Multicast packets on trunks

I have two switches connected via ISL trunks. Multicast packets can't get from one switch to the other even though the source and destination are on the same VLAN and is trunked. Shouldn't the switch just pass it on like other layer 2 frames?

The difference is that EIGRP speakers have signaled their intent to listen to multicast traffic. So IGMP Snooping functionality relays that multicast traffic to them.
See
http://www.cisco.com/en/US/products/hw/switches/ps708/products_tech_note09186a008059a9df.shtml
for several solutions to this issue.
Yet another reason to not like NLB....
Michael

Similar Messages

"Multicast" Across a Trunk port

I have a pair of Nokia firewalls connected to two 4006 switches running 7.6.3 code. The firewalls have a multicast virutal address that doesn't seem to pass across an etherchannel trunk between the switches even though the vlan they are in is being forwarded across the trunk. Do you know if a dot1q trunk would block a multicast packet from a Nokia firewall from passing ?

Hi :
Basically , by default multicast is only forwarded to the router ports or where an IGMP request is received. Now you have a Cat4000 and it has CGMP turned on by default . As long as it does not detect any router ports , multicast should basically be flooded in the entire vlan. In your case , multicast not being flooded makes me think the switch is detecting a multicast router at some other port other then the trunk port and certainly not receiving a CGMP join from that router for this particular group.
Here is a hack that you can use.
set multicast router
where mod/port is a trunk port .
Second thing is youc an disable CGMP only if you do not have other multicast traffic in your network and only traffic is this low volume keepalive traffic between the firewalls so that this traffic will be flooded in the entire vlan on both switches.
set cgmp disable
Hope this helps.
Salman Z.

Lost Multicast Packets on 1 JVM Only

Hi,
I have a cluster of 4 JVM's which is distributed across 2 physical servers. This is running on a windows 32 bit environment.
Machine1: JVM01/JVM02
Machine2: JVM03/JVM04
JVM03 is losting lots of multicast packets, where the others are not. 1600 since 22:30 last night, so in about 12 hours.
I haven't noticed any side effects to the application of this happening, but I can't figure out why if JVM03 is losing them, I don't see them being lost on JVM04 as they are on the same physical hardware.
if it was plugged into a dodgy switch port, then I would expect both JVM's to be affected.
Anyone any ideas?
Pete

Are you running any add-ons that might change the appearance of the page, e.g., add-ons that block ads, Flash, scripts, etc.?
Sometimes you notice glitches in Firefox related to graphics card driver incompatibilities. To rule that out, you could disable hardware graphics acceleration. You usually need to restart Firefox in order for this to take effect, so save all work first (e.g., mail you are composing, online documents you're editing, etc.).
orange Firefox button ''or'' classic Tools menu > Options > Advanced
On the "General" mini-tab, uncheck the box for "Use hardware acceleration when available"
After restarting Firefox, do you notice any difference?

System.log fills up with bad packets errors (Multicast packet - CRC error)

Hello,
I've been trying to Google my problem but found no answers; hopefully someone can help me?
Whenever I'm online, my System.logs fills up (every second, and sometimes, multiple times each second) with the following message :
19/12/07 12:51:01 PM kernel AppleYukon2 - bad packet received. length: 60, packet status bits: Multicast packet, CRC error
19/12/07 12:51:01 PM kernel AppleYukon2 - bad packet received. length: 60, packet status bits: Multicast packet, CRC error
My DSL modem is connect directly into my iMac. It's a Speedstream 5360). I never have any problems connecting to the Internet and the speed I get is fine. When I configured my Network settings, I only added my PPPoE Service name username and âssword - everything else was automatically added (Ethernet configuration).
Is there anything I should change in the Advanced Settings?
The System.log causes me problem because it often causes the application Console to crash when I try to view it.

I should add that this problem didn't exist when I was using Tiger.
Also, when I called Apple Tech Support, I was simply told "just don't play with the Console".

Drop multicast packets at layer 2 or 3 ??

In one of packet tracer activity in the book "network fundamentals", it said that devices that are not configured to receive multicast traffic will drop packet at Layer 3. However, in the book "routing protocols and concepts", it said differently. It said " In addition, multicasting updates require less processing by devices that are not RIP enabled. Under RIPv2, any device that is not configured for RIP will discard the frame at the data link layer " (it means Layer 2).
Can anyone help me to explain this? Thank you very much.

