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--- advanced-firewall [2023/05/28 05:05] – [Multicast] -clarity of IGMP Snooping and Force IGMPv2 details hogwild
+++ advanced-firewall [2023/05/28 05:39] (current) – [Multicast] -condense, list/explain additional features of new IGMPv2 messages hogwild
@@ Line 73: / Line 73: @@
 **Udpxy port**- This specifies the port on which you can recive Udpxy information from your router.\\  \\   \\  {{:pasted:20220118-190844.png}}\\  \\
-**Efficient Multicast Forwarding (IGMP Snooping) -** IGMP snooping makes the router's switch facilitate discovery of Multicast IGMP clients. This will help to send multicast traffic only towards ports with at least one multicast subscriber.
+**Efficient Multicast Forwarding (IGMP Snooping) -** IGMP snooping makes the router's switch facilitate discovery of Multicast IGMP clients. This will help to send multicast traffic only towards ports with at least one multicast subscriber, reducing overall multicast traffic.
-However, caution is advised. Often, UPnP or DLNA is the only significant multicast application in use on a home network. Thus, multicast configuration issues or other deficiencies can appear as UPnP issues, but are actually underlying network issues.
+However, caution is advised. IGMP Snooping can interfere with proper functioning of UPnP or DLNA. This can make Multicast configuration errors or deficiencies appear as UPnP issues. Enabling IGMP snooping on a router's/switch will interfere with UPnP/DLNA device discovery.  Specifically, it can interfere with SSDP protocol transmissions. If IGMP snooping is incorrectly or incompletely configured (say, without an active querier or IGMP proxy), this make UPnP appear unreliable.
-Enabling IGMP snooping on a wireless router's/switch will interfere with UPnP/DLNA device discovery. Specifically, the SSDP protocol transmissions. If IGMP snooping is incorrectly or incompletely configured (say, without an active querier or IGMP proxy), this make UPnP appear unreliable.
+A common symptom of this is a network host (say, a Smart TV) which appears after it's powered on, but then "disappears" from the network after a few minutes. To be more precise, often this period is 30 minutes. This is because the default setting for when IGMP group membership will expire. Please be aware of the wireless multicast forwarding setting in the the //Advanced///[[advanced-wireless|Wireless]] menu.
-A common symptom of this is a network host (say, a Smart TV) which appears after it's powered on, but then "disappears" from the network after a few minutes. To be more precise, often this period is 30 minutes. This is because the defaut setting for when IGMP group membership will expire. Please be aware of the wireless multicast forwarding setting in the the //Advanced///[[advanced-wireless|Wireless]] menu.
+**Force IGMPv2** - IGMPv2 enhances IGMP with additional messages/behavior to optimize end-to-end client-server communication. Perhaps the most important of these additional messages is the "Leave Group" message. When a host no longer wants to listen to a multicast group address, it will report to the router that it has stopped listening. In v1, the host simply stopped listening, without informing the router.
-**Force IGMPv2** - IGMPv2 enhances IGMP with additional messages/behavior to optimize end-to-end client-server communication. Perhaps the most important of these additional messages is the "Group Leave" message. This message did not exist in previous IGMP versions.\\   \\
+Other features of IGMPv2 include:
+Group specific membership query. The router can now send a membership query for a specific group address. When the router receives a leave group message, it will use this query to check if there are still any hosts interested in receiving the multicast traffic.
+MRT (Maximum Response Time) field. This new field in query messages specifies how much time hosts have to respond to the query.
+Querier election process. When two routers are connected to the same subnet, only one of them should send query messages. Having an "election" process ensures only one router, the router with the lowest IP address, becomes the active querier.\\   \\

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