Multicasting and loopback

[Shirley Barger]

We run Oracle Application Server 4.0.8.2 on an L-1000. The L is our only OAS node. OAS by default uses multicasting--you can't opt out even on a single node. However, an Oracle doc on multicasting/OAS says you can "bind the multicasting to the loopback device so there is no impact on the local network." They say to add a route so that 224.0.0.0 traffic is routed to lo0. I'm not finding any docs on doing this on HP, and I'm not comfortable experimenting on this box (OAS is fragile). Can this be done? If so, what should the "add route" command look like? Thanks very much.

[Sridhar Bhaskarla]

The loopback address is 127.0.0.1. Did you try adding the route through this address?.I am not sure if it works.. but an idea.

-Sri

[Scott Van Kalken]

route add is the command you want.

Not 100% sure how to use with multicast - however the man page on the route command should tell you.

I've not used for multicast, only for simple routes.

Although, we route a client network back via one of our boxes. Well, one IP address at least.

Scott.

[Anthony deRito]

Hi Shirley, well the concept makes sense to me... forward all packets destined to the base multicast address to the loopback address of the interface card where they would be dropped. However, you said that this is your only OAS node on your network. If this is the only node, what device would receive the multicast? There has to be some form of multicast grouping set up at the application level and I would presume it would have been done during the time of OAS installation on another node. In other words, other nodes must be "tuned" into this multicast address.
That the whole idea of multicasting... to transmit data to more than one machine at a time.

According to MetaLink, on a single node install of OAS, it can be possible to bind the multicasting to the loopback device so there is no impact on the local network. On Solaris for example:

(a) Ensure your loopback device has been defined and accepts multicast traffic. For example, if your loopback device is lo0, use
the equivalent of "ifconfig lo0" on Solaris and grep for MULTICAST.

# ifconfig lo0 | grep MULTICAST

lo0: flags=849 mtu 8232

(b) Add a route so that 224.0.0.0 traffic network is routed to the lo0 (or your defined) loopback device.

(c) Edit your resources.ora file and add the following line:

zyg.network = 127.0.0.1


Hope this helps!

Tony

[Shirley Barger]

Thanks, but we had tried a few variations of "route add" on Monday, and the result was:
add net 224.0.0.0: gateway 127.0.0.1: Network is unreachable
Also, if we weren't encountering that problem, we also were not sure what the value of netmask should be. I should have mentioned that we'd tried a "route add" lines that failed, but that also meant we'd done no damage to make OAS blow up.

Anthony, I'm afraid you quoted from the same document I quoted from in my initial mailing, so I know the doc already. Early on, it explains that, "Because a single-node installation is just a special case of a multinode installation ... it is easier to have it use multicasting to communicate between the various components of OAS on that machine." In other words, Oracle built it this way, that's it. There was *no choice* during installation as to whether one would have multicasting. What they do offer is this doc which says you can bind the multicasting to loopback, but I'm just not knowledgeable on how to do this, and I'm afraid of mucking up. Making seemingly simple changes in the environment or OAS configuration before has been painful.
Thanks!

[Anthony deRito]

Hi SHirley, did you try posting this question on the MetaLink Oracle forum? I am sure there is some DBA out there thats using OAS and has the same problem/issue. Also, I don't blame you for not wanting to muck things up... does this mean you don't have a test/developement server to try things out on? Even when you do finally find the answer, your probably not going to want to put the change in a somewhat high risk box.

Sorry to not help you further.

Tony