Hi,
I would keep the TOR switches (3000) as layer-2 only. Create the SVIs for all your vlans on the 9396 and do the inter-vlan there. This keep your design pretty simple.
HTH

Monitor multicast packet or IP addresses

Folks:
I have just started learning and researching the capabilities of EEM and TCL scripts; however, I am still lost, yet I have a special need for a script that will - monitor packets from a few specific multicast IP addressses, and if the stream stops, send out an email or notify me somehow. Now, I am not sure if that can be done, or if it would be best to create some sort of script.
I just need to be pointed into the right direction, or just to have someone else to brainstorm with.
Thank you
JJ

Fairly certain that packet tracer does not support Secondary IP Addresses on an Interface.
Although packet tracer is great as a learning tool, it has quite a few features which are not included. If you are studying for a CCNA then investing in a cheap second hand 2950 Layer 2 switch is a god idea also.

Multicast packets per second

Are there any pointers to multicast performance numbers on a cisco switch?

Hi,
For Layer 2 platforms, IGMP snooping is implemented in hardware, so forwarding performance is only limited by the overall performance of the switch. Unconstrained multicast are forwarded as broadcasts, so the same restriction applies.
2950 specs:
http://www.cisco.com/en/US/products/hw/switches/ps628/products_data_sheet09186a00801cfb64.html
Couldn't find any specs for the 3500Xl switches, as they are well past end of sale, but they'll operate the same, with the exception that they use CGMP rather than IGMP snooping.
For the 4000, i'll need to know which supervisor, and if you are talking about layer 2 multicast or multicast routing.
HTH,
Bobby
*Please rate helpful posts.

Flood Unregistered Multicast on Catalyst 1912

Will flood unregistered multicast work on Catalyst 1912 trunk ports? Will it work for all VLANs in this port?

Yes, the Catalyst 1912 will flood all unregsitered multicast packets on trunk ports and Ethernet ports.

WLC - AP Groups - Multicast - Bonjour - Apple TVv3

Good Morning
first off - Should start off by saying I have followed the Apple Bonjour deployment guide [except for interface group] portion
I have searched high and low, here and there to no avail.
http://www.cisco.com/en/US/products/hw/wireless/ps4570/products_tech_note09186a0080bb1d7c.shtml
I am aware that the bonjour gateway IOS may or may not come out in Oct/Nov 2012, which maybe my only option at this point.
Is this not working because of my AP groups setup or have I misssed something
I can only get bonjour to work if multicast - unicast mode is selected, but our network slowly grinds to a halt, so it is not an option
when I first connect to the wireless I see 1 bonjour device for about 3 minutes and then disappears.
I can not see the appletv at all with an ipad, airplay does not appear at all.
We have the following setup.
2 campuses - Campus 2 is simular setup, but WLCs higher model and ios 7.2 and clients and subnets are double
Campus 1
2 WLC 4404 ios 7.0.230.0
30 AP groups mapped to 30 Interfaces using subnets with /23 bit subnetmasks
multicast - multicast is set with multicast addresses of
controller 1 239.239.5.1 and
controller 2 239.239.5.2
multicast is enabled
IGMPsnooping as well
On Switch multicast routing is enabled
all AP group subnets and Mgmt vlans are PIM enabled dense mode
set up a trunk to ubuntu server to act as a bonjour gateway, installed avahi and vlan
mapped all AP and mgmt vlans to Ubuntu server.
avahi see the following + more
+ eth0.136 IPv6 Apple TV                                      _airplay._tcp        local
+ eth0.136 IPv4 Apple TV                                      _airplay._tcp        local
+ eth0.134 IPv6 Apple TV                                      _airplay._tcp        local
+ eth0.134 IPv4 Apple TV                                      _airplay._tcp        local
+ eth0.132 IPv6 Apple TV                                      _airplay._tcp        local
+ eth0.132 IPv4 Apple TV                                      _airplay._tcp        local
+ eth0.130 IPv6 Apple TV                                      _airplay._tcp        local
more goes on forever
+ eth0.136 IPv4 xyz Library                             Apple Home Sharing   local
show ip multicast
Multicast Routing: enabled
Multicast Multipath: disabled
Multicast Route limit: No limit
Multicast Triggered RPF check: enabled
Multicast Fallback group mode: Dense
show ip multicast interface vlan 128
Vlan128 is up, line protocol is up
Internet address is x.x.128.1/23
Multicast routing: enabled
Multicast switching: fast
Multicast packets in/out: 14671352/276693
Multicast boundary: not set
Multicast TTL threshold: 0
Multicast Tagswitching: disabled
Where do I go from here?

