Multicast IP for clustering

[mohdamir]

Dear Gurus,
We want to test our Oracle Application Server clustering, can we have a multicast for IP address? Let say IP for server A is 10.1.63.94 and IP for server B is 10.1.63.95.What's the best method to do the multicast IP? Can we configure the same virtual ip for both servers?

TQ

[Duncan Edmonstone]

I don't know much about multicasting, but you certainly shouldn't be configuring the same virtual IP address (i.e. ifconfig) on both servers - that breaks standard IP rules. As I understand it servers don't actually have multicast IP addresses bound to physical interfaces - rather they "join" multicast groups (this is handled I think by your application, not through anything you have to do in HP-UX). If these systems talk and multicast out of the same interface that you have your default route assigned out of, I don't think there's anything to do. If the multicasting needs to be out of another interface, you'll need to add a route to your routing table to point multicast traffic out that interface.

See the following manual for a little more detail:

http://docs.hp.com/en/B2355-90796/ch06s10.html

and if you have multicast traffic that needs to leave your local subnet, then potentially you'll need to configure the multicast routing daemon (mrouted) - which I'm afraid is beyond my understanding...

Don't know if that really helps, but you now know as much about multicasting as I do!

Duncan

[Matti_Kurkela]

Multicast addresses are in the range 224.0.0.0 - 239.255.255.255, and they do not follow the same rules as standard IP addresses. Some multicast addresses beginning with 224.0.0.* and 224.0.1.* are reserved for specific purposes: you should avoid using those in your cluster.

The main network protocols used with IP multicasting are UDP and IGMP; TCP cannot be used at all.

A multicast IP address is a _multicast group identifier_: it is not a virtual IP. A multicast IP should never appear as a source address: it is used as a destination address only. You should never use SAM or ifconfig to set the IP address of a network interface to a multicast address: it simply does not work that way.

In your situation, the multicast address is configured in the OAS settings only, and all OAS nodes in the same cluster must have the *same* multicast IP address, otherwise they cannot send multicasts to each other.

When the OAS cluster is starting up, OAS will request the OS to start receiving multicast messages belonging to the multicast group identified by the multicast IP address. HP-UX will then automatically send an IGMP message to the network.

As your OAS servers have consecutive IP addresses, they are most likely located in the same IP network segment. So you don't need to use mrouted.

If your server has only one configured network interface, you may not need to do any OS configuration at all. If you have multiple configured network interfaces, you may have to set up a special multicast route to identify which interface shall be used to send out the multicast messages. See this document:

http://www.docs.hp.com/en/B2355-90796/ch06s10.html

Note that the "gateway" address of a multicast route is the address of the chosen network interface in the same host. This is why the route count value is set to 0 on a multicast route.

Your network switch(es) must support multicasting. The lowest level of support makes the switch treat multicasts the same as broadcasts, which is not ideal: in this mode, the switch will send the multicast messages to all ports in the network segment, which wastes network bandwidth.

If your switch has a feature called "IGMP snooping", enable it. This makes the switch detect which servers belong to which multicast groups, and will send the multicast packets to only those servers that have requested to receive them.

If your server A is connected to one switch and server B to another, you must make sure that the link between the switches is configured to relay the multicast information between the switches. This may be manufacturer-specific: see the documentation of your switches.

MK

[Taifur]

Hi MOhdamir

You can check below link for IP multicast as follows,

http://docs.hp.com/en/B2355-90796/ch06s10.html

Rgds//
Taifur