New Time Capsule subnet mask seems to block parts of network.

Question

Level 1

8 points

New Time Capsule subnet mask seems to block parts of network.

I'm hoping Bob Timmons, La Pastenague or similar stars might chime in on this.

I replaced an apparently failed ~ 6 y.o. Airport Extreme with a 2TB Time Capsule, v. 7.7.3 earlier this week. Topology is: Cable co-ax incoming to a Cisco DPC 3925 modem/WAP/PAP2 (VoIP service). WAP is inactive. Single ethernet cable (there are 4 ports - only using one) out to TC WAN port. TC LAN ports are cabled to a) Roku, b) HTPC running Windows Media Center and c) a 16-port ethernet switch. Switch provides service to 3 WMC extenders, 1 additional Roku, and several other unused jacks around the house. With previous AP Extreme, this arrangement worked flawlessly. So well that after ~4.5 years I forgot many of the particulars, and had failed to record enough salient info. Upon installation the TC provided Wifi immediately, but I struggled somewhat with HTPC - somehow DHCP was OFF, but easily fixed. However, nothing on the other side of the switch was visible. I consulted a knowledgeable network person (but who has no Apple familiarity) and he told me that a subnet mask of 255.255.240.0, which the TC set automatically, could be putting things on different subnets, making them invisible (and un-ping-able). TC was in DHCP and NAT mode automatically. I changed the subnet to 255.255.255.0 and suddenly I was able to ping the extenders and all was well. Changing the subnet mask, however, required that I change to DHCP-Only mode then switch back, as the subnet is grayed out and not editable in DHCP-and-NAT mode. This worked in the near term, but after running some errands, the subnet mask reverted to 240 in that octet, and once again everything behind the switch was invisible and couldn't be pinged. I am using an iPad Pro v.9.3 with AirPort Utility for iOS v. 1.3.4, to interact with TC. The DHCP range is 192.168 (rather than 10.0 or 172.16), Range Beginning is 192.168.1.2 and Range Ending is 192.168.1.200. LAN IP address is 192.168.1.1. One of the extenders, e.g. is 192.168.1.100. (That would put it in the proper range, wouldn't it?) Am I mistaken in thinking that it is only a subnet mask issue? Do any port settings need to be made? I have the feeling that the fix is simple, yet clearly outside my grasp.

I appreciate all input. It's been very informative reading through the posts. Please let me know if any more info is necessary.

Time Capsule 2Tb-OTHER, iOS 9.3, AirPort Utility 1.3.4

Posted on Apr 23, 2016 6:28 AM

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Answer 1

Bob Timmons

Level 10

185,138 points

Apr 23, 2016 7:14 AM in response to LarryC60

The Cisco DPC3925 is a gateway.......a separate modem and a separate router in one package. The wireless function of the Cisco gateway might be turned off, but the device still functions as a wired router.

So, with a router already "upstream" from the TC, the TC needs to be configured to operate in Bridge Mode (Apple calls this "Off (Bridge Mode)".

As it stands now, you are trying to run two devices, both acting as routers on the network, and the TC is on a different subnet than the Cisco gateway. This creates a Double NAT error.....never a good thing....and it also prevents full communications from devices that are connected to the TC to devices connected to the Cisco gateway.

You only want one device acting as a router on a network....and the Cisco product is the one that will be performing this function.

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Answer 2

LarryC60 Author

Level 1

8 points

Apr 23, 2016 7:21 AM in response to Bob Timmons

This was one of my concerns - whether the Cisco was also providing DHCP, but wasn't sure how to verify.I did try Bridge Mode earlier, but seemed to lose everything. Will try again and report back. Thanks for the ultra-rapid reply.

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Answer 3

Bob Timmons

Level 10

185,138 points

Apr 23, 2016 7:29 AM in response to LarryC60

When you change the TC to Bridge Mode, after it restarts, power off both the Cisco and TC, wait a minute, then start the Cisco device and let it run a minute or two, then start up the TC.

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Answer 4

LarryC60 Author

Level 1

8 points

Apr 23, 2016 7:49 AM in response to LarryC60

Yes - same issue recurs: "Internet" indicator goes from green to amber/orange, and WAN connectivity to the internet is lost. (Mind you, this the AirPort Utility app on iOS, which doesn't seem to have as much "control" as with the native OS X utility. My MacBook is old and keeps warning me that the utility needs to be upgraded to work with this TC - but OS can't be upgraded far enough to handle the new utility, so Catch 22.) So, should I reset the TC and then establish Bridge Mode? I am a networking neophyte - and NOT a Wireless expert as the "badge" suggests. Have to address that! Thanks again, Bob.

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Answer 5

LarryC60 Author

Level 1

8 points

Apr 23, 2016 7:51 AM in response to Bob Timmons

Sorry. Didn't see your 2nd reply before sending my update. Will do as you suggest and update.

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Answer 6

LarryC60 Author

Level 1

8 points

Apr 23, 2016 8:31 AM in response to Bob Timmons

Bob - I receive two error msgs. "AirPort base station does not have a valid IP address", etc. & "No DNS Servers This Airport base station doesn't have any DNS server addresses" etc. Both of which I would have assumed would come from the Cisco. That puts me dead in the water. Lost everything for awhile and took awhile to restore to previous settings just to get connectivity back. Would I be better off with my own plain docsis 3.0 modem without the gateway function? That way I control DHCP completely? Even with a new VoIP provider, I'd be saving in the long run - no device rental, etc.

Larry

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Answer 7

Bob Timmons

Level 10

185,138 points

Apr 23, 2016 9:25 AM in response to LarryC60

Temporarily, disconnect the Ethernet cable from the WAN port on the AirPort Time Capsule.

Connect a computer to the same Ethernet cable as a test and see if you can get a good Internet connection that way

If you can, then so too should the AirPort. Start over and reset the AirPort back to factory default settings and let Apple's setup wizard guide you through the setup.

If you cannot get a good Internet connection during the "test", then there is a problem with the Cisco device that will need to be identified before you can proceed further.

If you have the option to use a simple modem instead of a gateway, that would simplify things quite a bit and allow the AirPort to function as the main router using DHCP and NAT for the network.

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Answer 8

LarryC60 Author

Level 1

8 points

Apr 23, 2016 11:32 AM in response to Bob Timmons

I was able to connect to internet via the WAN cable as you suggested, though needed to power cycle gateway 1st. Strangely, after restoring to factory settings, the TC has disappeared, but I have wireless connectivity and am able to see internet. AP utility does not see TC, but continues to search. TC meanwhile blinks an amber light, and I'm accessing Wifi via Apple Network 6a9cd9. Weird. So somewhat stuck right now, but will try another reset later, after running some errands, and try to regain contact with TC. Thanks for the continued help. Errands may include a trip to Best Buy for a new modem. Will reply more later.

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Answer 9

LarryC60 Author

Level 1

8 points

Apr 25, 2016 6:06 PM in response to LarryC60

Many thanks to Bob Timmons on the issue I posted Saturday. I did get a new router, an Arris SB6141. After installation and activation the remaining steps were trivial. Clearly, two devices both trying to make DHCP calls on one network is a non-starter. Thanks again, Bob.

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