H3C S5500-SI Series User manual

Operation Manual – ARP
H3C S5500-SI Series Ethernet Switches Table of Contents
i
Table of Contents
Chapter 1 ARP Configuration....................................................................................................... 1-1
1.1 ARP Overview....................................................................................................................1-1
1.1.1 ARP Function..........................................................................................................1-1
1.1.2 ARP Message Format.............................................................................................1-1
1.1.3 ARP Process...........................................................................................................1-2
1.1.4 ARP Mapping Table................................................................................................1-3
1.2 Configuring ARP................................................................................................................1-4
1.2.1 Adding a Static ARP Entry...................................................................................... 1-4
1.2.2 Setting the Maximum Number of ARP Entries for a VLAN Interface...................... 1-4
1.2.3 Setting Aging Time for Dynamic ARP Entries.........................................................1-5
1.2.4 Enabling the ARP Entry Check...............................................................................1-5
1.2.5 ARP Configuration Example ................................................................................... 1-5
1.3 Configuring Gratuitous ARP .............................................................................................. 1-6
1.3.1 Introduction to Gratuitous ARP ...............................................................................1-6
1.3.2 Configuring Gratuitous ARP....................................................................................1-6
1.4 Displaying and Maintaining ARP.......................................................................................1-7
Chapter 2 Proxy ARP Configuration............................................................................................ 2-1
2.1 Proxy ARP Overview.........................................................................................................2-1
2.2 Enabling Proxy ARP..........................................................................................................2-1
2.3 Displaying and Maintaining Proxy ARP.............................................................................2-2
2.4 Proxy ARP Configuration Example.................................................................................... 2-2
2.4.1 Proxy ARP Configuration Example.........................................................................2-2
2.4.2 Local Proxy ARP Configuration Example in Case of Port Isolation........................2-3
2.4.3 Local Proxy ARP Configuration Example in Isolate-user-vlan................................2-4

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H3C S5500-SI Series Ethernet Switches Chapter 1 ARP Configuration
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Chapter 1 ARP Configuration
When configuringARP, go to these sections for information you are interested in:
zARP Overview
zConfiguring ARP
zConfiguring Gratuitous ARP
zDisplaying and MaintainingARP
1.1 ARP Overview
1.1.1 ARP Function
Address resolution protocol (ARP) is used to resolve an IP address into a MAC
address.
An IP address is the address of a host at the network layer. To send a network layer
packet to a destination host, the device must know the MAC address of the destination
host. To this end, the IP address must be resolved into the corresponding MAC
address.
1.1.2 ARP Message Format
2211
24664
Hardware addresslength
Protocol addresslength
28-byte ARP request/response
Protocol
type
Hardware
type OP Sender hardware address Sender protocol address Targethardware
address
Target
protocol
address
t Figure 1-1 ARP message forma
The following explains the fields in Figure 1-1.
zHardware type: This field specifies the type of a hardware address. The value “1”
represents an Ethernet address.
zProtocol type: This field specifies the type of the protocol address to be mapped.
The hexadecimal value “0x0800” represents an IP address.
zHardware address length and protocol address length: They respectively specify
the length of a hardware address and a protocol address, in bytes. For an Ethernet