Thanks Yahya and Stephen
I have tried to simplify my config as much as possible.
wlc 4404
Ethernet Multicast Forwarding............... Enable
Ethernet Broadcast Forwarding............... Enable
AP Multicast/Broadcast Mode................. Multicast   Address : 239.239.5.1
IGMP snooping............................... Enabled
IGMP timeout................................ 60 seconds
IGMP Query Interval......................... 20 seconds
I have an interface created 10.x.x.x/23
I have created a new SSID APPLETV - assigned Interface
I have added the SSID to just 1 AP Group
show network multicast mgid summary
Layer2 MGID Mapping:
InterfaceName                    vlanId   MGID
2upadhoc                         136      27
Layer3 MGID Mapping:
Number of Layer3 MGIDs........................... 11
My vlan does not show up here.
I only have 2 devices in this vlan the AppleTV and IPAD
checking the switch for all required vlans
show ip multicast
Multicast Routing: enabled
Multicast Multipath: disabled
Multicast Route limit: No limit
Multicast Triggered RPF check: enabled
Multicast Fallback group mode: Dense
admin interface
Management, AP-Manger
Vlan12 is up, line protocol is up
Internet address is x.x.x.1/24
Multicast routing: enabled
Multicast switching: fast
Multicast packets in/out: 238489978/724352
Multicast boundary: not set
Multicast TTL threshold: 0
Multicast Tagswitching: disabled
AP vlan
Vlan222 is up, line protocol is up
Internet address is x.y.z.1/24
Multicast routing: enabled
Multicast switching: fast
Multicast packets in/out: 11423/238338583
Multicast boundary: not set
Multicast TTL threshold: 0
Multicast Tagswitching: disabled
The test Apple TV Vlan
Vlan136 is up, line protocol is up
Internet address is x.xx.1/23
Multicast routing: enabled
Multicast switching: fast
Multicast packets in/out: 156740/0
Multicast boundary: not set
Multicast TTL threshold: 0
Multicast Tagswitching: disabled
interface Vlan12
ip pim dense-mode
interface Vlan222
ip pim dense-mode
interface Vlan136
ip pim dense-mode
Show ip igmp groups
Group Address    Interface                Uptime    Expires   Last Reporter
224.0.1.39       Vlan136                  2d00h     00:02:35 x.x.x.1
So just to recap
Same subnet in a AP Group
New SSID
multicast enabled on WLC - using multicast multicast mode
Broadcast forward enable
Switch -Multicast routing enabled
all vlans enabled for PIM
2 devices - added Imac to see if I could home share through Itunes.
end result
no bonjour clients, no apple tv, no airplay
Bonjour Gateway device - although same subnet it shouldn't be needed
eth0.12   Link encap:Ethernet HWaddr bc:30:5b:x:x:x
          inet addr:x.x.x.244 Bcast:x.x.x.255 Mask:255.255.255.0
          inet6 addr: fe80::be30:5bff:fed6:a178/64 Scope:Link
          UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
          RX packets:55005 errors:0 dropped:115 overruns:0 frame:0
          TX packets:23003 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:0
          RX bytes:2776156 (2.7 MB) TX bytes:11285256 (11.2 MB)
eth0.136 Link encap:Ethernet HWaddr bc:30:5b:x:x:x
          inet addr:x.x.x.9 Bcast:x.x.x.255 Mask:255.255.254.0
          inet6 addr: fe80::be30:5bff:fed6:a178/64 Scope:Link
          UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
          RX packets:42167 errors:0 dropped:115 overruns:0 frame:0
          TX packets:22340 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:0
          RX bytes:3251242 (3.2 MB) TX bytes:10373581 (10.3 MB)
eth0.222 Link encap:Ethernet HWaddr bc:30:5b:xx:xx:xx
          inet addr:x.x.x.9 Bcast:x.x.x.255 Mask:255.255.255.0
          inet6 addr: fe80::be30:5bff:fed6:a178/64 Scope:Link
          UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
          RX packets:152397 errors:0 dropped:115 overruns:0 frame:0
          TX packets:23768 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:0
          RX bytes:12795709 (12.7 MB) TX bytes:11318103 (11.3 MB)
+ eth0.222 IPv6 67665ACD317A45B0                              _appletv-v2._tcp     local
+ eth0.222 IPv4 67665ACD317A45B0                              _appletv-v2._tcp     local
+ eth0.136 IPv6 67665ACD317A45B0                              _appletv-v2._tcp     local
+ eth0.136 IPv4 67665ACD317A45B0                              _appletv-v2._tcp     local
+ eth0.12 IPv6 67665ACD317A45B0                              _appletv-v2._tcp     local
+ eth0.12 IPv4 67665ACD317A45B0                              _appletv-v2._tcp     local
Should Bonjour work same subnet with these settings?
I am going to have read more about the Interface groups and the Multicast vlan.

