Layer 2 Multicast

Attack Behavior

A malicious user accesses a switch using changed multicast addresses over invalid multicast channels. As a result, a large number of invalid entries are created on the switch and use system resources, and normal users cannot use services.
A malicious user accesses a switch over many multicast channels to occupy system resources. As a result, multicast traffic consumes a lot of interface bandwidth.
An attack is launched using query packets, and the multicast switch port on a switch receives traffic from all multicast groups. As a result, a large amount of traffic is sent through this port, which consumes a lot of bandwidth.

Security Policy

To defend against the preceding attacks, configure the following security policies on a switch:

Run the group-policy command to configure a group policy to specify the multicast groups (multicast source groups) that can access a VLAN or interface to prevent malicious users from using invalid multicast channels to access the switch.
Use Layer 2 multicast Call Admission Control (CAC) to restrict the number or bandwidth of multicast groups to specify the maximum number of multicast groups that can access a VLAN or interface. You can configure the switch to discard unknown multicast packets to prevent the access of malicious users using a large number of multicast channels.
Disable the switch port learning function of switch ports.

Configuration Method

Configure a multicast group policy.

Configure a multicast group policy in the VLAN or Virtual Switching Instance (VSI) view based on service deployment conditions (Internet Protocol Television (IPTV) multicast group address range recommended).
Allow hosts in VLAN 2 to join multicast group 225.1.1.123.
```
<HUAWEI> system-view
[HUAWEI] acl number 2000
[HUAWEI-acl-basic-2000] rule permit source 225.0.0.0 0.0.0.255
[HUAWEI-acl-basic-2000] quit
[HUAWEI] igmp-snooping enable
[HUAWEI] vlan 2
[HUAWEI-vlan2] igmp-snooping enable
[HUAWEI-vlan2] igmp-snooping group-policy 2000
```
Configure a CAC limit.

Configure a CAC limit in the VLAN, VSI, or interface view.

Set the maximum number of multicast groups in VSI company1 to 1000.
```
<HUAWEI> system-view
[HUAWEI] mpls l2vpn
[HUAWEI] vsi company1
[HUAWEI-vsi-company1] l2-multicast limit max-entry 1000
```

Disable the switch port learning function.

Disable the switch port learning function in the VLAN, VSI, or interface view.

Disable the switch port learning function of GE0/0/1 in VLAN 10.

<HUAWEI> system-view
[HUAWEI] igmp-snooping enable
[HUAWEI] vlan 10
[HUAWEI-vlan10] igmp-snooping enable
[HUAWEI-vlan10] quit
[HUAWEI] interface gigabitethernet 1/0/1
[HUAWEI-GigabitEthernet1/0/1] undo igmp-snooping router-learning vlan 10