Ip igmp snooping router-alert-option-check, Ip igmp snooping router-port-expire-time – Brocade Communications Systems Brocate Ethernet Access Switch 6910 User Manual

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Brocade 6910 Ethernet Access Switch Configuration Guide

451

53-1002581-01

IGMP Snooping

23

Command Usage

IGMP snooping querier is not supported for IGMPv3 snooping (see

ip igmp snooping version

).

If enabled, the switch will serve as querier if elected. The querier is responsible for asking
hosts if they want to receive multicast traffic.

Example

Console(config)#ip igmp snooping querier

Console(config)#

ip igmp snooping router-alert-option-check

This command discards any IGMPv2/v3 packets that do not include the Router Alert option. Use
the no form to ignore the Router Alert Option when receiving IGMP messages.

Syntax

[no] ip igmp snooping router-alert-option-check

Default Setting

Disabled

Command Mode

Global Configuration

Command Usage

As described in Section 9.1 of RFC 3376 for IGMP Version 3, the Router Alert Option can be used to
protect against DOS attacks. One common method of attack is launched by an intruder who takes
over the role of querier, and starts overloading multicast hosts by sending a large number of
group-and-source-specific queries, each with a large source list and the Maximum Response Time
set to a large value.

To protect against this kind of attack, (1) routers should not forward queries. This is easier to
accomplish if the query carries the Router Alert option. (2) Also, when the switch is acting in the
role of a multicast host (such as when using proxy routing), it should ignore version 2 or 3 queries
that do not contain the Router Alert option.

Example

Console(config)#ip igmp snooping router-alert-option-check

Console(config)#

ip igmp snooping router-port-expire-time

This command configures the querier time out. Use the no form to restore the default.

Syntax

ip igmp snooping router-port-expire-time seconds

no ip igmp snooping router-port-expire-time

seconds - The time the switch waits after the previous querier stops before it considers it
to have expired. (Range: 1-65535; Recommended Range: 300-500)

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