RSPAN does not put IPv6 multicast traffic into port

Hi.
There is two switches in the equation:
WS-C2960-24TT-L 12.2(55)SE5 C2960-LANBASEK9-M
and stack of
Switch Ports Model SW Version SW Image
1 12 WS-C3750G-12S 12.2(55)SE8 C3750-IPSERVICESK9-M
2 12 WS-C3750G-12S 12.2(55)SE8 C3750-IPSERVICESK9-M
* 3 24 WS-C3750G-24T 12.2(55)SE8 C3750-IPSERVICESK9-M
3 is a master
There is VTP domain with pruning off and RSPAN VLAN 1001
core#sho vlan remote-span
Remote SPAN VLANs
1001
there is RSPAN session on first:
#sho monitor session 1
Session 1
Type : Remote Source Session
Source Ports :
Both : Fa0/11
Dest RSPAN VLAN : 1001
Port Fa0/11 is in access mode, VLAN 303
and on second:
core#sho monitor session 1
Session 1
Type : Remote Destination Session
Source RSPAN VLAN : 1001
Destination Ports : Gi3/0/2
Encapsulation : Native
Ingress : Disabled
Problem is that i can't see any IPv6 multicast traffic (like ICMPv6 RA or such) on Gi3/0/2 which is absolutely sure there, because if i remove monitoring session on core switch and put Gi3/0/2 into trunk mode, i can see packets i need in vlan 1001:
# tcpdump -s0 -nnvei eth1 vlan 1001 and ip6
tcpdump: WARNING: eth1: no IPv4 address assigned
tcpdump: listening on eth1, link-type EN10MB (Ethernet), capture size 65535 bytes
14:17:37.059045 50:57:a8:f0:72:1b > 33:33:ff:00:00:01, ethertype 802.1Q (0x8100), length 90: vlan 1001, p 0, ethertype IPv6, (class 0xe0, hlim 255, next-header ICMPv6 (58) payload length: 32) 2abc:abc:1:600b::2 > ff02::1:ff00:1: [icmp6 sum ok] ICMP6, neighbor solicitation, length 32, who has 2abc:abc:1:600b::1
source link-address option (1), length 8 (1): 50:57:a8:f0:72:1b
14:17:38.083266 50:57:a8:f0:72:1b > 33:33:ff:00:00:01, ethertype 802.1Q (0x8100), length 90: vlan 1001, p 0, ethertype IPv6, (class 0xe0, hlim 255, next-header ICMPv6 (58) payload length: 32) 2abc:abc:1:600b::2 > ff02::1:ff00:1: [icmp6 sum ok] ICMP6, neighbor solicitation, length 32, who has 2abc:abc:1:600b::1
source link-address option (1), length 8 (1): 50:57:a8:f0:72:1b
14:17:39.107068 50:57:a8:f0:72:1b > 33:33:ff:00:00:01, ethertype 802.1Q (0x8100), length 90: vlan 1001, p 0, ethertype IPv6, (class 0xe0, hlim 255, next-header ICMPv6 (58) payload length: 32) 2abc:abc:1:600b::2 > ff02::1:ff00:1: [icmp6 sum ok] ICMP6, neighbor solicitation, length 32, who has 2abc:abc:1:600b::1
source link-address option (1), length 8 (1): 50:57:a8:f0:72:1b
There is no such problem with usual unicast and broadcast traffic.
Any suggestions?

Interestingly, i've found bug CSCsr64007 which i stubmbled upon on one of my switches during troubleshooting. The effect of this bug was that RSPAN took IPv6 multicast packets from unrelated VLANs and forwarded them into monitor port.
Looks like they have "fixed" it filtering IPv6 multicast completely.

