Contents

Configuring MAC address learning through a Layer 3 device· 1

About MAC address learning through a Layer 3 device· 1

Working mechanism·· 1

Entry aging· 1

Restrictions and guidelines: MAC address learning through a Layer 3 device configuration· 1

MAC address learning through a Layer 3 device configuration tasks at a glance· 2

Prerequisites· 2

Enabling ARP entry synchronization through SNMP· 2

Configuring the target Layer 3 device· 2

Setting the parameters for ARP entry synchronization· 3

Display and maintenance commands for MAC address learning through a Layer 3 device· 3

MAC address learning through a Layer 3 device configuration examples· 3

Example: Configuring MAC address learning through a Layer 3 device· 3

 

Configuring MAC address learning through a Layer 3 device

About MAC address learning through a Layer 3 device

This feature enables the device to learn the MAC address of a terminal (a PC for example) when a Layer 3 device exists between the device and the terminal through SNMP for network traffic control.

Working mechanism

Figure 1 MAC address learning through a Layer device workflow

 

As shown in Figure 1, MAC address learning through a Layer 3 device proceeds as follows:

1.     The gateway learns the IP-MAC binding of the terminal, and then generates an ARP entry.

2.     The device sends SNMP requests to the gateway at the specified intervals to request the ARP entry.

3.     The gateway sends a response that contains the ARP entry to the device.

4.     Upon receiving the response, the device saves the ARP entry in the memory. Then it can learn the MAC address of the terminal.

Entry aging

ARP entries learned through a Layer 3 device will be automatically deleted when the aging timer expires, or can be cleared using the reset snmp-server arp-sync table command.

Restrictions and guidelines: MAC address learning through a Layer 3 device configuration

·     ARP entries learned using this feature can be used only for policy packet filtering and cannot be used for packet forwarding.

·     Only MAC addresses mapped from IPv4 addresses can be learned.

·     Make sure no NAT devices exist between the device and the Layer 3 device.

·     This feature is not applicable to a VRF network.

MAC address learning through a Layer 3 device configuration tasks at a glance

To configure MAC address learning through a Layer 3 device, perform the following tasks:

1.     Enabling ARP entry synchronization through SNMP

2.     Configuring the target Layer 3 device

3.     (Optional.) Setting the parameters for ARP entry synchronization

Prerequisites

Make sure SNMP agent has been enabled and a community name has been configured on the Layer 3 device. For information about SNMP, see SNMP configuration in Network Management and Monitoring.

Enabling ARP entry synchronization through SNMP

About this task

With this feature enabled, the device acts as an NMS to learn all ARP entries on a Layer 3 device (agent) to obtain the MAC address of the Layer 3 device.

Procedure

1.     Enter system view.

system-view

2.     Enable ARP entry synchronization through SNMP.

snmp-server arp-sync enable

By default, ARP entry synchronization through SNMP is disabled.

Configuring the target Layer 3 device

1.     Enter system view.

system-view

2.     Configure the target Layer 3 device for ARP entry synchronization through SNMP.

SNMP v2c:

snmp-server arp-sync target-host address ip-address community { simple | cipher } community-name v2c

SNMP v3:

snmp-server arp-sync target-host address ip-address usm-user v3 user-name [ { simple | cipher } authentication-mode { md5 | sha } auth-password [ privacy-mode { aes128 | des56 } pri-password ] ]

By default, no target Layer 3 device is configured for ARP entry synchronization through SNMP.

Setting the parameters for ARP entry synchronization

About this task

With this feature configured, the device sends SNMP requests for ARP entry synchronization to the target Layer 3 device at the specified intervals. If the device does not receive an SNMP response before the timeout expires within the specified interval, the device re-sends SNMP requests.

Procedure

1.     Enter system view.

system-view

2.     Set the parameters for ARP entry synchronization.

snmp-server arp-sync { interval interval | timeout time } *

By default, the interval for sending SNMP requests is 5 seconds and the timeout for SNMP responses is 3 seconds.

Display and maintenance commands for MAC address learning through a Layer 3 device

Execute display commands in any view and reset commands in user view.

