context of DHCP Snooping, all ports are either
trusted or untrusted. By default, all ports are untrusted. Trusted ports are ports through which attackers
cannot connect. Manually configure ports connected to legitimate servers and relay agents as trusted.
Task
Command Syntax
Command Mode
Insert Option 82 into DHCP packets.
For routers between the relay agent
and the DHCP server, enter the
trust-downstream
option.
ip dhcp relay information-option
[
trust-downstream
]
CONFIGURATION
Summary of Contents for Force10 E300
Page 1: ...FTOS Configuration Guide FTOS 8 4 2 7 E Series TeraScale C Series S Series S50 S25 ...
Page 32: ...32 w w w d e l l c o m s u p p o r t d e l l c o m ...
Page 132: ...132 802 1X w w w d e l l c o m s u p p o r t d e l l c o m ...
Page 310: ...310 Configuration Replace and Rollback w w w d e l l c o m s u p p o r t d e l l c o m ...
Page 330: ...330 Dynamic Host Configuration Protocol w w w d e l l c o m s u p p o r t d e l l c o m ...
Page 402: ...402 High Availability w w w d e l l c o m s u p p o r t d e l l c o m ...
Page 462: ...462 Interfaces w w w d e l l c o m s u p p o r t d e l l c o m ...
Page 482: ...482 IPv4 Addressing w w w d e l l c o m s u p p o r t d e l l c o m ...
Page 506: ...506 IPv6 Addressing w w w d e l l c o m s u p p o r t d e l l c o m ...
Page 582: ...582 Layer 2 w w w d e l l c o m s u p p o r t d e l l c o m ...
Page 642: ...642 Multicast Source Discovery Protocol w w w d e l l c o m s u p p o r t d e l l c o m ...
Page 662: ...662 Multiple Spanning Tree Protocol w w w d e l l c o m s u p p o r t d e l l c o m ...
Page 690: ...690 Object Tracking w w w d e l l c o m s u p p o r t d e l l c o m ...
Page 754: ...754 PIM Dense Mode w w w d e l l c o m s u p p o r t d e l l c o m ...
Page 784: ...784 PIM Source Specific Mode w w w d e l l c o m s u p p o r t d e l l c o m ...
Page 800: ...800 Power over Ethernet w w w d e l l c o m s u p p o r t d e l l c o m ...
Page 876: ...876 Quality of Service w w w d e l l c o m s u p p o r t d e l l c o m ...
Page 892: ...892 Routing Information Protocol w w w d e l l c o m s u p p o r t d e l l c o m ...
Page 1006: ...1006 Simple Network Management Protocol w w w d e l l c o m s u p p o r t d e l l c o m ...
Page 1018: ...1018 SONET SDH w w w d e l l c o m s u p p o r t d e l l c o m ...
Page 1048: ...1048 Broadcast Storm Control w w w d e l l c o m s u p p o r t d e l l c o m ...
Page 1096: ...1096 Uplink Failure Detection UFD w w w d e l l c o m s u p p o r t d e l l c o m ...
Page 1098: ...1098 Upgrade Procedures w w w d e l l c o m s u p p o r t d e l l c o m ...
Page 1196: ...1196 C Series Debugging and Diagnostics w w w d e l l c o m s u p p o r t d e l l c o m ...
Page 1252: ...1252 Standards Compliance w w w d e l l c o m s u p p o r t d e l l c o m ...
Page 1262: ...1262 Index w w w d e l l c o m s u p p o r t d e l l c o m ...