如何於飯店IPTV架構下在 Omada 交換器上設定 IGMP Snooping

適用於Omada L2+和 L3交換器，Omada SDN控制器 V5及以上。

 

本文將介紹如何在飯店 IPTV場景中，透過 Omada 交換器分別於獨立模式和控制器模式兩種模式下設定 IGMP  Snooping。

 

注意：本文提供的所有 CLI指令僅實現基本功能，並僅以 Gigabit Ethernet 埠為例，欲了解更詳細的設定和參數，請參閱 CLI手冊。

 

1、典型架構

飯店的IPTV場景，典型架構如下：

 

與小型辦公室 / 家庭辦公室 (SOHO) 場景不同，飯店的 IPTV 伺服器或 IPTV multicast 來源通常會包含在飯店區域網路 (LAN) 中，因此multicast串流不會來自WAN端。IPTV 來源通常連接到核心交換器或接在核心交換器下的存取交換器，接著multicast串流才能傳送到 LAN 中的所有IPTV設備。存取交換器連接至核心交換器，並直接或透過房間內AP連接到飯店的電視。

 

2、IGMP系統如何運作

IGMP系統由以下部分組成：Multicast來源、IGMP Querier、IGMP Snooping、IGMP Receiver，請查看下圖：

 

對於我們的產品而言，運作 IGMP Snooping功能的設備是交換器，另外我們的交換器能設定為IGMP Snooping Querier，取代圖中的querier設備。

在IGMP Snooping v2中，有三種 IGMP 封包類型，IGMP Query、IGMP  Report以及IGMP Leave。對Multicast Source而言，若其不支援query功能，它會直接廣播所有的串流，這會造成網路資源的浪費，啟用IGMP Snooping可以解決問題。Querier將會發送IGMP Query，包含general query以及specific query，這裡通常會是發出general query，它會詢問網路上是否有任何設備請求multicast串流。接著交換器會轉發這個IGMP Query，最後到達IGMP Receiver(如：IPTV)。如果有人想看特定頻道，IPTV 會發送IGMP Report，其中包含頻道資訊，用於請求該串流，同時也會加入這個 multicast群組。當使用者切換到另一個頻道 （這表示 IPTV 不再需要這個串流），它會發送 IGMP Leave訊息已離開multicast群組。

對於所有運行IGMP Snooping功能的設備，為了協助建立multicast群組，會用到兩種埠角色：路由埠和成員埠。對交換器而言，接收IGMP Query封包的埠將會變成路由埠，而接收IGMP Report/leave封包的埠則會變為成員埠。您也可以將路由埠視為最靠近querier的埠，成員埠則是最靠近receiver。經過前提的query過程後，運作IGMP Snooping的交換器將建立multicast群組，包含串流的multicast IP、串流所在的VLAN，以及參與此群組的埠(路由埠和成員埠)。如先前所述multicast來源會直接在網路上廣播串流，在multicast群組建立後，交換器只會把對應的multicast串流轉發至路由埠及成員埠，而IGMP Report/Leave封包僅會自成員埠轉發到路由埠。

The basic working process of IGMP v2 is like this, and IGMP v3 has carried out some features to make the whole process more efficient, but the basic process and theory is the same as v2.

 

3. Overall Configuring Principles

Here we will introduce the overall configuring principles for IGMP Snooping, taking the previous topology as an example. These are some recommendations we made when configuring IGMP Snooping, which will help avoid misfunction and improve device efficiency, bringing a better user experience.

 

3.1 Disable IGMP featuers for router.

In hotel IPTV scenario, as the IPTV source is included in the LAN, so the multicast stream will not be entering from WAN side, and the router will actually not participate in the whole IGMP process. If you enable the IGMP feature on the router, then it will be recognized as a querier, so the switch port connecting to it will become a router port, and after that, a copy of all the multicast streams will be forwarded to the router, causing unnecessary load to the router, which may lead to high CPU and memory occupancy on router, affecting the normal function of router. That’s the reason why it’s recommended to disable the IGMP Query or IGMP Proxy feature on the router, no matter it’s TP-Link router or from other vendors.

