Re: multicast / CGMP towards the multicast server [7:33964]
Michael, CGMP does not have a concept of the multicast source (unlike the multicast routing protocol) and therefore the fact that the source is on the same link as the router should not change standard CGMP operation -- associating the CAM table with the various multicast groups. - Tom In article , Fears Michael S SSgt 50 CS/SCBBN wrote: If a multicast server is connected to a Cisco Switch running CGMP, and several hosts are connected to the same switch, will a router turn off the switch ports for the users that are not requesting the multicast? So, will CGMP work back towards the multicast server? Fears misconduct and Nondisclosure violations to [EMAIL PROTECTED] Message Posted at: http://www.groupstudy.com/form/read.php?f=7i=34371t=33964 -- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
Re: multicast / CGMP towards the multicast server [7:33964]
Priscilla, I had to search out the answer. I found myself getting up because I couldn't sleep. I believe I found what we were looking for..see Inline. - Original Message - From: Priscilla Oppenheimer To: Sent: Saturday, February 02, 2002 6:22 PM Subject: Re: multicast / CGMP towards the multicast server [7:33964] At 06:18 AM 2/2/02, Nigel Taylor wrote: Even in an design where the host and the server reside on the same VLAN(segment) IGMP and CGMP still provide the ability to control flooding of multicast traffic. Specifically, when the host multicasts the IGMP membership report to the group with the address 224.1.2.3(MAC 0x0100.5E01.0203) and there's no existing mapping in its CAM table, the switch will flood the report on all ports in the VLAN. It's not the membership reports we're concerned about. It's the multicast traffic from the source multicast server. The question can be boiled down to this: It would seem that in this case the membership reports is all that we would need to care about. When you enable CGMP does that mean the switch automatically stops flooding multicast traffic to all devices in the VLAN? Does the switch instead wait for the recipients to send their membership reports, which go to the router and then get converted into CGMP messages from the router to the switch? Only devices that have sent the membership report can receive the traffic. (There could be a problem if it works this way. The multicast server could start sending before anyone joined.) No, when CGMP is enabled on the switch it does not stop the flooding of multicast to all devices in the VLAN. However, as you mention the switch does not wait until the recipients send their membership reports. As you pointed out it's the multicast traffic from the source multicast server that's of interest. In reading what I found, if the switch has no information in it's CAM for the multicast group and the source multicast server begins sending multicast traffic, it hits the switch and does a lookup for the GDA, when it's not found the traffic is flooded out all ports in the VLAN. The question is not about basic IGMP and CGMP behavior. The question has to do with switch behavior in the special case where the source of the multicast traffic is on the same switch and in the same VLAN as the recipients. We're concerned because that sounds like it would cause normal multicast flooding to kick in. For that not to happen, the switch must be smarter than we're thinking. Unfortunately, the switch even with CGMP isn't that smart. The flooding of the multicast traffic would continue until a host, any host on that VLAN sends a IGMP report to the router. The router then create the CGMP packet that will inform the switch of which ports will receive the multicast traffic. All other ports would be blocked except thee router ports. However, any futher attempts to join that existing group would then be limited to port listed in the CAM table that are eligible to recieve the multicast traffic for the group. Once again we're not talking about the membership reports (joins), although what you say is probably true. I wonder if what's also true is that the first membership report causes the switch to then not forward the server's multicast traffic to any devices not listed in the port list in the CAM table for the multicast address. That would make sense. Devices have to send their joins in order to get on the list and get the traffic. Here's the reason for why the IGMP joins are instrumental to this process.. Multicast packets, coming from the source, don't trigger the router to send CGMP self-joins to the switch. Chptr 14, pgs 412-442 of Beau Williamson's book Developing IP Multicast Network provides some really good info on this issue. I couldn't find an answer to our question. Maybe you could?? Thanks. And to add to the question I've been wondering about more ordinary multicasts, like OSPF Hellos and even BPDUs. If you enabled CGMP, would these not get sent to any devices that didn't implement IGMP and sent their membership report? That seems kind of ugly. Maybe it's not an issue because you would only use CGMP on the edge in switches that connect end devices. I think the difference here is as someone posted earlier which defines the multicast well known MAC address as 0x0100.0cdd.. Also, with respect to IGMP capable host, they use the multicast address 224.0.0.2(AllRouter Mcast group) to send their leave messages. Of course this mechanism is that of IGMPv2, since under IGMPv1 there is no support for multicast leave messages. Here's the link to what I found.. http://www.cisco.com/warp/public/105/mcastguide8.html Nigel Priscilla The author does note that flat switched LAN designs will present major problems in gaining/maintaining control of multicast flooding. I guess this really comes down to the network design as with every other
Re: multicast / CGMP towards the multicast server [7:33964]
