H3C S9500 Series Manuel utilisateur

Operation Manual – URPF

H3C S9500 Series Routing Switches Table of Contents

Table of Contents

Chapter 1 URPF Configuration ....................................................................................................1-1

1.1 URPF Overview.................................................................................................................1-1

1.2 Configuring URPF..............................................................................................................1-2

1.3 URPF Configuration Examples..........................................................................................1-3

1.3.1 Example I ................................................................................................................1-3

1.3.2 Example II ...............................................................................................................1-4

Operation Manual – URPF

H3C S9500 Series Routing Switches Chapter 1 URPF Configuration

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Chapter 1 URPF Configuration

When configuring URPF, go to these sections for information you are interested in:

zURPF Overview

zConfiguring URPF

zURPF Configuration Examples

Note:

The service processor boards mentioned in the chapter refer to LSB1NAMB0 boards.

1.1 URPF Overview

Unicast reverse path forwarding (URPF) serves as a safeguard against source address

spoofing attacks.

In general, a routing switch routes packets according to their destination. If finding the

best routes, routing switches transfer the packets, otherwise, discard the packets.

After URPF is enabled, switches obtain the source addresses and incoming interfaces

of packets. Then switches search routes to the destination addresses (that is the

source addresses) in routing tables. If the outgoing interfaces are found inconsistent

with the incoming interfaces, switches assume the source addresses are forged, and

discard the packets.

URPF can prevent malicious attackers from modifying source addresses. The following

figure shows the common attack mode.

1.1.1.1 2.1.1.1

SwitchA SwitchB SwitchC

Source address

2.1.1.1

Figure 1-1 Source address spoofing attacks

Forge packets with source address 2.1.1.1 onSwitch A, and send a request to Switch B

server. Then Switch B responds to the request and sends packets to the address

2.1.1.1 if Switch B does not perform URPF check. The illegal packets can attack both

Switch B and Switch C.

Operation Manual – URPF

H3C S9500 Series Routing Switches Chapter 1 URPF Configuration

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1.2 Configuring URPF

The following section describes the URPF configuration tasks:

zConfigure packet redirection

zEnable URPF on ports

zDisplay port configuration information

zClear URPF statistical counters to zero

Use the urpf enable command to enable URPF for a certain VLAN port and specify the

service processor board where the port locates. Configure to redirect packets in port

view to the service processor board to make data flow reach the service processor

board.

Caution:

Because URPF and virtual private LAN service (VPLS) are mutually exclusive, you

cannot simultaneously enable URPF and VPLS in the same VLAN interface view.

After enabling URPF on a current VLAN port, you can use the display urpf command

to view the configuration. If the enabled and specified NAM server processor card is

inserted in the slot, you can also view the statistical data related to URPF on the port.

When a VLAN port with URPF enabled runs for a long time, more statistical data enter

the counter. Therefore you need to clear statistical data related to URPF on the port. To

clear recording statistics of received and rejected data packets on the port, execute the

reset urpf statistic command. As a result, the URPF statistical counter is cleared to

zero.

Follow these steps to enable URPF on a port and specify the corresponding

LSB1NATB boards for handling:

To do… Use the command… Remarks

Enter system view system-view —

Enter Ethernet port view interface ethernetX/1/X —

Configure packet

redirection

traffic-redirect inbound

ip-group {acl-number |

acl-name } [ rule rule

link-group { acl-number |

acl-name } [ rule rule

[system-index index ]]|

link-group {acl-number |

acl-name } rule rule ]slot

slotnum designated-vlan

vlanidex

Required.

The service processor

board does not support

multicast currently. You

can prohibit multicast

packets from being

redirected to the service

processor board through

ACL

Operation Manual – URPF

H3C S9500 Series Routing Switches Chapter 1 URPF Configuration

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To do… Use the command… Remarks

Quit to system view quit —

Enter VLAN interface

view interface vlan-interface

vlan-id —

Enable URPF on a port urpf enable to slot slotid

Required.

Enable URPF in VLAN

interface view. Specify

corresponding slot of a

service processor board

to perform URPF check.

By default, URPF is

disabled.

Display configuration

information display urpf —

Clear URPF statistical

counters to zero reset urpf statistic —

Note:

zIn access control lists, redirection configuration is only valid for permit action of the

rule.

zWhen you are configuring the traffic-redirect command to redirect packets, you

must prohibit multicast packets from being redirected to the service processor board

through ACL.

1.3 URPF Configuration Examples

1.3.1 Example I

I. Network requirements

What differs from routers is that, for switches, you can enable URPF on VLAN

interfaces, and configure only packet redirection on every port. Packets to be checked

are sent to the service processor board and then are forwarded or discarded after the

system performs URPF procedure on them.