 

3.2 Enable drop packets from unknown multicast groups.

When configuring IGMP Snooping, you can choose to forward or discard the packets of unknown groups. Here, we recommend you choose to discard all the packets from unknown groups, the reason is that for unknown groups, there isn’t a table recording the member ports, so actually the switch doesn’t know where these packets should be forwarded, and if you choose to forward them, they will be broadcasted, causing a waste of network resource, so the best choice is to discard them.

 

3.3 IGMP Snooping Querier should be closest to source.

In hotel IPTV scenario, as the source needs report from end devices to determine which streams to be multicasted, an IGMP Snooping Querier is needed. There should be only one querier in the network and should be configured only on the switch closest to the IPTV source. Check the following figure for more intuitive explanation:

 

Here you can see, the Querier will send IGMP Query to others, which means it won’t receive any IGMP Query from others, so there isn’t a router port on the Querier, as we know that the switch with IGMP Snooping enabled will forward the IGMP Report to the router port, so in this scenario, this Querier will not forward the IGMP Report to anyone. The other switch won’t receive any IGMP Report, so no multicast group will be created, though the multicast source is keep sending the streams, all of them will be regarded as streams of unknown groups and got dropped because there isn’t any multicast group created on this switch. Set the switch cloeset to the multicast source as Querier will avoid this problem, the IGMP Snooping will be able to take affect through the whole network, save network resource while ensuring the multicast function normally.

 

3.4 Fast leave and report suppression should be closest to end device.

Fast leave will remove the port from IGMP group immediately when the switch receives the IGMP leave from end device, so the IPTV could switch to another channel faster, providing the users with a smooth experience, if not enabled, another specific query will be sent after receiving IGMP leave in order to determine if there are more IPTVs asking for this stream.

Report suppression will collect IGMP report for a same stream coming from different member ports and finally send out only one IGMP report through the router port, which will reduce the load for uplink, it’s recommended to enable report suppression in large multicasting networks, for example over three to four hundreds of IPTVs installed.

If you need to enable these two features, do remember to configure them on the access switch or the switch directly connecting the IPTVs. Check the figure below:

 

For fast leave, you need to ensure that there is only one IPTV connected to this port, so terminating the stream as soon as IGMP leave received will not affect other IPTVs watching the same channel. It’s not recommended to enable fast leave in the scenario shown in the figure when more than one IPTV is connected on one member port, enabling fast leave on this port will interrupt the stream for another TV still watching, it’s the same if you enable it on any higher level uplink switches, so remember to enable fast leave only on the access switch, and the ports connecting to only one IPTV.

For report suppression, enabling it on the access switch will save the most network resource for the whole network, the total number of IGMP Report packets will be lowered from the very beginning and save the bandwidth of uplinks, suppressing report on core switch but not access switch will be meaningless.

 

3.5 In case you have multiple IPTV sources in LAN.

Sometimes there are more than one IPTV sources in the network, it’s recommended you connect them to the same switch, and set this switch as IGMP Snooping Querier, this switch will also send general query to all the IPTV sources.

If your IPTV sources responde to the query, the switch will also establish IGMP groups for these IPTV sources, recording which port each stream is coming from, so the stream will not be forwarded to another IPTV source, causing heavy load or misfuntion on the source.

If your IPTV source do not respond to the IGMP query, you have two choices:

The first one is to configure configure port isolation and block the communication between the ports connected to each IPTV source.

Below are the configuration methods in standalone mode and controller mode.

• Configure port isolation in standalone mode:

Go to L2 FEATURES – Switching – Port – Port Isolation, here you will see a table, showing the ports and their forwarding list, the port will only be able to communicate with the ports included in the forwarding port list.

 

Click Edit on the upperright of the table to edit the forwarding list, for example, I want to cut the communication between port 1 and 2, just select port 1 and unselect port 2 for its forwarding port list, click Apply.

• Configure port isolation in controller mode:

In controller mode, go to Devices, click on the device connected with multiple IPTV Sources, in the device’s private configuration page, go to Ports, click the edit button of the ports connected with the IPTV Sources, tick Profile Overrides, then tick Port Isolation.