Priscilla, You're correct in that Fears' real fear at this point has not been answered. ;- In doing some quick research, I found that as you mentioned IGMP(costly) and CGMP(a less costly solution) would assist in providing one the ability to control multicast flooding. This is what I found... Even in an design where the host and the server resides on the same VLAN(segment) IGMP and CGMP still provides the ability to control flooding of multicast traffic. Specifically, when the host multicasts the IGMP membership report to the group with the address 224.1.2.3(MAC 0x0100.5E01.0203) and there's no existing mapping in it's CAM table, the switch will flood the report on all ports in the VLAN. However, any futher attempts to join that existing group would then be limited to port listed in the CAM table that are eligible to recieve the multicast traffic for the group. Chptr 14, pgs 412-442 of Beau Williamson's book Developing IP Multicast Network provides some really good info on this issue. The author does note that flat switched LAN designs will present major problems in gaining/maintaining control of multicast flooding. I guess this really comes down to the network design as with every other aspect of building a scalable and efficient network. Thoughts.. Anyone! Nigel At 09:28 PM 2/1/02, Nigel Taylor wrote: Priscilla, You are correct. Thanks for the added insight. Nigel You are nice to say this, but you know what I realized?! My answer doesn't resolve the quandary either! ;-) I now think that Fears' real fears had to do with the recipients and the server being on the same VLAN. This might cause the switch to forward the multicast traffic before it even checks the results of CGMP. The switch may do its default multicast flooding to ports in a VLAN and just make use of CGMP to learn about other ports. Am I making any sense? It's late. ;-) My guess it that the answer is still that CGMP is smart. Once you configure it, the switch knows to not do its normal multicast flooding and instead wait to hear from the router regarding which ports should receive the multicast flow. Hopefully someone can confirm that. Priscilla - Original Message - From: Priscilla Oppenheimer To: Sent: Friday, February 01, 2002 2:03 PM Subject: Re: multicast / CGMP towards the multicast server [7:33964] No offence, but that answer doesn't remove the quandary. The entire switch is a segment from the router's point of view. The router receives the IGMP Join and now knows that packets for that multicast group must be sent out that interface to that Ethernet segment. All devices on the switch are out that interface, however. What Fears fears is that the router won't be smart enough to tell the switch that not all devices connected to the switch should receive the multicast stream. But fear not, Fears. CGMP is smarter than you might think. Here's how I understand it. Correct me if I'm wrong, please (anyone). As you know, when a host wants to join an IP multicast group, it sends an IGMP Join message. The Join specifies the host's MAC address and the IP multicast group that it wants to join. When a router receives the IGMP Join, it creates a CGMP message that contains the MAC address of the host and the multicast group address. The router sends the CGMP message to a well-known address that all switches listen to. When a Catalyst switch receives the CGMP message from the router, the supervisor engine responds by modifying the forwarding table automatically. In other words, it now knows the specific port that must receive the multicast stream. Other hosts on different ports may Join also, and the switch will add them to the table. This is different from IGMP Snooping, by the way. From what I understand, IGMP Snooping allows the switch to proactively snoop into IGMP packets and figure out which ones are Joins. IGMP Snooping requires more powerful (and more expensive) switching hardware (firmware). Priscilla At 10:18 PM 1/31/02, Nigel Taylor wrote: Michael, Of course this would depend on if the multicast server and the host connected on the same switch was assigned to the same vlan(broadcast domain). Just some quick points to mention.. Routers by default will not forward multicast traffic. However, if you enabled a multicast routing protocol(PIM, DVMRP) then this is possible. The important thing here is that IGMP is used by hosts to inform routers of their intent to become part of a multicast stream. This depends on your implementation of the multicast protocol. IGMPv2 has been improved to support leaves from a multicast group which is not supported in IGMPv1. This way the host is able to notify the source of it's intent to leave the multicast group. This is will allow the routers to prune
Re: multicast / CGMP towards the multicast server [7:33964]
Added note for anyone who may be interested:: The well-known CGMP multicast MAC address is: 0x0100,0cdd,, dj Nigel Taylor wrote in message [EMAIL PROTECTED]">news:[EMAIL PROTECTED]... Priscilla, You're correct in that Fears' real fear at this point has not been answered. ;- In doing some quick research, I found that as you mentioned IGMP(costly) and CGMP(a less costly solution) would assist in providing one the ability to control multicast flooding. This is what I found... Even in an design where the host and the server resides on the same VLAN(segment) IGMP and CGMP still provides the ability to control flooding of multicast traffic. Specifically, when the host multicasts the IGMP membership report to the group with the address 224.1.2.3(MAC 0x0100.5E01.0203) and there's no existing mapping in it's CAM table, the switch will flood the report on all ports in the VLAN. However, any futher attempts to join that existing group would then be limited to port listed in the CAM table that are eligible to recieve the multicast traffic for the group. Chptr 14, pgs 412-442 of Beau Williamson's book Developing IP Multicast Network provides some really good info on this issue. The author does note that flat switched LAN