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address, the value of the hardware address length field is "6”. For an IP(v4)
address, the value of the protocol address field is “4”.
zOP: Operation code. This field specifies the type of ARP message. The value “1”
represents an ARP request and “2” represents an ARP reply.
zSender hardware address: This field specifies the hardware (MAC) address of the
device sending the message.
zSender protocol address: This field specifies the IP address of the device sending
the message.
zTarget hardware address: This field specifies the hardware address of the device
the message is being sent to.
zTarget protocol address: This field specifies the IP address of the device the
message is being sent to.
1.1.3 ARP Process
Host A
192 .168 . 1. 1
0002 .6779 .0 f4 c
Host B
192 . 168 . 1 .2
00 a0 .2470 .febd
Source MAC address
0002 .6779 .0 f 4c 192 . 168 . 1 .1
00 a 0 .2470 .febd 192 . 168 . 1 .2 0002 .6779 .0f 4c 192 . 168
192 .16800 a 0 .2470 .febd
Source IP address Destination MAC address Destination IP
Destination IPDestination MAC addressSource IP addressSource MAC address . 1 .1
. 1. 2
address
address
s Figure 1-2 ARP proces
Suppose that Host A and Host B are on the same subnet and that Host A sends a
message to Host B. The resolution process is as follows:
1) Host A looks in its ARP mapping table to see whether there is an ARP entry for
Host B. If Host A finds it, Host A uses the MAC address in the entry to encapsulate
the IP packet into a data link layer frame and sends the frame to Host B.
2) If Host A finds no entry for Host B, Host A buffers the packet and broadcasts an
ARP request, in which the source IP address and source MAC address are
respectively the IP address and MAC address of Host A and the destination IP
address and MAC address are respectively the IP address of Host B and an
all-zero MAC address. As ARP request packet is broadcast, an ARP request
packet is received by all the hosts in the network segment. However, only the
intended host (host B) processes and responds to it.
3) Host B compares its own IP address with the destination IP address in the ARP
request. If they are the same, Host B saves the source IP address and source

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MAC address into its ARP mapping table, encapsulates its MAC address into an
ARP reply, and unicasts the reply to Host A.
4) After receiving the ARP reply, Host A adds the MAC address of Host B into its ARP
mapping table for subsequent packet forwarding. Meanwhile, Host A
encapsulates the IP packet and sends it out.
Note:
When Host A and Host B are not on the same subnet, Host A first sends an ARP
request to the gateway. The destination IP address in the ARP request is the IP
address of the gateway. After obtaining the MAC address of the gateway from an ARP
reply, Host A encapsulates the packet and sends it to the gateway. Subsequently, the
gateway broadcasts the ARP request, in which the destination IP address is the one of
Host B. After obtaining the MAC address of Host B from another ARP reply, the
gateway sends the packet to Host B.
1.1.4 ARP Mapping Table
After obtaining the destination MAC address, the device adds the IP address to MAC
address mapping into its own ARP mapping table, for forwarding packets with the same
destination in future.
ARP entries fall into two categories: dynamic and static.
1) A dynamic entry is automatically created and maintained by ARP. It can get aged,
be updated by a new ARP packet, or be overwritten by a static ARP entry. When
the aging timer expires or the interface goes down, the corresponding dynamic
ARP entry will be removed.
2) A static ARP entry is manually configured and maintained. It cannotget aged or be
overwritten by a dynamic ARP entry. It can be permanent or non-permanent.
zA permanent static ARP entry can be directly used to forward data. When
configuring a permanent static ARP entry, you must configure a VLAN and
outbound port for the entry besides the IP address and MAC address.
zA non-permanent static ARP entry cannot be directly used for forwarding data.
When configuring a non-permanent static ARP entry, you only need to configure
the IP address and MAC address. When forwarding IP packets, the device sends
an ARP request. If the source IP and MAC addresses in the received ARP reply
are the same as the configured IP and MAC addresses, the device adds the port
receiving the ARP reply into the static ARP entry. Now the entry can be used for
forwarding IP packets.

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Note:
Usually ARP dynamically implements and automatically seeks mappings from IP
addresses to MAC addresses, without manual intervention.
1.2 Configuring ARP
1.2.1 Adding a Static ARP Entry
Follow these steps to add a staticARP entry:
To do… Use the command… Remarks
Enter system view system-view —
Configure a permanent
static ARP entry
arp static ip-address
mac-address [ vlan-id
interface-type
interface-number ]
Required
No permanent static ARP
entry is configured by
default.
Configure a
non-permanent static
ARP entry
arp static ip-address
mac-address
Required
No non-permanent static
ARP entry is configured
by default.
Caution:
zA static ARP mapping is effective when the device works normally. However, when
a VLAN or VLAN interface is deleted, the corresponding ARP entries will be deleted
accordingly.
zThe vlan-id argument must be the ID of an existing VLAN which corresponds to the
ARP entries. In addition, the Ethernet port following the argument must belong to
that VLAN. A VLAN interface must be created for the VLAN.
1.2.2 Setting the Maximum Number of ARP Entries for a VLAN Interface
Follow these steps to set the maximum number of dynamic ARP entries that a VLAN
interface can learn:
To do… Use the command… Remarks
Enter system view system-view —