In controller mode, the communication between the ports with port isolation enabled will be cut, but kept the communication normal between the ports enabled and disabled port isolation.

Please note that when configuring profile override with this method, the profile override is enabled, which will override the configurations you made in the port profile, remember to make the necessary changes here.

 

The second one is to configure static IGMP group on the switch, manually create the groups and assign member ports to ensure the stream will not be forwarded from an IPTV source to another.

Below are the configuration methods in standalone mode and controller mode:

 

• Configure static multicast group in standalone mode:

Go to L2 FEATURES – Multicast – IGMP Snooping – Static Group Config, here is where you can configure the static multicast group in standalone mode, you will be able to manually bind the multicast IP, VLAN ID and the designated member ports.

 

When entering the static group config page, you will see the static multicast group table, click Add on the upper right of the table to start to configure a new static group, just input the corresponding multicast IP, the VLAN ID this multicast stream is running in, and select the member ports you want to add, in this scenario, just select the port connected to one of your IPTV Source and another port connected to the main network, for example, I have one of the IPTV Source connected to port 1 and the port 3 connected to core switch, so I just add port 1 and 3 into the static group. After configured, the multicast stream coming out of one IPTV Source will only be forwarded to the main network but not to any other IPTV Source.

 

• Configute static multicast group in controller mode:

In controller mode, port isoaltion needs to be configured through CLI template.

Go to Settings – CLI Configuration – Device CLI, click Create New Device CLI Profile, enter a name, description for it and then enter the CLI commands.

For example, one of my IPTV Source is connected to port 1, and port 3 is connected to the core switch, this IPTV Source is sending the stream with IP 235.0.0.1, running in VLAN 10, here is the command:

ip igmp snooping vlan-config 10 static 235.0.0.1 interface gigabitEthernet 1/0/1,1/0/3

As you have multiple multicast groups to be configured, you can enter all the commands here group by group. After finished entering the commands, click Next, and choose the device you want to apply the CLI.

Then click Confirm, then Save and you will see this CLI Template you have just created, click Apply to apply it on the chosen devices, you can also check if it has successfully applied by clicking View CLI Details on the upper-right corner.

 

4. Configuration under Standalone Mode

After entering the web GUI, you will find the IGMP related configurations in L2 FEATURES – Multicast – IGMP Snooping. You will find it divided into four parts: Global Config, Port Config, Static Group Config, IGMP Authentication. We will introduce the configuration for these parts.

 

4.1 Global Config

This is the basic configuration page of IGMP Snooping, for the switches participating IGMP, you need to enable IGMP Snooping.

• IGMP Snooping: Ticking enable will enable it globally on the device.
• IGMP Version: The IGMP protocol is backward compatible, so you can simply choose v3, it will work well with other devices which support v1 or v2 only.
• Unknown Multicast Groups: It decides how will the switch process the stream with no IGMP group exsited, which means currently no one wants to watch it or it’s a stream sending to an unknown group. It’s recommended to set it as Discard in order to save network resource.
• Header Validation: Enabling it will check a few sums in the header, if the sums don’t match IGMP protocol, this packet will be dropped. We suggest not to enable it as some IPTV vendors may not closely follow the corresponding protocol, causing the packets created not able to pass the validation and got dropped, leading to misfunction of the whole system.

After finished configuring these four options, don’t forget to click Apply to apply it to the device.

For the IGMP VLAN Config, it will display all the VLANs created on the device, usually all the IPTV streams run in a dedicated VLAN, so please create a VLAN Interface for the IPTV stream first, then you will find this VLAN in the IGMP VLAN Config. You can click the edit button on the right of this VLAN and enter the VLAN config page.