designs will present major problems in gaining/maintaining control of multicast flooding. I guess this really comes down to the network design as with every other aspect of building a scalable and efficient network. Thoughts.. Anyone! Nigel At 09:28 PM 2/1/02, Nigel Taylor wrote: Priscilla, You are correct. Thanks for the added insight. Nigel You are nice to say this, but you know what I realized?! My answer doesn't resolve the quandary either! ;-) I now think that Fears' real fears had to do with the recipients and the server being on the same VLAN. This might cause the switch to forward the multicast traffic before it even checks the results of CGMP. The switch may do its default multicast flooding to ports in a VLAN and just make use of CGMP to learn about other ports. Am I making any sense? It's late. ;-) My guess it that the answer is still that CGMP is smart. Once you configure it, the switch knows to not do its normal multicast flooding and instead wait to hear from the router regarding which ports should receive the multicast flow. Hopefully someone can confirm that. Priscilla - Original Message - From: Priscilla Oppenheimer To: Sent: Friday, February 01, 2002 2:03 PM Subject: Re: multicast / CGMP towards the multicast server [7:33964] No offence, but that answer doesn't remove the quandary. The entire switch is a segment from the router's point of view. The router receives the IGMP Join and now knows that packets for that multicast group must be sent out that interface to that Ethernet segment. All devices on the switch are out that interface, however. What Fears fears is that the router won't be smart enough to tell the switch that not all devices connected to the switch should receive the multicast stream. But fear not, Fears. CGMP is smarter than you might think. Here's how I understand it. Correct me if I'm wrong, please (anyone). As you know, when a host wants to join an IP multicast group, it sends an IGMP Join message. The Join specifies the host's MAC address and the IP multicast group that it wants to join. When a router receives the IGMP Join, it creates a CGMP message that contains the MAC address of the host and the multicast group address. The router sends the CGMP message to a well-known address that all switches listen to. When a Catalyst switch receives the CGMP message from the router, the supervisor engine responds by modifying the forwarding table automatically. In other words, it now knows the specific port that must receive the multicast stream. Other hosts on different ports may Join also, and the switch will add them to the table. This is different from IGMP Snooping, by the way. From what I understand, IGMP Snooping allows the switch to proactively snoop into IGMP packets and figure out which ones are Joins. IGMP Snooping requires more powerful (and more expensive) switching hardware (firmware). Priscilla At 10:18 PM 1/31/02, Nigel Taylor wrote: Michael, Of course this would depend on if the multicast server and the host connected on the same switch was assigned to the same vlan(broadcast domain). Just some quick points to mention.. Routers by default will not forward multicast traffic. However, if you enabled a multicast routing protocol(PIM, DVMRP) then this is possible. The important thing here is that IGMP is used by hosts to inform routers of their intent to become part of a multicas
Re: multicast / CGMP towards the multicast server [7:33964]
At 06:18 AM 2/2/02, Nigel Taylor wrote: Even in an design where the host and the server reside on the same VLAN(segment) IGMP and CGMP still provide the ability to control flooding of multicast traffic. Specifically, when the host multicasts the IGMP membership report to the group with the address 224.1.2.3(MAC 0x0100.5E01.0203) and there's no existing mapping in its CAM table, the switch will flood the report on all ports in the VLAN. It's not the membership reports we're concerned about. It's the multicast traffic from the source multicast server. The question can be boiled down to this: When you enable CGMP does that mean the switch automatically stops flooding multicast traffic to all devices in the VLAN? Does the switch instead wait for the recipients to send their membership reports, which go to the router and then get converted into CGMP messages from the router to the switch? Only devices that have sent the membership report can receive the traffic. (There could be a problem if it works this way. The multicast server could start sending before anyone joined.) The question is not about basic IGMP and CGMP behavior. The question has to do with switch behavior in the special case where the source of the multicast traffic is on the same switch and in the same VLAN as the recipients. We're concerned because that sounds like it would cause normal multicast flooding to kick in. For that not to happen, the switch must be smarter than we're thinking. However, any futher attempts to join that existing group would then be limited to port listed in the CAM table that are eligible to recieve the multicast traffic for the group. Once again we're not talking about the membership reports (joins), although what you say is probably true. I wonder if what's also true is that the first membership report causes the switch to then not forward the server's multicast traffic to any devices not listed in the port list in the CAM table for the multicast address. That would make sense. Devices have to send their joins in order to get on the list and get the traffic. Chptr 14, pgs 412-442 of Beau Williamson's book Developing IP Multicast Network provides some really good info on this issue. I couldn't find an answer to our question. Maybe you could?? Thanks. And to add to the question I've been wondering about more ordinary multicasts, like OSPF Hellos and even BPDUs. If you enabled CGMP, would these not get sent to any devices that didn't implement IGMP and sent their