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To do… Use the command… Remarks
Enter VLAN interface
view interface vlan-interface
vlan-id —
Set the maximum number
of dynamic ARP entries
that a VLAN interface can
learn
arp max-learning-num
number Optional
2048 by default
1.2.3 Setting Aging Time for Dynamic ARP Entries
After dynamic ARP entries expire, the system will delete them from the ARP mapping
table. You can adjust the aging time for dynamic ARP entries according to the actual
network condition.
Follow these steps to set aging time for dynamic ARP entries:
To do… Use the command… Remarks
Enter system view system-view —
Set aging time for
dynamic ARP entries arp timer aging
aging-time Optional
20 minutes by default
1.2.4 Enabling the ARP Entry Check
ARP entrycheck function is used to control multicast MAC address learning. By default,
it is enabled on an S5500-SI Ethernet switch. That is, the switches do not learn
multicast MAC addresses. Multicast MAC learning is enabled once the ARP entry
check function is disabled.
Follow these steps to enable the ARP entry check:
To do… Use the command… Remarks
Enter system view system-view —
Enable the ARP entry
check arp check enable Optional
Enabled by default
1.2.5 ARP Configuration Example
I. Network requirement
zEnable the ARP entry check.
zSet the aging time for dynamic ARP entries to 10 minutes.

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zAdd an ARPentry, with the IP address being 192.168.1.1, the MAC address being
00e0-fc01-0000, and the outbound interface being GigabitEthernet1/0/2 of VLAN
10.
II. Configuration procedure
<Sysname> system-view
[Sysname] arp check enable
[Sysname] arp timer aging 10
[Sysname] vlan 10
[Sysname-vlan10] quit
[Sysname] interface vlan-interface 10
[Sysname- vlan-interface10] quit
[Sysname] interface GigabitEthernet 1/0/2
[Sysname-GigabitEthernet1/0/2] port access vlan 10
[Sysname-GigabitEthernet1/0/2] quit
[Sysname] arp static 192.168.1.1 00e0-fc01-0000 10 GigabitEthernet1/0/2
1.3 Configuring Gratuitous ARP
1.3.1 Introduction to Gratuitous ARP
A gratuitous ARP packet is a special ARP packet, in which the source IP address and
destination IP address are both the IP address of the sender.
A device can implement the following functions by sending gratuitousARP packets:
zDetermining whether its IP address is already used by another device.
zInforming other devices of its MAC address change so that they can update their
ARP entries.
A device receiving a gratuitous ARP packet can add the information carried in the
packet to its own dynamic ARPmapping table if it finds no corresponding ARPentry for
the ARP packet in the cache.
1.3.2 Configuring Gratuitous ARP
Follow these steps to configure gratuitous ARP:
To do… Use the command… Remarks
Enter system view system-view —
Enable the device to send
gratuitous ARP packets gratuitous-arp-sending
enable
Optional
A device cannot send
gratuitous ARP packets
by default.

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To do… Use the command… Remarks
Enable the gratuitous
ARP packet learning
function
gratuitous-arp-learning
enable Required
Disabled by default.
1.4 Displaying and Maintaining ARP
To do… Use the command… Remarks
Display the ARP entries in
the ARP mapping table
display arp {{ all |
dynamic | static } | vlan
vlan-id | interface
interface-type
interface-number } [ [ |
{ begin | exclude |
include } text ] | count ]
Available in any view
Display the ARP entries
for a specified IP address
display arp ip-address [ |
{ begin | exclude |
include } text ] Available in any view
Display the aging time for
dynamic ARP entries display arp timer aging Available in any view
Display the configuration
information of ARP
source suppression
display arp
source-suppression Available in any view
Clear ARP entries from
the ARP mapping table
reset arp { all | dynamic |
static | interface
interface-type
interface-number }
Available in user view