SG300-28P Multicast (IGMP) and IGMP routing..

A brief background on the setup:
I recently switched out my switch. It was a Cisco 3750 10/100 switch and I wanted to upgrade to Gig. The cost of a Gig+POE 3750 is too much to bite so I opted for the SG300. My router is a Cisco 891. Here is the setup:
Cisco 891:
two SVI's: vlan1 and vlan 100
Vlan1 = 10.0.1.1/24
Vlan100 = 10.0.100.2/24
Connected to SG300 via Fa0
DHCP Server for vlan1+vlan100
Cisco SG300-28P:
two SVI's: vlan 1 and vlan 100
vlan 1 = 10.0.1.21/24
vlan 100 = 10.0.100.1/24
Connected to 891 on via Gi18
The connection between 891 and SG300 = trunk, vlan1-u, vlan100-t
The problem:
With the 891+3750, I was able to add "ip pim sparse-dense-mode" on all the SVI's and hosts could join any multicast group, irregardless of which vlan the host was a member of.
Now I've changed switches, and I dont get the same love. I have the PIM statement on both SVI's on the 891, but Im unsure of what I need to configure on the SG300. I have enabled "Bridge multicast filtering" + "IGMP snooping". What can I do to get similar functionality using the SG300 + 891? I assume this is my lack of understanding IGMP in general, but was able to get away with it using the PIM statements on the 891+3750 stack.
Jeff

You should be able to filter unregisted multicast on every port.
To be able to pass multicast over subnets two things must be certain, the node/device is able to send and receive multicast packets but also register the multicast address being listened to by the node so the local and remote routers can route the multicast packets.
When the switch learns a multicast address through IGMP snooping, this is a registered multicast. The switch will only forward multicast to ports that are registered to the multicast group. Where unregistered multicast comes in, is the multicast that is not statically defined or learned through IGMP which in turn will be forwarded to all ports of the vlan.

HREAP and Multicast traffic

I have a controller sat on a network (10.10.10.0/24) with a management address of 10.10.10.250. There's a distant site we have at the other side of the network with a range at 192.168.0.0/24. I have 5 thin HREAP access points on this network with three WLANs from the controller and one WLAN delivered via a trunk point with VLAN 2 tagging (the 192.168.0.0/24 network is VLAN1). The VLAN2 (e.g. 172.16.0.0/24) network is basically an untrusted network to us , but I didn't think this would matter as the HREAP config would mean that none of this traffic should even leave the access point - apart from stats/client info.
However, i've recently been seeing something odd in that there must be some multicast-talking clients on this untrusted network and whatever they are talking about I can see on my management LAN (10.10.10.0). I can basically see multicast packets with source IPs from the untrusted network. How is this possible? More importantly how can I stop it?
All network numbers are just examples. Any help or ideas would be gratefully received.

Hi Stuart,
Just to clarify a point:
"but I didn't think this would matter as the HREAP config would mean that none of this traffic should even leave the access point"
Keep in mind that when an ap is hreap mode, the ap essentially acts like a switch with respect to its ethernet port. When it gets a packet from the wireless side, if appropriate, it tags it and puts it on the wire.
Under ordinary circumstances (unless something is configured to stop this), if a wireless client connected to an hreap ap sends a multicast packet, it absoutely will be put on the wire by the ap, just as a broadcast would. I just confirmed this with lab equipment.
So if there isn't a routed path from the remote untrusted networks to your mgmt vlan, there may (should) be L3 multicast routing configured for the untrusted and your management routed interfaces. Is this the case?
thanks
Jeff

