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21 votes
Accepted

What are the benefits and cons of IGMP snooping?

IGMP Snooping is a feature for switches to learn what multicast groups are needed on which ports. Routers not handling multicast routing don't care. That said, without an mrouter in the network, you ...
  • 29.8k
9 votes

OSPF and its use of Multicast

The benefit of multicast is that hosts not subscribing to the multicast group ignore frames they receive that are sent to the multicast group. With broadcast, they cannot ignore the frames. The OSPF ...
  • 94.6k
7 votes
Accepted

Multicast between VLANs

VLANs logically break a switch into multiple, unconnected switches. There is no traffic between VLANs (layer-2), except through a router (layer-3). By default, routers do not route multicast packets. ...
  • 94.6k
5 votes
Accepted

KEMP load balancers using UCARP (VRRP) - multicast MAC address not being picked up

I was able to resolve the issue. On the Kemp (with HA pair) you have the option of using a "Virtual MAC Address". If this box isn't checked, then the MAC of a load balancer VIP is that of the physical ...
5 votes

Multicast between VLANs

There is no inter-VLAN communication without a router. Multicasts are not usually routed - unless your router is specifically configured to do so.
  • 72.9k
4 votes

Multicast routing on Huawei Quidway 5300 Switches

It’s been a while since I used VLC, but when you set up the server end, check to make sure that the TTL of your stream isn’t set to 1 (which used to be the default), otherwise the stream will never ...
4 votes
Accepted

IGMP snooping across VLANs

Switches with multiple VLANs look like multiple switches, and they maintain separate tables for each VLAN. For example, a switch with two VLANs will have two MAC address tables, one for each VLAN. ...
  • 94.6k
4 votes

How do you disable IGMP-snooping on virtual nic macvtap

This is actually a known issue and there are a couple of ways to fix it. The best one is actually to edit the XML definition for the libvirt network and add trustGuestRxFilters=yes to the ...
  • 6,046
4 votes

Multicast Distribution with PIM

Remember that "ip igmp join-group" will cause all multicast packets for this group to be forwarded also to the CPU. Probably this is not what you want. Instead talk to your provider and tell them to ...
  • 628
4 votes
Accepted

OSPF and its use of Multicast

In terms of what happens to OSPF hello/discovery multicast packets, you're right. The switches send them to everyone on the subnet/VLAN/broadcast domain, as IGMP snooping isn't happening for 224.0.0.0/...
3 votes
Accepted

Multicast Distribution with PIM

I have resolved the issue. As you told me , pim must be enabled, sparse-mode in the interface vlan, the rp-address for the multicast group but one command was missing. ip route-cache distributed ...
  • 501
3 votes

Multicast Distribution with PIM

The static igmp join on your vlan 10 should be enough to get the mcast data into the switch. So since your switch now knows how to get to the mcast data you can cheat and make the RP your switch. ...
3 votes

IGMP and Multicast

How IGMP specifically works depends on the IGMP version in use. Cisco has some documents related to how the different IGMP versions work in general and specifically on Cisco devices. For instance, IP ...
  • 94.6k
3 votes

Inter-switch IGMP on a VLAN with two switches, and a multicast source per switch

This is an all too common problem. Snooping requires either a full multicast router, or an igmp querier in the network (one per broadcast domain.) Both periodically send out multicast group requests ...
  • 29.8k
3 votes

Inter-switch IGMP on a VLAN with two switches, and a multicast source per switch

There is a problem with IGMP snooping across switches since the IGMP message on one switch doesn't get send to the other switch, so the switch with the source will not know that the port to the other ...
  • 94.6k
3 votes
Accepted

Multicast timer expires

Normally the router will periodically send a membership query to destination 224.0.0.1 (all hosts multicast group address). Hosts that receive this message will respond with a IGMP membership report ...
3 votes
Accepted

Question Regarding IGMPv3 behaviour: Multicast Router appears to send Membership Report?

From RFC3376 The Internet Group Management Protocol (IGMP) is used by IPv4 systems (hosts and routers) to report their IP multicast group memberships to any neighboring multicast routers. Note ...
  • 1,491
3 votes

Rationale for EXCLUDE mode in mutlicast IGMPv3 / MLDv2

The generic answer to your question would be "exclude mode is to be used when the list of IPs you want to listen to is longer then the list of IPs you do not want to listen to". The most common use ...
  • 4,631
3 votes

Multicast routing on Huawei Quidway 5300 Switches

225.1.1.1 is reserved by IANA so quite possibly the 5300 filters this cast. You should try using an address from one of the ad-hoc blocks 224.0.2.0 - 224.0.255.255, 224.3.0.0-224.4.255.255, or 233....
  • 72.9k
3 votes

OSPF and its use of Multicast

When it comes to OSPF and its use of multicast, am I correct in believing that IGMP forwarding and an IGMP querier is still required within the local segment? OSPF's use of multicast is to a link-...
  • 29.8k
3 votes

IGMP leave group

It depends. If your switching infrastructure is IGMP-aware (IGMP snooping), the IGMP leave group is translated to an Ethernet multicast leave group and that causes the switch port to disable ...
  • 72.9k
3 votes
Accepted

How can MLDv2 work according to the RFCs 3810 and 4606?

1. If not, what does compatibility mode version 1 mean then? According to Mr. Rolland Vida, the author of RFC 3810, with routers/hosts MUST operate in version 1 compatibility mode is meant, that hosts/...
3 votes
Accepted

Trying to understand IGMPv3 Max Response Code algorithm

I think the part you misunderstood in RFC 3376 Section 4.1.1 that you quoted: Max Resp Time = (mant | 0x10) << (exp + 3) I think it could be clearer (not mixing binary and hexadecimal), but as ...
  • 94.6k
3 votes
Accepted

What prevents a device from receiving its own multicast stream, and can it be turned off?

For IEEE 802, including Ethernet, multicast is realized as a filtered broadcast. Both use a group address with the address's I/G bit set to 1. A broadcast is relayed to every active port (IEEE 802.3 ...
  • 72.9k
3 votes
Accepted

PIM-SM over OSPF for mDNS traffic

mDNS uses a link-local multicast address (224.0.0.251) that cannot be sent off-link, so you cannot route mDNS packets. RFC 5771: 4. Local Network Control Block (224.0.0/24) Addresses in the Local ...
  • 94.6k
2 votes

IGMP and multicast forwarding

Routers do not forward multicast unless you have explicitly enabled multicast routing. That requires something like PIM. IGMP is a link-local protocol. Multicast is a form of broadcast, and you ...
  • 94.6k
2 votes
Accepted

Should igmp table lookup misses flood to all ports?

RFC 4541, Considerations for Internet Group Management Protocol (IGMP) and Multicast Listener Discovery (MLD) Snooping Switches, Section 2.1.2. Data Forwarding Rules places that decision squarely on ...
  • 94.6k
2 votes

IGMP Multicast router overrun

Quoting 'cpt_fink': You need something acting as the multicast querier, but not the multicast router. I do not know if this is possible on a TP-Link device. – cpt_fink Feb 18 '15 at 5:19 A ...

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