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Option 82 Field Content

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IP Routing Features Configuring DHCP Relay Switch Client Client Client Switch Client Client Relay Agent "1" VLAN 3 VLAN 4 Option 82 Enabled Switch Switch VLAN 3 VLAN 2 No Option 82 Relay Agent "2" VLAN 1 VLAN 2 Option 82 Enabled Relay Agent "3" Switch DHCP Option 82 Server Client Client Client Relay Agent 1 adds an Option 82 field to a client request, and then forwards the request toward the server. This includes any client requests received from Relay Agent 2 without an Option 82 field. Note: DHCP Option 82 does not operate with clients on VLAN 4 because DHCP requests from these clients are not routed. Relay Agent 2 does not add an Option 82 field to client requests before forwarding the requests. However, any client requests received from Relay Agent 3 will be forwarded with the Option 82 fields that were added by Relay Agent 3. Relay Agent 3 adds an Option 82 field to a client request and then forwards the request. Figure 3-22. Example of DHCP Option 82 Operation in a Network with a Non-Compliant Relay Agent Option 82 Field Content The Remote ID and Circuit ID subfields comprise the Option 82 field a relay agent appends to client requests. A DHCP server configured to apply a different IP addressing policy to different areas of a network uses the values in these subfields to determine which DHCP policy to apply to a given client request. ■ Remote ID: This configurable subfield identifies a policy area that comprises either the routing switch as a whole (by using the routing switch MAC address) or an individual VLAN configured on the routing switch (by using the IP address of the VLAN receiving the client request). • Use the IP address option if the server will apply different IP addressing policies to DHCP client requests from ports in different VLANs on the same routing switch. • Use the Management VLAN option if a Management VLAN is config ured and you want all DHCP clients on the routing switch to use the same IP address. (This is useful if you are applying the same IP addressing policy to DHCP client requests from ports in different VLANs on the same routing switch.) Configuring this option means the Management VLAN's IP address appears in the remote ID subfield of all DHCP requests originating with clients connected to the routing switch, regardless of the VLAN on which the requests originate. • Use the MAC address option if, on a given routing switch, it does not matter to the DHCP server which VLAN is the source of a client request (that is, use the MAC address option if the IP addressing 3-52

Section	Page
HP ProCurve 6120G/XG Switch 6120XG Switch Multicast and Routing Guide	1
Front Cover	1
Title Page	3
Copyright, Notices, & Publication Data	4
Contents	5
Feature Index	12
1. Getting Started	17
Contents	17
Introduction	18
Conventions	18
Command Syntax Statements	18
Command Prompts	19
Screen Simulations	19
Configuration and Operation Examples	19
Keys	19
Sources for More Information	20
Getting Documentation From the Web	22
Online Help	22
Menu Interface	22
Command Line Interface	23
Web Browser Interface	23
Need Only a Quick Start?	24
IP Addressing	24
To Set Up and Install the Switch in Your Network	25
Physical Installation	25
2. Multimedia Traffic Control with IP Multicast (IGMP)	27
Contents	27
Overview	28
IGMP General Operation and Features	29
IGMP Terms	30
IGMP Operating Features	31
Basic Operation	31
Enhancements	31
Number of IP Multicast Addresses Allowed	32
CLI: Configuring and Displaying IGMP	33
How IGMP Operates	38
Operation With or Without IP Addressing	39
Automatic Fast-Leave IGMP	40
Forced Fast-Leave IGMP	42
Configuring Delayed Group Flush	43
Using the Switch as Querier	44
Excluding Well-Known or Reserved Multicast Addresses from IP Multicast Filtering	45
3. IP Routing Features	47
Contents	47
Overview of IP Routing	50
IP Interfaces	51
IP Tables and Caches	51
ARP Cache Table	52
IP Route Table	52
IP Forwarding Cache	53
IP Route Exchange Protocols	54
IP Global Parameters for Routing Switches	54
ARP Age Timer	55
IP Interface Parameters for Routing Switches	58
Configuring IP Parameters for Routing Switches	59
Configuring IP Addresses	59
Changing the Router ID	59
Configuring ARP Parameters	60
How ARP Works	60
Configuring Forwarding Parameters	62
Changing the TTL Threshold	62
Enabling Forwarding of Directed Broadcasts	62
Configuring ICMP	64
Disabling ICMP Messages	64
Disabling Replies to Broadcast Ping Requests	64
Disabling ICMP Destination Unreachable Messages	65
Disabling ICMP Redirects	66
Configuring Static IP Routes	66
Static Route Types	66
Other Sources of Routes in the Routing Table	67
Static IP Route Parameters	67
Static Route States Follow VLAN States	68
Configuring a Static IP Route	68
Configuring the Default Route	70
Configuring RIP	71
Overview of RIP	71
RIP Parameters and Defaults	72
RIP Global Parameters	72
RIP Interface Parameters	72
Configuring RIP Parameters	73
Enabling RIP	73
Enabling IP RIP on a VLAN	74
Changing the RIP Type on a VLAN Interface	74
Changing the Cost of Routes Learned on a VLAN Interface	74
Configuring RIP Redistribution	75
Define RIP Redistribution Filters	75
Modify Default Metric for Redistribution	76
Enable RIP Route Redistribution	76
Changing the Route Loop Prevention Method	77
Displaying RIP Information	77
Displaying General RIP Information	78
Displaying RIP Interface Information	80
Displaying RIP Peer Information	81
Displaying RIP Redistribution Information	83
Displaying RIP Redistribution Filter (restrict) Information	83
Configuring IRDP	84
Enabling IRDP Globally	85
Enabling IRDP on an Individual VLAN Interface	85
Displaying IRDP Information	87
Configuring DHCP Relay	87
Overview	87
DHCP Packet Forwarding	88
Unicast Forwarding	88
Broadcast Forwarding	88
Prerequisites for DHCP Relay Operation	88
Enabling DHCP Relay	89
Configuring a BOOTP/DHCP Relay Gateway	89
Displaying the BOOTP Gateway	90
Operating Notes	91
Configuring an IP Helper Address	91
Operating Notes	91
Verifying the DHCP Relay Configuration	91
Displaying the DHCP Relay Setting	91
Displaying DHCP Helper Addresses	92
DHCP Option 12	93
SNMP Support	93
DHCP Option 82	94
Option 82 Server Support	95
Terminology	96
General DHCP Option 82 Requirements and Operation	97
Option 82 Field Content	98
Forwarding Policies	100
Configuration Options for Managing DHCP Client Request Packets	100
Multiple Option 82 Relay Agents in a Client Request Path	101
Validation of Server Response Packets	102
Multinetted VLANs	103
Configuring Option 82	104
Example of Option 82 Configuration	106
Operating Notes	108
UDP Broadcast Forwarding	110
Overview	110
Subnet Masking for UDP Forwarding Addresses	111
Configuring and Enabling UDP Broadcast Forwarding	112
Globally Enabling UDP Broadcast Forwarding	112
Configuring UDP Broadcast Forwarding on Individual VLANs	112
Displaying the Current IP Forward-Protocol Configuration	114
Operating Notes for UDP Broadcast Forwarding	115
Messages Related to UDP Broadcast Forwarding	115
Index	117
A	117
B	117
C	117
D	117
E	118
F	118
G	118
H	118
I	118
L	119
M	119
O	119
P	119
Q	119
R	119
S	120
T	120
U	120
V	120
W	120