membership report? That seems kind of ugly. Maybe it's not an issue because you would only use CGMP on the edge in switches that connect end devices. Priscilla The author does note that flat switched LAN designs will present major problems in gaining/maintaining control of multicast flooding. I guess this really comes down to the network design as with every other aspect of building a scalable and efficient network. Thoughts.. Anyone! Nigel At 09:28 PM 2/1/02, Nigel Taylor wrote: Priscilla, You are correct. Thanks for the added insight. Nigel You are nice to say this, but you know what I realized?! My answer doesn't resolve the quandary either! ;-) I now think that Fears' real fears had to do with the recipients and the server being on the same VLAN. This might cause the switch to forward the multicast traffic before it even checks the results of CGMP. The switch may do its default multicast flooding to ports in a VLAN and just make use of CGMP to learn about other ports. Am I making any sense? It's late. ;-) My guess it that the answer is still that CGMP is smart. Once you configure it, the switch knows to not do its normal multicast flooding and instead wait to hear from the router regarding which ports should receive the multicast flow. Hopefully someone can confirm that. Priscilla - Original Message - From: Priscilla Oppenheimer To: Sent: Friday, February 01, 2002 2:03 PM Subject: Re: multicast / CGMP towards the multicast server [7:33964] No offence, but that answer doesn't remove the quandary. The entire switch is a segment from the router's point of view. The router receives the IGMP Join and now knows that packets for that multicast group must be sent out that interface to that Ethernet segment. All devices on the switch are out that interface, however. What Fears fears is that the router won't be smart enough to tell the switch that not all devices connected to the switch should receive the multicast stream. But fear not, Fears. CGMP is smarter than you might think. Here's how I understand it. Correct me if I'm wrong, please (anyone). As you know, when a host wants to join an IP multicast group, it sends an IGMP Join message. The Join specifies the host's MAC address and the IP multicast group that it wants to join. When a router receives
Re: multicast / CGMP towards the multicast server [7:33964]
Like I said before, as long as you have a router connected to that segment (VLAN), multicast flooding will be constrained to the ports that have sent membership report. Non-registered clients will not be able to receive the multicast traffic, even though they are on the same VLAN as the sender. The router dynamically modifies the switch MAC table through CGMP messages. CM - Original Message - From: Priscilla Oppenheimer To: Sent: Saturday, February 02, 2002 11:22 PM Subject: Re: multicast / CGMP towards the multicast server [7:33964] At 06:18 AM 2/2/02, Nigel Taylor wrote: Even in an design where the host and the server reside on the same VLAN(segment) IGMP and CGMP still provide the ability to control flooding of multicast traffic. Specifically, when the host multicasts the IGMP membership report to the group with the address 224.1.2.3(MAC 0x0100.5E01.0203) and there's no existing mapping in its CAM table, the switch will flood the report on all ports in the VLAN. It's not the membership reports we're concerned about. It's the multicast traffic from the source multicast server. The question can be boiled down to this: When you enable CGMP does that mean the switch automatically stops flooding multicast traffic to all devices in the VLAN? Does the switch instead wait for the recipients to send their membership reports, which go to the router and then get converted into CGMP messages from the router to the switch? Only devices that have sent the membership report can receive the traffic. (There could be a problem if it works this way. The multicast server could start sending before anyone joined.) The question is not about basic IGMP and CGMP behavior. The question has to do with switch behavior in the special case where the source of the multicast traffic is on the same switch and in the same VLAN as the recipients. We're concerned because that sounds like it would cause normal multicast flooding to kick in. For that not to happen, the switch must be smarter than we're thinking. However, any futher attempts to join that existing group would then be limited to port listed in the CAM table that are eligible to recieve the multicast traffic for the group. Once again we're not talking about the membership reports (joins), although what you say is probably true. I wonder if what's also true is that the first membership report causes the switch to then not forward the server's multicast traffic to any devices not listed in the port list in the CAM table for the multicast address. That would make sense. Devices have to send their joins in order to get on the list and get the traffic. Chptr 14, pgs 412-442 of Beau Williamson's book Developing IP Multicast Network provides some really good info on this issue. I couldn't find an answer to our question. Maybe you could?? Thanks. And to add to the question I've been wondering about more ordinary multicasts, like OSPF Hellos and even BPDUs. If you enabled CGMP, would these not get sent to any devices that didn't implement IGMP and sent their membership report? That seems kind of ugly. Maybe it's not an issue because you would only use CGMP on the edge in switches that connect end devices. Priscilla The author does note that flat switched LAN designs will present major problems in gaining/maintaining control of multicast flooding. I guess this really comes down to the network design as with every other aspect of building a scalable and efficient network. Thoughts.. Anyone! Nigel At 09:28 PM 2/1/02, Nigel Taylor wrote: Priscilla, You are correct. Thanks for the added insight. Nigel You are nice