Operation Manual – ARP
H3C S5500-SI Series Ethernet Switches Chapter 2 Proxy ARP Configuration
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Chapter 2 Proxy ARP Configuration
When configuring proxyARP, go to these sections for information you are interested in:
zProxy ARP Overview
zEnabling Proxy ARP
zDisplaying and Maintaining Proxy ARP
zProxy ARP Configuration Example
2.1 Proxy ARP Overview
For an ARPrequest of a host on a network to be forwarded to an interface that is on the
same network but isolated at Layer 2 or a host on another network, the device
connecting the two physical or virtual networks must be able to respond to the request.
This is achieved by proxyARP.
Proxy ARP can be divided to proxy ARP and local proxy ARP.
Within a network segment, hosts connecting with different VLAN interfaces can
communicate with each other through Layer 3 forwarding by using the proxy ARP
function.
To realize Layer 3 connectivity, you need to enable the local proxy ARP function in the
following two cases.
zThe Layer 2 port isolation function is enabled on the switches attached to the
S5500-SI series Ethernet switches.
zThe isolated-user-vlan function is enabled on the switches attached to the
S5500-SI series Ethernet switches.
2.2 Enabling Proxy ARP
Follow these steps to enable proxy ARP in VLAN interface view/Ethernet interface view
or enable local proxyARP in VLAN interface view:
To do… Use the command… Remarks
Enter system view system-view —
Enter VLAN interface
view interface vlan-interface
vlan-id Required
Enable proxy ARP proxy-arp enable Required
Disabled by default
Enable local proxy ARP local-proxy-arp enable Required
Disabled by default

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2.3 Displaying and Maintaining Proxy ARP
To do… Use the command… Remarks
Display whether proxy
ARP is enabled
display proxy-arp
[ interface vlan-interface
vlan-id ]Available in any view
Display whether local
proxy ARP is enabled
display local-proxy-arp
[ interface vlan-interface
vlan-id ]Available in any view
2.4 Proxy ARP Configuration Example
2.4.1 Proxy ARP Configuration Example
I. Network requirement
PC1 belongs to VLAN1, and PC4 belongs to VLAN2. Configure proxy ARP on the
device to enable the communication between the two.
II. Network diagram
PC3 PC4
Vlan-interface1
192.168.10.99/24
Vlan-interface2
192.168.20.99/24
192.168.10.100/16
0000-0c94-36aa
SubnetA
SubnetB
192.168.20.200/16
0000-0c94-36dd
PC1 PC2
Figure 2-1 Network diagram for proxy ARP
III. Configuration procedure
# Configure Proxy ARP on the device to enable the communication between PC 1 and
PC 4.
<Sysname> system-view

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[Sysname] vlan 1
[Sysname-vlan1] quit
[Sysname] vlan 2
[Sysname-vlan2] quit
[Sysname] interface vlan-interface 1
[Sysname-Vlan-interface1] ip address 192.168.10.99 255.255.255.0
[Sysname-Vlan-interface1] proxy-arp enable
[Sysname-Vlan-interface1] quit
[Sysname] interface vlan-interface 2
[Sysname-Vlan-interface2] ip address 192.168.20.99 255.255.255.0
[Sysname-Vlan-interface2] proxy-arp enable
[Sysname-Vlan-interface2] quit
2.4.2 Local Proxy ARP Configuration Example in Case of Port Isolation
I. Network requirement
zPC1 and PC2 belong to the same VLAN, and are connected to GE1/0/3 and
GE1/0/4 of the switch respectively.
zThe switch is connected to the SwitchA (S5500-28C-SI) via GE1/0/2
zGE1/0/3 and GE1/0/4 isolated at layer 2 can implement layer 3 communication..
II. Network diagram
PC1
GE1/0/3
GE
Switch B
Switch
1/0/1
A
PC1 PC2PC2
GE1/0/4
GE
1/0/1
A
GE
Switch B
Switch
PC1
GE1/0/3
GE
Switch B
Switch
1/0/1
A
PC1 PC2PC2
GE1/0/4
GE1/0/2
1/0/1
A
GE
Switch B
Switch
PC1
GE1/0/3
GE
Switch B
Switch
1/0/1
A
PC1 PC2PC2
GE1/0/4
GE
1/0/1
A
GE
Switch B
Switch
PC1
GE1/0/3
GE
Switch B
Switch
1/0/1
A
PC1 PC2PC2
GE1/0/4
GE1/0/2
1/0/1
A
GE
Switch B
Switch
Figure 2-2 Network diagram for local proxy ARP between isolated ports
III. Configuration procedure
1) Configure the Switch B
# Add GE1/0/2, GE1/0/3 and GE1/0/4 to VLAN 2. PC1 and PC2 are isolated and
unable to exchange Layer 2 packets.

