
The AR1200-S supports the following types of URPF check modes:
l
Strict check: Packets can pass the check only when the FIB table of the AR1200-S has a
corresponding routing entry with the destination address being the source address of the
packet and the inbound interface of the packets matches the outbound interface in the
routing entry. Unmatched packets are discarded.
l
Loose check: A packet can pass the check as long as the FIB table of the AR1200-S has a
routing entry with the destination address being the source address of the packet.
8.3 Configuring URPF
This section describes how to configure URPF.
Applicable Environment
Users on an enterprise network are often attacked by unauthorized users on other network
segments when they use applications demanding IP address-based authentication. An attacker
sends bogus packets with the IP address of an authorized user to a server to access the server.
As a result, the authorized user cannot access the server or the authorized user information is
intercepted. To prevent such an attack, configure URPF on the AR1200-S.
, Network 1 and Network 2 are connected to GE1/0/0 and GE2/0/0 of
RouterA. URPF strict check is configured on GE1/0/0 and GE2/0/0.
PC A on Network 1 sends a bogus packet with the source IP address 2.2.2.2 to the server on
Network 3. After RouterA receives this packet, it checks the inbound interface. Packets with the
source address 2.2.2.2 must reach Network 3 through GE2/0/0 but not GE1/0/0. Therefore,
RouterA considers the packet as a bogus packet and discards it. This protects PC B on Network
2 against IP address spoofing attacks initiated from PC A.
Packets sent from Network 2 to the server pass the URPF check and are forward normally.
Packets sent from VLAN 10 to the server pass the URPF check and are forward normally.
Figure 8-2
URPF application
PC B
RouterA
Eth1/0/0
2.2.2.2/24
3.3.3.3/24
Server
1.1.1.1/24
URPF
enabled
RouterB
Network1
Network2
Network3
Eth2/0/0
PC A
Huawei AR1200-S Series Enterprise Routers
Configuration Guide - Security
8 IP Address Anti-spoofing Configuration
Issue 02 (2012-03-30)
Huawei Proprietary and Confidential
Copyright © Huawei Technologies Co., Ltd.
164