to say this, but you know what I realized?! My answer doesn't resolve the quandary either! ;-) I now think that Fears' real fears had to do with the recipients and the server being on the same VLAN. This might cause the switch to forward the multicast traffic before it even checks the results of CGMP. The switch may do its default multicast flooding to ports in a VLAN and just make use of CGMP to learn about other ports. Am I making any sense? It's late. ;-) My guess it that the answer is still that CGMP is smart. Once you configure it, the switch knows to not do its normal multicast flooding and instead wait to hear from the router regarding which ports should receive the multicast flow. Hopefully someone can confirm that. Priscilla - Original Message - From: Priscilla Oppenheimer To: Sent: Friday, February 01, 2002 2:03 PM Subject: Re: multicast / CGMP towards the multicast server [7:33964] No offence, but that answer doesn't remove the quandary. The entire switch is a segment from the router's point of view. The router receives the IGMP Join and now knows that packets for that multicast group must be sent out that interface
RE: multicast / CGMP towards the multicast server [7:33964]
Nigel, Thanks, Yes the switch and users are all on the same VLAN. PIM and IGMP are working fine across the router and into other CGMP enable switches. The thing I was not sure of, was: if I have a server multicasting on the same switch/VLAN as other users, can I prevent the multicast stream from flooding the broadcast domain that the server is in? I was asked this question and my answer was no. I thought it was just poor design to have the multicast server on the same VLAN as the users who are not using it. Maybe I'm wrong?? -Original Message- From: Nigel Taylor [mailto:[EMAIL PROTECTED]] Sent: Thursday, January 31, 2002 8:19 PM To: [EMAIL PROTECTED] Subject: Re: multicast / CGMP towards the multicast server [7:33964] Michael, Of course this would depend on if the multicast server and the host connected on the same switch was assigned to the same vlan(broadcast domain). Just some quick points to mention.. Routers by default will not forward multicast traffic. However, if you enabled a multicast routing protocol(PIM, DVMRP) then this is possible. The important thing here is that IGMP is used by hosts to inform routers of their intent to become part of a multicast stream. This depends on your implementation of the multicast protocol. IGMPv2 has been improved to support leaves from a multicast group which is not supported in IGMPv1. This way the host is able to notify the source of it's intent to leave the multicast group. This is will allow the routers to prune the multicast traffic from the segment removing the unnecessary traffic, providing no other host on the segment remains a member of the multicast stream A good title as recommended by a number of folks on the list is Developing IP Multicast Networks Author: Beau Williamson. ISBN: 157870779 HTH Nigel Original Message - From: Fears Michael S SSgt 50 CS/SCBBN To: Sent: Thursday, January 31, 2002 4:59 PM Subject: multicast / CGMP towards the multicast server [7:33964] If a multicast server is connected to a Cisco Switch running CGMP, and several hosts are connected to the same switch, will a router turn off the switch ports for the users that are not requesting the multicast? So, will CGMP work back towards the multicast server? Fears Message Posted at: http://www.groupstudy.com/form/read.php?f=7i=34052t=33964 -- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
Re: multicast / CGMP towards the multicast server [7:33964]
As long as there is a multicast router connected to the switch, and CGMP is enabled on that switch, then yes, the router will control flooding of multicast traffic on the switch ports. CM - Original Message - From: Fears Michael S SSgt 50 CS/SCBBN To: Sent: Friday, February 01, 2002 1:57 PM Subject: RE: multicast / CGMP towards the multicast server [7:33964] Nigel, Thanks, Yes the switch and users are all on the same VLAN. PIM and IGMP are working fine across the router and into other CGMP enable switches. The thing I was not sure of, was: if I have a server multicasting on the same switch/VLAN as other users, can I prevent the multicast stream from flooding the broadcast domain that the server is in? I was asked this question and my answer was no. I thought it was just poor design to have the multicast server on the same VLAN as the users who are not using it. Maybe I'm wrong?? -Original Message- From: Nigel Taylor [mailto:[EMAIL PROTECTED]] Sent: Thursday, January 31, 2002 8:19 PM To: [EMAIL PROTECTED] Subject: Re: multicast / CGMP towards the multicast server [7:33964] Michael, Of course this would depend on if the multicast server and the host connected on the same switch was assigned to the same vlan(broadcast domain). Just some quick points to mention.. Routers by default will not forward multicast traffic. However, if you enabled a multicast routing protocol(PIM, DVMRP) then this is possible. The important thing here is that IGMP is used by hosts to inform routers of their intent to become part of a multicast stream. This depends on your implementation of the multicast protocol. IGMPv2 has been improved to support leaves from a multicast group which is not supported in IGMPv1. This way the host is able to notify the source of it's intent to leave the multicast group. This is will allow the routers to prune the multicast traffic from the segment removing the unnecessary traffic, providing no other host on the segment remains a member of the multicast stream A good title as recommended by a number of folks on the list is Developing IP Multicast Networks Author: Beau Williamson. ISBN: 157870779 HTH Nigel Original Message - From: Fears Michael S SSgt 50 CS/SCBBN To: Sent: Thursday, January 31, 2002 4:59 PM Subject: multicast / CGMP towards the multicast server [7:33964] If a multicast server is connected to a Cisco Switch running CGMP, and several hosts are connected to the same switch, will a router turn off the switch ports for the users that are not requesting the multicast? So, will CGMP work back towards the multicast server? Fears Message Posted at: http://www.groupstudy.com/form/read.php?f=7i=34055t=33964 -- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
