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Apple Time Capsule, more than you wanted to know!

Started by bicknell, January 27, 2012, 11:21:40 AM

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I set up an Apple Time Capsule recently and I'm very pleased with the results.  The unit I set up is a 4th Gen, and is likely the same (with the addition of a hard drive) as the Apple Extreme Base Station.  It's running software version 7.6.

Instructions to set them up for IPv6 are readily available (TunnelBroker will tell you how!), so no need to rehash that set of steps.  The issue I found was with monitoring, no one had documented how the various interfaces were set up.  I did some trial and error, and figuring it out.  Attached to this post is a block diagram of the architecture of one of these boxes.  There are 11 interfaces exposed to SNMP:

mgi0 is the WAN.

mgi1 is connected to an internal 4 port GigE switch that appears to not have any individual pollable ports via SNMP.  The other three ports are exposed on the back of the unit as the LAN ports.

wlan0/wlan1 are the data connections for the 2.4Ghz and 5Ghz radios, respectively.

bwl0/bwl1 appear to be some sort of managmenet interface for the radios.  They report outbound traffic only, never inbound.  Traffic on these interfaces increases as traffic increases on the wlan0/wlan1 interfaces, but at a much lower rate.

bridge0 is a software bridge that sits between wlan0, wlan1, and mgi1 briding the WiFi's and LAN ports together.  Traffic between any two of these three will pass the bridge interface.

pppoe0 is for tunneling PPP over Ethernet, if you use that on the WAN port, basically in that case mgi0 would be with PPPoE overhead, and pppoe0 would be without.

gif0 is 6in4 tunneling, if you have for instance a tunnel broker tunnel.  Again, this would be traffic with no overhead, then as the packets go out mgi0 they would count there with the tunnel overhead.

sth0 is 6to4 (automatic) tunneling.  Again, this would be traffic with no overhead, then as the packets go out mgi0 they would count there with the tunnel overhead.

lo0 is the loopback, not shown in the diagram.

Lastly, there's a SATA port to the disk in a Time Capsule.

I ran the ICSI Netalyzer (http://netalyzr.icsi.berkeley.edu/) against it (with an HE tunnel configured for IPv6 connectivity) and it basically passed with flying colors.  There are the following minor notes:

  • For some reason the DNS server in the box won't pass TXT records over 1500 bytes.  It has no trouble with other large DNS records, which is odd.  Probably most users would never notice.
  • The built in NAT handles FTP in a way that generates a warning, but will probably work for most people.  It only applies to Active FTP, passive mode is your friend.
  • An IPv6 MTU issue appears.  I don't yet know if this is the fault of the Time Capsule or the result of HE's tunnel config.  I have a separate thread in another forum where I am trying to track that down.
  • In SNMP it reports all the GigE interfaces are 10Mbps.  This makes tools like the MRTG cfg maker generate bad configs.  Manually setting the config to GigE makes for pretty graphs.
  • It only supports SNMPv2c for mgi0 and mgi1!  If you want to monitor the other ports you have to use SNMPv1.  I decided to use v1 for everything and monitor at 1 minute intervals to prevent counter wrap.
  • It's missing two features I think some users would like to see, it doesn't act as an NTP server for your LAN, and it doesn't support UPnP since apple is a NAT-PMP shop.  If you have Mac clients they will probably prefer the NAT-PMP behavior, but if you have other clients the lack of UPnP may be mildly annoying.
Otherwise it passes with a perfect grade, including an impressive performance of not showing any buffer bloat!  Throughput is awesome, I was able to get 500Mbps (yes, half a gig) reading and writing the internal disk from a wired-connected machine.  I've spoken with an Apple engineer before who told me it can easily route and tunnel a full GigE, alas I have no way to test that with this current unit.

Overall, two thumbs up!

Anyway, just leaving this here in case other people are looking for the SNMP info or general feedback.