• IGMP Snooping Status: Tick Enable to enable IGMP Snooping for VLAN.
• Fast Leave, Report Suppression: Decide whether to enable fast leave and report suppression on this device, please follow the principle from previous chapter.
• Member Port Aging Time, Router Port Aging Time, Leave time: Keep default or configure as you want.
• IGMP Snooping Querier: Please check the previous chapter about where you should enable the switch as an IGMP Snooping Querier. Tick Enable to set this switch as IGMP Snooping Querier and configure parameters including Query Interval, Maximum Response Time, Last Member Query Interval and Last Member Query Count, you can just keep it as default or set it manually as you like. For the General Query Source IP, it’s the IP address used to send the IGMP Query, ususally you should set it as the IP address of this switch, so it will be more convenient for you to check the packets sent from this querier.
• Static Router Ports, Forbidden Router Ports: No need to configure.

After finished configuring the IGMP VLAN configuration, click Save.

 

4.2 Port Config

After configuring IGMP on this device globally and per VLAN, you also need to perform the port config, you can config it per port or LAG group. You need to config the IGMP Snooping and fast leave status for each port or LAG group.

Here you will see that for IGMP Snooping and Fast Leave, you can also choose to enable or disable them by port, by default, the IGMP Snooping is enabled on all ports, and Fast Leave is disabled on all ports. Explanation as below:

• IGMP Snooping: You can choose to enable or disable it globally, per VLAN and per port. To enable it on port A included in VLAN B, you must enable IGMP Snooping globally, in VLAN B and on port A, IGMP Snooping will take affect on a port only when the IGMP Snooping is enabled on all these three layers.
• Fast Leave: You can choose to enable or disable it per VLAN and per port and it will take affect with only one layer enabled. For example, port A and B is included in VLAN C. If you only enable it in VLAN C, even if you don’t enable it on port A and B, it will also take affect on them. If you enabled it on port A but not on port B and VLAN C, it will also take affect on port A.

 

4.3 Static Group Config

In Static Group Config, you can click Add to configure and add static IGMP groups. To add a group, you need to configure the multicast IP address for this group and also the VLAN running this multicast group. Then choose the member ports you want to manually add into this static multicast group. After added, all the static multicast group including its VLAN ID and multicast IP, member ports will be displayed in the table.

 

4.4 IGMP Authentication

Keep it by default.

 

5. Configuration under Controller Mode

When using the devices in controller mode, the first step is also creating a VLAN for IGMP, go to Settings – Wired Networks – LAN – Networks, click Create New LAN, configure it as VLAN, applies on switches only, and then tick to enable the IGMP Snooping, if you need IPv6 version, tick to enable MLD Snooping too. Then click save.

 

Here, the GUI configuration has finished, you will need to configure the rest parameters through CLI Template.

Go to Settings – CLI Configuration – Device CLI, click Create New Device CLI Profile, enter a name, description for it and then enter the CLI commands.

Please note that you can also choose to configure this device under standalone mode, and export its config file, then copy it here.

Below is the CLI commands on configuring IGMP Snooping based on the topology shown in chapter 1 and the principles in chapter 3 (with IPTV VLAN ID=100):

 

• Core switch and Aggregation switch:

ip igmp snooping drop-unknown

 

• Access switch to IPTV:

ip igmp snooping drop-unknown

ip igmp snooping vlan-config 100 report-suppression

ip igmp snooping vlan-config 100 immediate-leave (If all the ports on this switch connect to only one IPTV, if not, don’t use this command and use the below command to enable it by port)

interface gigabitEthernet 1/0/1

ip igmp snooping immediate-leave

#

 

• Access switch to IPTV Source:

ip igmp snooping drop-unknown

ip igmp snooping vlan-config 100 querier

 

For more CLI commands used to configure more parameters, please check the CLI Guide on product’s support page.

After finishing entering the commands, click Next, and choose the device you want to apply the CLI.

 

 

Then click Confirm, then Save and you will see this CLI Template you have just created, click Apply to apply it on the chosen devices, you can also check if it has successfully applied by clicking View CLI Details on the upper-right corner.

For all the parameters you can configure, please check chapter 3, the configuration under standalone mode. Also, remember to configure different parameters and features for switches in different positions of your topology following the priciple introduced in chapter 2.

 

Here we have finished introducing how to configure IGMP Snooping for typical hotel IPTV scenario on Omada L2+ and L3 switches under standalone mode or through Omada SDN Controller.