RE: multicast / CGMP towards the multicast server [7:33964]
When a multicast reciever wishes to recieve multicast traffic it must send an IGMP join for the multicast group. CGMP/IGMP snooping get in the way of this and makes sure the stream only goes to needed ports. A multicast sender doesn't need to send an IGMP join to the router to start sending multicasts (that can't be a requirement, because if it was what would happen on multicast networks without routers?) A sender simply starts sending packets. Because a sender doesn't send IGMP joins CGMP and IGMP snooping cannot function. Kinda sucks huh? If your intrested I'm working on an open source multicast project that simulates multicast traffic at http://sourceforge.net/projects/mc-mint/ If you want you can look at the souce and you'll see the sender function doesn't use IGMP joins. Mike --- Mike Bernico [EMAIL PROTECTED] Illinois Century Network http://www.illinois.net (217) 557-6555 -Original Message- From: Fears Michael S SSgt 50 CS/SCBBN [mailto:[EMAIL PROTECTED]] Sent: Friday, February 01, 2002 7:58 AM To: [EMAIL PROTECTED] Subject: RE: multicast / CGMP towards the multicast server [7:33964] Nigel, Thanks, Yes the switch and users are all on the same VLAN. PIM and IGMP are working fine across the router and into other CGMP enable switches. The thing I was not sure of, was: if I have a server multicasting on the same switch/VLAN as other users, can I prevent the multicast stream from flooding the broadcast domain that the server is in? I was asked this question and my answer was no. I thought it was just poor design to have the multicast server on the same VLAN as the users who are not using it. Maybe I'm wrong?? -Original Message- From: Nigel Taylor [mailto:[EMAIL PROTECTED]] Sent: Thursday, January 31, 2002 8:19 PM To: [EMAIL PROTECTED] Subject: Re: multicast / CGMP towards the multicast server [7:33964] Michael, Of course this would depend on if the multicast server and the host connected on the same switch was assigned to the same vlan(broadcast domain). Just some quick points to mention.. Routers by default will not forward multicast traffic. However, if you enabled a multicast routing protocol(PIM, DVMRP) then this is possible. The important thing here is that IGMP is used by hosts to inform routers of their intent to become part of a multicast stream. This depends on your implementation of the multicast protocol. IGMPv2 has been improved to support leaves from a multicast group which is not supported in IGMPv1. This way the host is able to notify the source of it's intent to leave the multicast group. This is will allow the routers to prune the multicast traffic from the segment removing the unnecessary traffic, providing no other host on the segment remains a member of the multicast stream A good title as recommended by a number of folks on the list is Developing IP Multicast Networks Author: Beau Williamson. ISBN: 157870779 HTH Nigel Original Message - From: Fears Michael S SSgt 50 CS/SCBBN To: Sent: Thursday, January 31, 2002 4:59 PM Subject: multicast / CGMP towards the multicast server [7:33964] If a multicast server is connected to a Cisco Switch running CGMP, and several hosts are connected to the same switch, will a router turn off the switch ports for the users that are not requesting the multicast? So, will CGMP work back towards the multicast server? Fears Message Posted at: http://www.groupstudy.com/form/read.php?f=7i=34061t=33964 -- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
Re: multicast / CGMP towards the multicast server [7:33964]
No offence, but that answer doesn't remove the quandary. The entire switch is a segment from the router's point of view. The router receives the IGMP Join and now knows that packets for that multicast group must be sent out that interface to that Ethernet segment. All devices on the switch are out that interface, however. What Fears fears is that the router won't be smart enough to tell the switch that not all devices connected to the switch should receive the multicast stream. But fear not, Fears. CGMP is smarter than you might think. Here's how I understand it. Correct me if I'm wrong, please (anyone). As you know, when a host wants to join an IP multicast group, it sends an IGMP Join message. The Join specifies the host's MAC address and the IP multicast group that it wants to join. When a router receives the IGMP Join, it creates a CGMP message that contains the MAC address of the host and the multicast group address. The router sends the CGMP message to a well-known address that all switches listen to. When a Catalyst switch receives the CGMP message from the router, the supervisor engine responds by modifying the forwarding table automatically. In other words, it now knows the specific port that must receive the multicast stream. Other hosts on different ports may Join also, and the switch will add them to the table. This is different from IGMP Snooping, by the way. From what I understand, IGMP Snooping allows the switch to proactively snoop into IGMP packets and figure out which ones are Joins. IGMP Snooping requires more powerful (and more expensive) switching hardware (firmware). Priscilla At 10:18 PM 1/31/02, Nigel Taylor wrote: Michael, Of course this would depend on if the multicast server and the host connected on the same switch was assigned to the same vlan(broadcast domain). Just some quick points to mention.. Routers by default will not forward multicast traffic. However, if you enabled a multicast