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IP Routing Features

Configuring DHCP Relay

Switch

Client

DHCP

Option 82

Server

Relay Agent 1

adds an Option 82 field to a

client request, and then forwards the

request toward the server. This includes

any client requests received from Relay

Agent 2 without an Option 82 field.

Note:

DHCP Option 82 does not operate

with clients on VLAN 4 because DHCP

requests from these clients are not routed.

Relay Agent 2

does not add an Option 82

field to client requests before forwarding

the requests. However, any client

requests received from Relay Agent 3 will

be forwarded with the Option 82 fields that

were added by Relay Agent 3.

Relay Agent 3

adds an Option 82 field to a

client request and then forwards the

request.

Client

Switch

Relay Agent “2”

VLAN 1

VLAN 2

VLAN 3

VLAN 2

VLAN 3

VLAN 4

Switch

Client

Switch

Client

Switch

Client

Relay Agent “1”

Relay Agent “3”

No Option 82

Option 82 Enabled

Client

Figure 3-22. Example of DHCP Option 82 Operation in a Network with a Non-Compliant Relay Agent

Option 82 Field Content

The Remote ID and Circuit ID subfields comprise the Option 82 field a relay

agent appends to client requests. A DHCP server configured to apply a

different IP addressing policy to different areas of a network uses the values

in these subfields to determine which DHCP policy to apply to a given client

request.

■

Remote ID:

This configurable subfield identifies a policy area that

comprises either the routing switch as a whole (by using the routing

switch MAC address) or an individual VLAN configured on the routing

switch (by using the IP address of the VLAN receiving the client request).

•

Use the IP address option if the server will apply different IP

addressing policies to DHCP client requests from ports in different

VLANs on the same routing switch.

•

Use the Management VLAN option if a Management VLAN is config-

ured and you want all DHCP clients on the routing switch to use the

same IP address. (This is useful if you are applying the same IP

addressing policy to DHCP client requests from ports in different

VLANs on the same routing switch.) Configuring this option means

the Management VLAN’s IP address appears in the remote ID subfield

of all DHCP requests originating with clients connected to the routing

switch, regardless of the VLAN on which the requests originate.

•

Use the MAC address option if, on a given routing switch, it does not

matter to the DHCP server which VLAN is the source of a client

request (that is, use the MAC address option if the IP addressing

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