II. Network diagram

ISP

G6/1/2

SwitchA SwitchB

VLAN 1000 E3/1/30

Figure 1-2 Network diagram for URPF configuration

Operation Manual – URPF

H3C S9500 Series Routing Switches Chapter 1 URPF Configuration

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III. Configuration procedure

As for Switch B, assume that the service processor board is installed in slot 5, and

normal access boards are installed in slot 3 and 3.

# Configure VLAN 1000.

[H3C] vlan 1000

[H3C-vlan1000] port Ethernet 3/1/30

[H3C-vlan1000] port GigabitEthernet6/1/2

[H3C] interface vlan-interface 1000

[H3C-Vlan-interface1000] ip address 10.10.10.1 24

# Configure flow templates. Specify the flow template of the two access boards installed

in slot 3 and slot 6 to extract the destination MAC addresses and Ethernet protocol

fields of the packets.

[H3C] flow-template user-defined slot 3 dmac 00-00-00 ethernet-protocol

[H3C] flow-template user-defined slot 6 dmac 00-00-00 ethernet-protocol

# Create an ACL of Layer 2.

[H3C]acl number 4000

# Define a rule that permits IP packets whose destination MAC addresses are that of

the interface (01-02-03).

[H3C-acl-link-4000] rule 0 permit ip egress 01-02-03 00-00-00

# Configure packet redirecting on the corresponding Ethernet port.

[H3C] interface ethernet 3/1/30

[H3C-Ethernet3/1/30] flow-template user-defined

[H3C-Ethernet3/1/30] traffic-redirect inbound link-group 4000 slot 5 vlan 1000

[H3C-Ethernet3/1/30] quit

[H3C] interface GigabitEthernet 6/1/2

[H3C-GigabitEthernet6/1/2] flow-template user-defined

[H3C-GigabitEthernet6/1/2] traffic-redirect inbound link-group 4000 slot 5

designated-vlan 1000

[H3C-GigabitEthernet6/1/2] quit

# Enable URPF in VLAN 1000.

[H3C] interface vlan-interface 1000

[H3C-Vlan-Interface1000] urpf enable to slot 5

1.3.2 Example II

I. Network requirements

NAM board is placed in slot 5.

Operation Manual – URPF

H3C S9500 Series Routing Switches Chapter 1 URPF Configuration

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Create two virtual interfaces, VLAN interface 1000 and VLAN interface 1001; enable

URPF on them and use the NAT service processor board in slot 5 to perform URPF

check.

Port Ethernet 6/1/1 is a trunk port, permitting packets of VLAN 1000 and VLAN 1001.

It is required that port Ethernet 6/1/1 performs URPF check on packets of VLAN 1000

and VLAN 1001.

II. Network diagram

ISP

SwitchA SwitchB

VLAN 1000 Ethernet6/1/1

VLAN1001 Trunk口

Figure 1-3 Network diagram for URPF

III. Configuration procedure

# Configure VLAN information.

[H3C] vlan 1000

[H3C-vlan1000] vlan 1001

[H3C-vlan1001] quit

[H3C] interface ethernet 6/1/1

[H3C-Ethernet6/1/1]quit

[H3C] vlan 1001

[H3C-vlan1001] quit

[H3C] interface vlan-interface 1000

[H3C-Vlan-interface1000] ip address 10.10.10.1 24

[H3C-Vlan-interface1000] interface vlan-interface 1001

[H3C-Vlan-interface1001] ip address 11.11.11.1 24

# Enable URPF on the VLAN interfaces.

[H3C-Vlan-interface1000] urpf enable to slot 5

[H3C-Vlan-interface1000] interface vlan 1001

[H3C-Vlan-interface1001]urpf enable to slot 5

# Create a layer 2 ACL rule

<H3C> system-view

[H3C] acl number 4000

# Permit the IP packets going into VLAN 1000 and the DMAC must be the interface

MAC000f-e239-a9b8.

[H3C-acl-link-4000] rule 0 permit ip ingress 1000 egress 000f-e239-a9b8

0000-0000-0000

# Permit the IP packets going into VLAN 1001.

Operation Manual – URPF

H3C S9500 Series Routing Switches Chapter 1 URPF Configuration

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[H3C-acl-link-4000] rule 1 permit ip ingress 1001 egress 000f-e239-a9b8

0000-0000-0000

# Configure a user-defined flow template.

[H3C] flow-template user-defined slot 6 vlanid ethernet-protocol dmac 00-00-00

# Apply the flow template on port Ethernet 6/1/1 and configure traffic redirection.

[H3C-Ethernet6/1/1] flow-template user-defined

[H3C-Ethernet6/2/1] traffic-redirect inbound link-group 4000 rule 0 slot 5

designated-vlan 1000

[H3C-Ethernet6/1/1] traffic-redirect inbound link-group 4000 rule 1 slot 5

designated-vlan 1001

Note that the ingress VLAN IDs configured in the rules added to ACL4000 must be the

same as the ones specified when configuring traffic redirection. The trunk port checks

URPF by VLAN.

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