routing protocol(PIM, DVMRP) then this is possible. The important thing here is that IGMP is used by hosts to inform routers of their intent to become part of a multicast stream. This depends on your implementation of the multicast protocol. IGMPv2 has been improved to support leaves from a multicast group which is not supported in IGMPv1. This way the host is able to notify the source of it's intent to leave the multicast group. This is will allow the routers to prune the multicast traffic from the segment removing the unnecessary traffic, providing no other host on the segment remains a member of the multicast stream A good title as recommended by a number of folks on the list is Developing IP Multicast Networks Author: Beau Williamson. ISBN: 157870779 HTH Nigel Original Message - From: Fears Michael S SSgt 50 CS/SCBBN To: Sent: Thursday, January 31, 2002 4:59 PM Subject: multicast / CGMP towards the multicast server [7:33964] If a multicast server is connected to a Cisco Switch running CGMP, and several hosts are connected to the same switch, will a router turn off the switch ports for the users that are not requesting the multicast? So, will CGMP work back towards the multicast server? Fears Priscilla Oppenheimer http://www.priscilla.com Message Posted at: http://www.groupstudy.com/form/read.php?f=7i=34099t=33964 -- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
Re: multicast / CGMP towards the multicast server [7:33964]
Priscilla, You are correct. Thanks for the added insight. Nigel - Original Message - From: Priscilla Oppenheimer To: Sent: Friday, February 01, 2002 2:03 PM Subject: Re: multicast / CGMP towards the multicast server [7:33964] No offence, but that answer doesn't remove the quandary. The entire switch is a segment from the router's point of view. The router receives the IGMP Join and now knows that packets for that multicast group must be sent out that interface to that Ethernet segment. All devices on the switch are out that interface, however. What Fears fears is that the router won't be smart enough to tell the switch that not all devices connected to the switch should receive the multicast stream. But fear not, Fears. CGMP is smarter than you might think. Here's how I understand it. Correct me if I'm wrong, please (anyone). As you know, when a host wants to join an IP multicast group, it sends an IGMP Join message. The Join specifies the host's MAC address and the IP multicast group that it wants to join. When a router receives the IGMP Join, it creates a CGMP message that contains the MAC address of the host and the multicast group address. The router sends the CGMP message to a well-known address that all switches listen to. When a Catalyst switch receives the CGMP message from the router, the supervisor engine responds by modifying the forwarding table automatically. In other words, it now knows the specific port that must receive the multicast stream. Other hosts on different ports may Join also, and the switch will add them to the table. This is different from IGMP Snooping, by the way. From what I understand, IGMP Snooping allows the switch to proactively snoop into IGMP packets and figure out which ones are Joins. IGMP Snooping requires more powerful (and more expensive) switching hardware (firmware). Priscilla At 10:18 PM 1/31/02, Nigel Taylor wrote: Michael, Of course this would depend on if the multicast server and the host connected on the same switch was assigned to the same vlan(broadcast domain). Just some quick points to mention.. Routers by default will not forward multicast traffic. However, if you enabled a multicast routing protocol(PIM, DVMRP) then this is possible. The important thing here is that IGMP is used by hosts to inform routers of their intent to become part of a multicast stream. This depends on your implementation of the multicast protocol. IGMPv2 has been improved to support leaves from a multicast group which is not supported in IGMPv1. This way the host is able to notify the source of it's intent to leave the multicast group. This is will allow the routers to prune the multicast traffic from the segment removing the unnecessary traffic, providing no other host on the segment remains a member of the multicast stream A good title as recommended by a number of folks on the list is Developing IP Multicast Networks Author: Beau Williamson. ISBN: 157870779 HTH Nigel Original Message - From: Fears Michael S SSgt 50 CS/SCBBN To: Sent: Thursday, January 31, 2002 4:59 PM Subject: multicast / CGMP towards the multicast server [7:33964] If a multicast server is connected to a Cisco Switch running CGMP, and several hosts are connected to the same switch, will a router turn off the switch ports for the users that are not requesting the multicast? So, will CGMP work back towards the multicast server? Fears Priscilla Oppenheimer http://www.priscilla.com Message Posted at: http://www.groupstudy.com/form/read.php?f=7i=34159t=33964 -- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
Re: multicast / CGMP towards the multicast server [7:33964]