 

Task	Command
Display the ARP entries synchronized through SNMP.	display snmp-server arp-sync table
Clear the ARP entries synchronized through SNMP.	reset snmp-server arp-sync table

 

MAC address learning through a Layer 3 device configuration examples

Example: Configuring MAC address learning through a Layer 3 device

Network configuration

As shown in Figure 2, hosts in an internal network are connected to the device through a Layer 3 gateway and the device is connected to the Internet.

·     Configure MAC address learning through a Layer 3 device to ensure that the device can learn the MAC addresses of the hosts through the gateway.

·     Configure security policies by using the learned MAC addresses to allow only Host A and Host B to access the Internet.

Figure 2 Network diagram

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Procedure

1.     Configure the gateway:

# Specify an IP address for each interface and configure routing features to ensure network reachability. (Details not shown.)

# Configure SNMPv2c, and create the read-only community with the plaintext form name public.

<Gateway> system-view

[Gateway] snmp-agent sys-info version v2c

[Gateway] snmp-agent community read simple public

2.     Configure the device:

a.     Assign IP addresses to interfaces:

# Assign an IP address to interface GigabitEthernet 1/0/1.

<Device> system-view

[Device] interface gigabitethernet 1/0/1

[Device-GigabitEthernet1/0/1] ip address 2.2.2.2 255.255.255.0

[Device-GigabitEthernet1/0/1] quit

# Assign IP addresses to other interfaces in the same way. (Details not shown.)

b.     Configure settings for routing.

This example configures static routes, and the next hop in the route to the Internet is 3.3.3.1.

[Device] ip route-static 1.1.1.0 24 2.2.2.1

[Device] ip route-static 0.0.0.0 0 3.3.3.1

c.     Add interfaces to security zones.

[Device] security-zone name trust

[Device-security-zone-Trust] import interface gigabitethernet 1/0/1

[Device-security-zone-Trust] quit

[Device] security-zone name untrust

[Device-security-zone-Untrust] import interface gigabitethernet 1/0/2

[Device-security-zone-Untrust] quit

d.     Configure a security policy.

# Configure a rule named rule1 to allow the device to access the gateway.

[Device] security-policy ip

[Device-security-policy-ip] rule name rule1

[Device-security-policy-ip-0-rule1] source-zone local

[Device-security-policy-ip-0-rule1] destination-zone trust

[Device-security-policy-ip-0-rule1] source-ip-host 2.2.2.2

[Device-security-policy-ip-0-rule1] destination-ip-host 2.2.2.1

[Device-security-policy-ip-0-rule1] action pass

[Device-security-policy-ip-0-rule1] quit

# Configure a rule named rule2 to permit traffic only from MAC object group groupmac to the Internet.

[Device-security-policy-ip] rule name rule2

[Device-security-policy-ip-1-rule2] source-zone trust

[Device-security-policy-ip-1-rule2] destination-zone untrust

[Device-security-policy-ip-1-rule2] source-mac groupmac

[Device-security-policy-ip-1-rule2] action pass

[Device-security-policy-ip-1-rule2] quit

# Activate rule matching acceleration.

[Device-security-policy-ip] accelerate enhanced enable

[Device-security-policy-ip] quit

e.     Configure MAC address learning through the gateway.

Enable ARP entry synchronization through SNMP. Configure the device to synchronize ARP entries from the gateway.

[Device] snmp-server arp-sync enable

[Device] snmp-server arp-sync target-host address 2.2.2.1 community simple public v2c

[Device] snmp-server arp-sync interval 10 timeout 4

f.     Create a MAC object group named groupmac. Add Host A's MAC address 00e0-0000-0001 and Host B's MAC address 00e0-0000-0002 to the group.

[Device] object-group mac-address groupmac

[Device-obj-grp-mac-groupmac] mac 00e0-0000-0001

[Device-obj-grp-mac-groupmac] mac 00e0-0000-0002

[Device-obj-grp-mac-groupmac] quit

Verifying the configuration

1.     Verify that ARP entries have been synchronized to the device.

[Device] display snmp-server arp-sync table

IP Address       MAC Address        Aging(M)

1.1.1.1          00e0-0000-0001     1

1.1.1.2          00e0-0000-0002     1

1.1.1.3          00e0-0000-0003     1

Total:3

2.     Verify that Host A and Host B can access the external network but Host C cannot.