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Multicast Question

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Ryan_G
Frequent Advisor

Multicast Question

Hi All

Im trying to use a classroom Management tool called ABTutor here. I have a network setup where staff and students are segregated (different vlans) and for the tool to work need to use multicasting.

I'm not an expert on this. I thought all i would need to do is setup multicasting on each vlan (on the core 5400 switch). using ip igmp command.

is there anything else i need to do?
do i need to set this command on all switches on the network (or just the core as it is doing the routing)?

Thanks in advance.
15 REPLIES
Ryan_G
Frequent Advisor

Re: Multicast Question

A bit more info.

Multicast: This method sends a multicast message on port 5151 to the networks multicast address. Multicast messages can traverse across subnet (see Subnets to Scan), but you must make sure the routers allow multicasting. This is especially important for Wireless routers as most have multicast turned off by default.


Now with this in mind. I would of thought i would have to forward the protocol on port 5151, However, I do not have a single source IP address. Can I just allow any IP address to broadcast on 5151?

Thanks
Matt Hobbs
Honored Contributor

Re: Multicast Question

Generally for multicast to traverse VLANs you need to enable ip multicast-routing globally, IGMP on each VLAN, and then enable PIM on those VLANs.

For PIM support you need the Premium Edge License installed.

Ryan_G
Frequent Advisor

Re: Multicast Question

Thanks Matt.

Not what I wanted to hear about having to be the Premium Edge License.

You said you have to enable multcast globally? How do you do this? I dont see anything obvious.... That doesnt mean it doesnt exist.
Matt Hobbs
Honored Contributor

Re: Multicast Question

Hi Ryan,

To enable multicast routing (you'll kick yourself):

ProCurve Switch 5412zl(config)# ip multicast-routing

I'm looking at the doco for this application though and I'm not quite sure how it works with multicast, it's not clear at all. I'm wondering if it actually uses directed broadcasts instead to reach clients across VLANs.

To enable directed broadcasts:

ProCurve Switch 5412zl(config)# ip directed-broadcast

If that doesn't help, I would be interested in seeing a packet capture filtering UDP port 5151. You might be able to get this working without having to purchase the premium edge license if we can understand exactly how it works.

Ryan_G
Frequent Advisor

Re: Multicast Question

I assumed it would be that obvious too... BUT


ATCGC-Core1(config)# ip multicast-routing
Invalid input: multicast-routing



ATCGC-Core1(config)# show version
Image stamp: /sw/code/build/btm(t2a)
May 29 2007 16:54:17
K.12.16
159
Boot Image: primary

ATCGC-Core1(config)# ip
access-list Enter the named-acl context for the specified access
control list.
arp-age Modify Address Resolution Protocol (ARP) table entry
timeout, specified in minutes.
authorized-managers Define the stations allowed to manage the switch.
default-gateway Configure the Layer 2 default gateway address, which
will be used when routing is not enabled on the switch.
directed-broadcast Enable/disable directed broadcast forwarding.
dns Configure the DNS (Domain Name System) default domain
suffix and the name server IP address for translation of
host names to IP addresses.
icmp Configure ICMP Rate Limiting capacity.
irdp Enable/disable ICMP Router Discovery Protocol (IRDP).
load-sharing Specify the maximum number of equal cost IP load sharing
paths.
route Add or delete static routing table entries.
routing Enable/disable IP routing support on the device.
source-binding Add/remove a static IP-to-MAC binding in the DHCP
snooping database.
source-route Enable/disable forwarding of source routed packets.
ssh Enable/disable SSH server on the device or set various
SSH server parameters.
timep Configure the method to acquire the Timep server
address.
ttl Specify TTL for outgoing IP packets.
udp-bcast-forward Enable/disable UDP broadcast forwarding.
zero-broadcast Enable/disable usage of zero broadcast IP Address.

Its not as listed command....

Any ideas?
Matt Hobbs
Honored Contributor

Re: Multicast Question

Okay, guess you do need to premium edge license to even enable it.

Don't worry about that for now, see if the directed-broadcast helps and see if you can get a packet capture to understand how this app actually works.
Matt Hobbs
Honored Contributor

Re: Multicast Question

You might also be able to use the UDP Broadcast forwarding feature (ip forward-protocol), check out the Multicast & Routing guide.

I've got a very good feeling that might just do the job.

Ryan_G
Frequent Advisor

Re: Multicast Question

The only thing with the ip forward-protocol is that I dont have a static address (or UDP server) that it is being sent from. Unless there is a way to forward any port without using a server address then it doesnt work.

The 'master' machines are laptops which will change from every room every session.

Or Am i reading it wrong?
Ryan_G
Frequent Advisor

Re: Multicast Question

I can also rule out the directed-broadcast as the software in question doesn't support it, only multicast.
Ryan_G
Frequent Advisor

Re: Multicast Question

Have Uploaded 2 wireshark captures (I didnt know how to export them as text).

One is ABtutor working as a broadcast, and One is it working as a multicast.

Thankd again Matt, your a champion.
Ryan_G
Frequent Advisor

Re: Multicast Question

This is multicast Capture. COuld only upload one attachment at a time.
Matt Hobbs
Honored Contributor
Solution

Re: Multicast Question

Yep, the udp forward-protocol listens for broadcasts on a given VLAN and then forwards it other VLANs. What you can do is set it to forward to an entire VLAN by using the broadcast address on that other VLAN.

So Master laptop on VLAN 1 - 10.0.1.1/24
Clients on VLAN 2 - 10.0.2.1/24
Clients on VLAN 3 - 10.0.3.1/24

conf
ip udp-bcast-forward
vlan 1
ip forward-protocol udp 10.0.2.255 5151
ip forward-protocol udp 10.0.3.255 5151


In the next classroom, Master laptop on VLAN 2:

Clients on VLAN 1 - 10.0.1.1/24
Master laptop on VLAN 2 - 10.0.2.1/24
Clients on VLAN 3 - 10.0.3.1/24

conf
vlan 2
ip forward-protocol udp 10.0.1.255 5151
ip forward-protocol udp 10.0.3.255 5151

I'd then try using the standard broadcast option in the application (not the multicast).


Matt Hobbs
Honored Contributor

Re: Multicast Question

Thanks for the captures. I'm confident that using the udp forward-protocol using the broadcast method those packets will reach the clients. What I'm not sure of is how the clients send return traffic back to the Master.

I can also see in the second capture that it is definitely using multicast, so really you would need the premium edge license to route that if the first method doesn't work out.

If you have a 5300 somewhere you may be able to get that to be your multicast router (comes included) on the same network, but would need some creative thinking to get them to coexist.
Ryan_G
Frequent Advisor

Re: Multicast Question

your a legend matt. I owe you about a carton by now....

The udp broadcast-forward did the trick.
Matt Hobbs
Honored Contributor

Re: Multicast Question

Always a pleasure. I saved you about 100 cartons worth alone on that premium edge license! I'll never make a good salesman.

Just glad to see you're making the most out of your original investment there. It's great to see the benefits you get with ProCurve, new features coming out for free all the time that often come in very handy down the track.

I'm sure that when you do need any upgrades to your network you'll know which vendor to stick with. That's worth more than a few premium edge licenses to HP.