mulitcasting issues

[craymond]

is it true that multicasting only works on the local subnet? In the retrospect configuration, it gives you a place to input the number of router hops so that seems to indicate that it is indeed capable of mulitcasting across subnets.

 

We have a retrospect server on 1 net & backup clients on mulitple nets. We'd like to use multicasting to back them up. The reason for this is that we are using DHCP & don't want to use the direct access method that would require inputting a static ip for every client.

 

 

 

Do you have a list of multicast specifications? I noticed that retrospect has its own multicast group address of 224.1.0.38. Any info you have on multicasting/multicast configuration would be much appreciated. I haven't found much in the documentation.

[IrenaS]

By definition, Multicast works within the local subnet only. Sending out a broadcast to other subnets (subnet broadcasting) can be done, and is pretty similar to multicast.

 

 

 

Set up subnet broadcasting to search in the subnets you want to back up from. This will allow you to search in other subnets for any Retrospect clients, and you'll be able to back them up even if the IP address changes.

 

 

 

Subnet Broadcast is not included in every version of Retrospect, though. On any Windows version or Mac 5.0, only the Server version has it. Mac 4.3 or prior has it in all versions.

 

 

 

Irena Solomon

 

Dantz Tech Support

[craymond]

thanks for your reponse but we can't do subnet broadcasting because broadcasts are blocked by the router. So short of putting a backup server on each net it looks like we're out of luck.

 

So it looks like multicasting is not an option for us, eh?

 

Can you think of any workarounds for this? We run cisco routers between subnets.

[IrenaS]

Is there a way to enable broadcasts through a certain port only? Retrospect requires incoming and outgoing TCP and UDP, and uses port 497.

 

 

 

If you cannot do this, and can't set your routers to pass this type of traffic, then the Mac product doesn't really have any other workarounds. I've seen posts on various newsgroups wherein people used ResEdit to hack Retrospect, though.

 

 

 

Retrospect for Windows actually does have the option to increase the Time to Live. Most networks do not support IGMP Multicast Packet Routing required to support a TTL greater then 1. The Subnet broadcast options solves the problem far more often for customers that need to back up over multiple subnets.

[waldorfm]

We had the same problem since we switched to a VLAN. Yes Multicast broadcast goes only to the subnet by default for reasons. However, I modified our Retrospect for Macintosh Servers with Resedit to allow it spawn Multicast over several Routers. If you have a copy of Resourcers you can open Retrospect and search for "uttl". If I remember correctly the resource to modify is called def# and there is a UTTL value of 0000001. Change it to 000006 to e.g. let it multicast over 6 hops. Works for us! You can apparently also do this in Retrospect 5 if you open the Application package contents (control-click) and modify the application.

 

 

 

I have asked for detailed multicast specifications from Dantz, in particular what the client and server are talking together, but have not received any info. Our Network Department asked for it, since we still have some trouble configuring our Routers, in respect to Multicast broadcasting.