Hot answers tagged

19

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 need to configure one (or more) igmp queriers. This ensures group membership reports are flood through the network periodically to keep the forwarding ...


11

The reason that it doesn't have to leave the LAN is that IGMP (or MLD if you use IPv6) only talks to the multicast router on the LAN. The multicast router will take care of the routing.


9

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 multicast group is a link-local multicast that gets sent to every switch interface, even with IGMP snooping enabled on the switch. OSPF only uses multicast on ...


8

I've kept digging around the internet....and I think I've answered my own question. Now I need to go back to the application/device owners/developers and see what we can do or further lock these devices down to their own VLAN. Please leave comments or answers with any further advice. RFC 4541 2.1.2: 1) Packets with a destination IP address outside 224.0.0....


7

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. Multicast routing is very different than unicast routing, and it must be specifically configured on all the routers between networks in order for multicast ...


6

There is another caveat: Depending on platform, the switch will punt all link-local multicast to the CPU. This includes for example OSPF traffic. I noticed this on Ciscos Catalyst 4500 which will send all 224.0.0.x traffic to the CPU. When the CPU is busy it will drop the packets, including your OSPF packets. Have fun debugging why your OSPF session(s) drop....


5

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 interface of the active Kemp unit. If this box is checked, then the MAC address of the VIP is a VRRP MAC. As you mentioned above the VRRP RFC states that the ...


5

TTL == 1 means stay on this network; it will not be forwarded by any router. This is true of multicast and unicast. The purpose for doing this with multicast is to limit how far the message can spread. For example, 224.0.0.1 (All Systems on this Subnet) is required to have a TTL of 1 to keep it "on this subnet". 224.0.1.1 (NTP) can have as high a TTL as you ...


5

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


4

Is it possible to get a traffic from a multicast address with specific destination port using IGMP? Short Answer: You have three decent choices: Ask some senders / listeners to change their group Deploy IGMPv3 with PIM-SSM Deny certain UDP ports with an extended ACL (example: the Catalyst 4500 calls this a Port ACL... since it requires manual intervention ...


4

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 use "ip igmp static-group" on their side.


4

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 opening network definition stanza. The default is "no" - which, unfortunately, breaks both IPv6 and multicast for IPv4. This is actually laid out in a RedHat Bug ...


4

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. You do not get IGMP snooping to cross VLANs, and multicast doesn't cross VLANs unless you enable multicast routing.


4

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 traverse both hops in your topology.


4

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 224.0.0.0/24, just as Ron explained. However - and I believe that's the part you didn't consider - a host can still discard these multicast earlier than if they were ...


3

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 that an IP multicast router may itself be a member of one or more multicast groups, in which case it performs both the "multicast ...


3

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 case is actually the most extreme case: listening for packets from any source. This means using exclude mode with an empty exclude list. Since IGMPv1 and v2 do ...


3

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 to tell the router that they are still interested in receiving the multicast traffic. When the router receives the membership report, it’s expiry timer will be ...


3

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 Thanks to everyone!!


3

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 Multicast Technology Overview, Intradomain Multicast Protocols, Internet Group Management Protocol (IGMP). The real answers are found in the RFCs: RFC 1112, ...


3

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. You should be able to do this ip access-list standard iptv permit 234.X.X.X ip pim rp-address X.X.X.X iptv where x.x.x.x is the IP of vlan 10 or any other ...


3

We should be able to configure member leave time in the switch. For Cisco boxes, we can configured this timer globally or on a vlan-basis: http://www.cisco.com/en/US/docs/switches/lan/catalyst4500/12.2/50sg/configuration/guide/multi.html#wp1126514 . ##To configure globally ip igmp snooping last-member-query-interval time ##To configure on a per-vlan ...


3

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 cannot normally send broadcasts across routers. In order to be able to route multicast, you need some controls to prevent it from being sent where it is not wanted. ...


3

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 233.252.0.0-233.255.255.255.


3

Multicast is clearly working for group 239.255.255.250: Both Server and Client PCs have joined the group (through IGMP) Both are sending to the group, can see (S,G) entries: (192.168.1.252, 239.255.255.250) - Server sending to group (192.168.0.253, 239.255.255.250) - Client sending to group These (S,G) entries have correct Upstream and Downstream ...


3

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-local scope group, with IP TTL set to 1 to ensure it says link-local. [ 224.0.0.5 and 224.0.0.6 (RFC2328 pp.185-186)] OSPF aside, for the multicast pruning ...


3

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 forwarding for that group. However, the next query would rejoin the port to the IGMP group. Without switch IGMP support, multicasts are flooded like broadcasts, making ...


3

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/router should have version compatibility enabled. If MLDv2 is implemented in routers/host, they will start in Compatibility Mode MLDv2 (so the Compatibility ...


3

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 far as I can gather: (1001 OR 10000) = 11001 -> 11001^11 = 11001000 = Decimal 200 You must OR 0x10 to the matissa, which is one binary digit larger than ...


3

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 clause 3.2.3.1) but the one is was received on (a MAC bridge must not cause a loop as per IEEE 802.1D clause 7.1.1). A multicast is modelled as (optionally) ...


Only top voted, non community-wiki answers of a minimum length are eligible