At 09:28 PM 2/1/02, Nigel Taylor wrote: Priscilla, You are correct. Thanks for the added insight. Nigel You are nice to say this, but you know what I realized?! My answer doesn't resolve the quandary either! ;-) I now think that Fears' real fears had to do with the recipients and the server being on the same VLAN. This might cause the switch to forward the multicast traffic before it even checks the results of CGMP. The switch may do its default multicast flooding to ports in a VLAN and just make use of CGMP to learn about other ports. Am I making any sense? It's late. ;-) My guess it that the answer is still that CGMP is smart. Once you configure it, the switch knows to not do its normal multicast flooding and instead wait to hear from the router regarding which ports should receive the multicast flow. Hopefully someone can confirm that. Priscilla - Original Message - From: Priscilla Oppenheimer To: Sent: Friday, February 01, 2002 2:03 PM Subject: Re: multicast / CGMP towards the multicast server [7:33964] No offence, but that answer doesn't remove the quandary. The entire switch is a segment from the router's point of view. The router receives the IGMP Join and now knows that packets for that multicast group must be sent out that interface to that Ethernet segment. All devices on the switch are out that interface, however. What Fears fears is that the router won't be smart enough to tell the switch that not all devices connected to the switch should receive the multicast stream. But fear not, Fears. CGMP is smarter than you might think. Here's how I understand it. Correct me if I'm wrong, please (anyone). As you know, when a host wants to join an IP multicast group, it sends an IGMP Join message. The Join specifies the host's MAC address and the IP multicast group that it wants to join. When a router receives the IGMP Join, it creates a CGMP message that contains the MAC address of the host and the multicast group address. The router sends the CGMP message to a well-known address that all switches listen to. When a Catalyst switch receives the CGMP message from the router, the supervisor engine responds by modifying the forwarding table automatically. In other words, it now knows the specific port that must receive the multicast stream. Other hosts on different ports may Join also, and the switch will add them to the table. This is different from IGMP Snooping, by the way. From what I understand, IGMP Snooping allows the switch to proactively snoop into IGMP packets and figure out which ones are Joins. IGMP Snooping requires more powerful (and more expensive) switching hardware (firmware). Priscilla At 10:18 PM 1/31/02, Nigel Taylor wrote: Michael, Of course this would depend on if the multicast server and the host connected on the same switch was assigned to the same vlan(broadcast domain). Just some quick points to mention.. Routers by default will not forward multicast traffic. However, if you enabled a multicast routing protocol(PIM, DVMRP) then this is possible. The important thing here is that IGMP is used by hosts to inform routers of their intent to become part of a multicast stream. This depends on your implementation of the multicast protocol. IGMPv2 has been improved to support leaves from a multicast group which is not supported in IGMPv1. This way the host is able to notify the source of it's intent to leave the multicast group. This is will allow the routers to prune the multicast traffic from the segment removing the unnecessary traffic, providing no other host on the segment remains a member of the multicast stream A good title as recommended by a number of folks on the list is Developing IP Multicast Networks Author: Beau Williamson. ISBN: 157870779 HTH Nigel Original Message - From: Fears Michael S SSgt 50 CS/SCBBN To: Sent: Thursday, January 31, 2002 4:59 PM Subject: multicast / CGMP towards the multicast server [7:33964] If a multicast server is connected to a Cisco Switch running CGMP, and several hosts are connected to the same switch, will a router turn off the switch ports for the users that are not requesting the multicast? So, will CGMP work back towards the multicast server? Fears Priscilla Oppenheimer http://www.priscilla.com Priscilla Oppenheimer http://www.priscilla.com Message Posted at: http://www.groupstudy.com/form/read.php?f=7i=34162t=33964 -- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
Re: multicast / CGMP towards the multicast server [7:33964]
If by turn off the port you mean not send the multicast stream to that port then yes. Assuming you have it configured correctly. Fears Michael S SSgt 50 CS/SCBBN wrote in message [EMAIL PROTECTED]">news:[EMAIL PROTECTED]... If a multicast server is connected to a Cisco Switch running CGMP, and several hosts are connected to the same switch, will a router turn off the switch ports for the users that are not requesting the multicast? So, will CGMP work back towards the multicast server? Fears Message Posted at: http://www.groupstudy.com/form/read.php?f=7i=33983t=33964 -- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
Re: multicast / CGMP towards the multicast server [7:33964]
Michael, Of course this would depend on if the multicast server and the host connected on the same switch was assigned to the same vlan(broadcast domain). Just some quick points to mention.. Routers by default will not forward multicast traffic. However, if you enabled a multicast routing protocol(PIM, DVMRP) then this is possible. The important thing here is that IGMP is used by hosts to inform routers of their intent to become part of a multicast stream. This depends on your implementation of the multicast protocol. IGMPv2 has been improved to support leaves from a multicast group which is not supported in IGMPv1. This way the host is able to notify the source of it's intent to leave the multicast group. This is will allow the routers to prune the multicast traffic from the segment removing the unnecessary traffic, providing no other host on the segment remains a member of the multicast stream A good title as recommended by a number of folks on the list is Developing IP Multicast Networks Author: Beau Williamson. ISBN: 157870779 HTH Nigel Original Message - From: Fears Michael S SSgt 50 CS/SCBBN To: Sent: Thursday, January 31, 2002 4:59 PM Subject: multicast / CGMP towards the multicast server [7:33964] If a multicast server is connected to a Cisco Switch running CGMP, and several hosts are connected to the same switch, will a router turn off the switch ports for the users that are not requesting the multicast? So, will CGMP work back towards the multicast server? Fears Message Posted at: http://www.groupstudy.com/form/read.php?f=7i=34001t=33964 -- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