WRT120N wireless nodes not routed to WAN, Multicast not working

Hi. Since a few weeks, I am experiencing strange and very annoying problems with my WRT120N. I have a DSL connection at home and the router connects to that via PPPoE. The LAN consists of one wired node and several wireless nodes. I have a G/N mixed setup because I also have G-only nodes (older laptop, mobile phone).
Every few minutes, my wireless nodes are not routed to the WAN anymore. Weird thing is: they can still connect to the wired node on the LAN so bridging seems to work fine. They can also connect to the router itself and the router says it is connected to the WAN. I can confirm this WAN connection because the wired node is being routed to the internet all the time. Restarting the router solves the problem. Actually, even if just disabling/enabling the wireless connection on my nodes solves it. However after a few minutes, sometimes seconds, routing stops working again (It happened twice during the writing of this email).
Another thing that is really bugging me is that multicast seems to get filtered. After a few minutes, no multicast message is being sent to the wireless nodes. Multicast packets sent by the wireless nodes do arrive at the wired node but any answer is being filtered on the router.
I have changed pretty much every possible setting that could be connected to the issue but no improvement (e.g. filtering multicast in the firewall). I used to be on 1.0.0.4 and hoped that upgrading to 1.0.0.5 would help but it didn't. I also checked this forum for solutions but found none that is working for me. This way, the router is pretty much useless for wireless clients as after an arbitrary but pretty short time interval they can only connect to the LAN and no Multicast service discovery/media streaming is possible. I really need help on these issues.

Hi Brickmonkey,
thanks a lot for your answer. I did the changes you advised. In fact, here's in detail what I did:
Router reset as described.
Changed the following configuration options:
PPPoE + Credentials
Local IP
MAC-IP Bindings for DHCP
Time Zone
DynDNS
Wireless Mode -> Mixed
SSID
Channel Width -> Auto
Wireless Security -> Enabled
Encryption AES
Passphrase
Port Forwarding for SSH,HTTPS
Router Password
Changed the options beacon interval, RTS threshold, fragmentation threshold and MTU as advised.
Router power cycled.
Routing and multicast are running since 5 minutes. Let's see if it lasts.
Answering your question: I do have one wired machine directly connected to the internal switch at the WRT120N. That's the one the ports are forwarded to. It has a static IP outside the DHCP range and is actually my DHCP,DNS etc server - however DHCP is disabled at the moment. All my other machines are wireless clients with G or N connectivity.
Can you explain the reason behind your proposed configuration changes?

Multicast blocking in layer 2 switch

Hello there,
I need your help, this is the problem that I have.
We have a 3750X with 7 ports assigned to a different multicast IP address (connected to the encoders), these are the ports with the multicast ip address and the rate that the encoder is sending:
Pto 2 - 230.1.1.1:5001 - 3.5 Mbps
Pto 3 - 230.1.1.2:5002 - 3.5 Mbps
Pto 13 - 230.1.1.22:5022 - 15 Mbps
Pto 13 - 230.1.1.23:5023 - 15 Mbps
Pto 13 - 230.1.1.24:5004 - 15 Mbps
Pto 13 - 230.1.1.25:5025 - 15 Mbps
Pto 13 - 230.1.1.26:5026 - 5.0 Mbps
The last port (48) is connected to a different device and this box is receiving the multicast ip addresses. My problem is that in every single port on the switch is receiving all the multicast traffic so the switch is having high cpu, I have the outputs from the console monitor (application that sees the odd behavior).
As far as I know this is expected since this is layer 2 device but I'm not sure. Please help so I can configure what I need to stop the high cpu and the traffic to be sent over the rest of the ports (including those ports).
Kindly regards

Hi ,
You can block layer 2 Multicast traffic with following commands
Step 3
switchport block multicast
Block unknown multicast forwarding out of the port.
Note Only pure Layer 2 multicast traffic is blocked. Multicast packets that contain IPv4 or IPv6 information in the header are not blocked.
http://www.cisco.com/c/en/us/td/docs/switches/lan/catalyst2960/software/release/12-2_55_se/configuration/guide/scg_2960/swtrafc.html
HTH
Sandy

Socket.receive not picking up large packets

I have found that the socket.receive method on some systems has trouble picking up large multicast packets from the network (i.e. 50k). Running ethereal, the packets are making it to the machine but the receive method continues to block as if nothing was there. It seems to be an issue with redhat linux since the software I have been told works fine on a windows machine. I am currently running the software on core 2 and I believe we are experiencing a similiar problem on redhat 9. Has anyone experienced this problem before and possibly know how to fix it? Any suggestions would be greatly appreciated. Thank You.

No answer for you, I'm afraid, but some possibly illuminatory questions.
Are you able to determine the boundary between the sizes of packets that can be received and those that can't? Is the boundary precise, or fuzzy (ie, do packets get lost intermittently when sizes are near the boundary) ?
Are you running firewalling software (iptables?) on your LInux system?
Is your Linux system configured always to defragment packets prior to firewalling? If so, if you reconfigure it not to, does it start working?
Does it work if the packets are simply broadcast rather than multicast?

Multicast packets on trunks

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