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I need to know where in the User Guide the feature mentioned in this article is documented:








I doesn't seem to appear in the user guide for Retrospect 5.0 for the Mac that I got with the upgrade, or with the copy I just downloaded this morning.




This is mission-critical for us and without being able to change the multicast TTL we will be unable to upgrade to Retrospect 5.0 and will have to look for another backup solution. We need to back up IP clients on multiple subnets. In the past it wasn't an issue because we used AppleTalk but with Retrospect 5 we have to use IP.



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Our network is designed to not allow generic directed broadcasts across our routers. This is for security and performance issues, as we have over 1600 nodes across 22 subnets. We tried setting the router so that any packets on port 497 that try to pass through the router be forwarded to the IP address of the Retrospect user (a la DHCP relay) but that didn't work.




I found in the Windows manual that you can change the multicast TTL in the Windows version. That must be why it's listed in your knowledge base, though it doesn't say it's a Windows-only feature. So it isn't out of the question for us to ask how we can get this to work with the Mac version.

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Subnet broadcast has been deprecated by the IETF and products should not be written that depend on it. Those routers that support it are typically configured to have it turned off due to the packet explosion fun that zillions of denial-of-service scripts.




Of course, multicast routing isn't widely supported or deployed either, which makes it harder.




Basically the product should provide the choice of subnet broadcast, multicast, or port scan.

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  • 9 months later...



Mac OS 9 users can try following directions:


Yes, you can change the Macintosh version to use a TTL greater then 1.



Retrospect sees Clients on the local subnet by implementing its own name service using multicast packet forwarding, a part of IGMP (Internet Group Management Protocol). By default, Retrospect uses IP Multicast packets that have a TTL (time-to-live) of one, so they cannot cross a router. Routers decrement the TTL of a packet by one before routing it, and will not route a packet of TTL zero. To make Retrospect see Clients beyond a router, one can increase the TTL value of the name service packets in a Retrospect program resource



The router has to support IGMP multicast packet forwarding.

Setting the TTL to 2 would enable Retrospect to see across one (1) router, setting it to three (3) would make it see across two routers (2), etc. Be aware that the more routers there are to cross, the more there will be increased network traffic for all routers involved.


Do not attempt to set TTL to zero - this will prevent IP Multicast packets from leaving the backup Mac.


It's important to note that we have not tested this, and it is not guaranteed to work.


Procedure for increasing TTL within Retrospect:

Open a copy of Retrospect 4.3 or 5.0 under OS 9 in ResEdit. Open the DEF#128 resource. Scroll down to Key 26 "UTTL" and change its value from $00000001 to $00000002 for a TTL of 2, to $00000003 for a TTL of 3, and so on.


Retrospect 5.0/Mac OS X users may find that this modification will not work due to network implementations under OS X. Mac OS X customer should use the Subnet broadcast features built into Retrospect.

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Thank you for your fast response.


Using OS X and Retrospect 5 and current experience with subnet broadcast.


Configuring subnet broadcast - this does not seem to be functioning on our network; port 497 is not being filtered or blocked, clients can be pinged in other subnets, OS X firewall is off, clients in same subnet are visible (show without using direct IP connection). After configuring subnet broadcast, clients in that subnet do not show up. What questions should I be asking of my network admin?


Concerning Multicast:

It is strange that to change this (TTL) setting on the Windows version is so easy to use and configure (and it works!) and yet it is "unsupported" on the Mac OS X version 5. It is rather frustrating to see the Windows version 6 work and the Mac OS X version 5 not work.




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OK - subnet broadcast is up and running, it seems that (as stated in other posts) the Cisco router we are using by default blocks subnet broadcasts, we are currently setting it to only allow the retrospect backup server to make subnet broadcasts (yea).


My final question: which is better (uses less resources, uses less bandwidth), and what are the trade-offs between using subnet broadcast and multicast?


Another final question: when will multicast be functional on OS X?


Regarding the information provided for increasing the TTL in version 5 on OS 9 - it worked (multicast was opened up on the router between three subnets we were testing).

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  • 1 month later...

It's been a few months since I posted this...


Is there now or are there plans to include in Retrospect for OSX the ability to change the TTL count? You can do it in Windows and you can use that ResEdit hack to do it with OS 9 but it's to the point where I can no longer run Retrospect under OS 9.


I used to have some friends at Dantz that I could pressure for an answer (Craig for one) but they have left so I guess I'm at the mercy of this forum.

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There hasn't been a new Mac version since this thread was started. There is a new version about to begin beta testing now, though. One can always hope that some of the features currently in the Windows version will have finally made it into this next release.

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  • 3 months later...


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