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For detailed configuration information, refer to Port Correlation Configuration.
2) Configure the Switch A (S5500-28C-SI)
# Create VLAN 2, and add GE1/0/1 to VLAN 2.
For detailed configuration information, refer to VLAN Configuration.
# Create vlan-interface 2 on the Switch Aand configure local proxyARP to let PC1 and
PC2 communicate at Layer 3.
<SwitchA> system-view
[SwitchA] interface vlan-interface 2
[SwitchA-Vlan-interface2] local-proxy-arp enable
[SwitchA-Vlan-interface2] quit
2.4.3 Local Proxy ARP Configuration Example in Isolate-user-vlan
I. Network requirement
zSwitch A (an S5500-28C-SI Ethernet switch) connects to Switch B through port
GigabitEthernet1/0/1.
zVLAN 5 on Switch B is an isolate-user-vlan, which contains the uplink port
GigabitEthernet1/0/1 and two secondary VLANs (VLAN 2 and VLAN 3). Port
GigabitEthernet1/0/2 belongs to VLAN2. Port GigabitEthernet1/0/3 belongs to
VLAN3.
zLayer 3 communication is implemented between VLAN 2 and VLAN 3.
II. Network diagram
PC1 PC2
Ethernet1/0/2 Ethernet
Ethernet1/0/1
1/0/3
Switch B
VLAN2 VLAN3
PC1 PC2
GE1/0/2 GE1/0/3
GE1/0/1
GE1/0/1
Switch B
VLAN2 VLAN3
PC1 PC2
Ethernet1/0/2 Ethernet
Ethernet1/0/1
1/0/3
VLAN5
3
Switch B
VLAN2 VLAN
PC1 PC2
GE1/0/2 GE1/0/
GE1/0/1
3
Switch A
Switch B
VLAN2 VLAN3
PC1 PC2
Ethernet1/0/2 Ethernet
Ethernet1/0/1
1/0/3
Switch B
VLAN2 VLAN3
PC1 PC2
GE1/0/2 GE1/0/3
GE1/0/1
GE1/0/1
Switch B
VLAN2 VLAN3
PC1 PC2
Ethernet1/0/2 Ethernet
Ethernet1/0/1
1/0/3
VLAN5
3
Switch B
VLAN2 VLAN
PC1 PC2
GE1/0/2 GE1/0/
GE1/0/1
3
Switch A
Switch B
VLAN2 VLAN3
Figure 2-3 Network diagram for local proxy ARP configuration in isolate-user-vlan
III. Configuration procedure
1) Configure the Switch B

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# Create VLAN 2, VLAN 3, and VLAN 5 on the Switch B. Add GE1/0/2 to VLAN2,
GE1/0/3 to VLAN 3, and GE1/0/1 to VLAN 5. Configure VLAN5 as the isolate-user-vlan,
and VLAN 2 and VLAN 3 as secondary VLANs. Configure the mappings between
isolate-user-vlan and the secondary VLANs.
For detailed configuration information, refer to VLAN Configuration.
2) Configure the Switch A ( S5500-28C-SI )
# Create VLAN5 and add GE1/0/1 to it.
Refer to VLAN Configuration for detailed configuration information
# Create vlan-interface5 on the Router. Configure local proxy ARP to implement
communication between VLAN 2 and VLAN 3.
<SwitchA> system-view
[SwitchA] interface vlan-interface 5
[SwitchA-Vlan-interface5] local-proxy-arp enable
[SwitchA-Vlan-interface5] quit