rtadvd resets default gateway to link-local address in OS X 10.6.5

[jollino]

Hello,
I have been testing IPv6 on my home network and I have decided to let my iMac act as a gateway, as it's the only machine that stays on most of the day. Everything works fine with the he.net tunnel, but a few seconds after I start rtadvd, the default v6 gateway is automatically set to the link-local (fe80::/16) address of the en0 interface, breaking v6 routing for my whole network. Manually deleting such route and readding the correct one (2001::/16) on the tunnel interface gif0 fixes it.
The problem is that I'm ultimately planning on having a shell script do all of this on boot, and having the script wait a given number of seconds before deleting and readding the route doesn't seem very elegant, not to mention that I don't really know how much time passes before the default route is changed.

This is what my gif0 and en0 interfaces look like:

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gif0: flags=8051<UP,POINTOPOINT,RUNNING,MULTICAST> mtu 1280
        tunnel inet 192.168.0.6 --> 216.66.80.30
        inet6 fe80::217:f2ff:fed9:eb5e%gif0 prefixlen 64 scopeid 0x2
        inet6 2001:470:1f0b:1393::2 --> 2001:470:1f0a:1393::1 prefixlen 128

This is the default gateway that I manually set (and works):

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Internet6:
Destination                             Gateway                         Flags         Netif Expire
default                                 2001:470:1f0a:1393::1           UGSc   

And this is what it gets reset to (and stops working):

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Internet6:
Destination                             Gateway                         Flags         Netif Expire
default                                 fe80::217:f2ff:fed9:eb5e%en0    UGc   

This happens a short while after starting rtadvd, but I can't find anything in the manual pages that refers to the default route. I have used the very same configuration on FreeBSD (by replacing en0 with the correct interface name) and it worked flawlessly, so I'm not sure what the problem is. I suspect that I should add something to rtadvd.conf, because right now I only have a reference to en0 and that may be why the route is redirected there, but I'm not sure how to do that.

Here is my current rtadvd.conf:

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en0:\
        :addrs#1:addr="2001:470:1f0b:1393::":prefixlen#64:tc=ether:nolladdr:

Any hints will be greatly appreciated.

Thank you :)

[cholzhauer]

i assume that your mac is still listening for ra?  you should be able to tell your mac not to listen for RA and thereby keep its static address (and also the default gateway)

[jollino]

Hello,
unfortunately that's not the problem. net.inet6.ip6.accept_rtadv is set to 0, and the only other variable I change is net.inet6.ip6.forwarding (setting it to 1 to act as a gateway for the rest of my local network.)

[cholzhauer]

Interesting; I've never heard of this before.  Is your iMac configured to advertise RA?

[jollino]

Yes, and after I manually delete the wrong default gateway and set the new one, it works perfectly over the network. I just have no idea why it gets reset to a link-local address after starting rtadvd, nor why it only happens once.
For reference, here are the kernel values about the ipv6 stack:

octavarium:~ jollino$ sysctl -a | grep inet6 | sort
net.inet6.icmp6.errppslimit: 500
net.inet6.icmp6.nd6_debug: 0
net.inet6.icmp6.nd6_delay: 5
net.inet6.icmp6.nd6_maxnudhint: 0
net.inet6.icmp6.nd6_mmaxtries: 3
net.inet6.icmp6.nd6_prune: 1
net.inet6.icmp6.nd6_umaxtries: 3
net.inet6.icmp6.nd6_useloopback: 1
net.inet6.icmp6.nodeinfo: 3
net.inet6.icmp6.rediraccept: 1
net.inet6.icmp6.redirtimeout: 600
net.inet6.ip6.accept_rtadv: 0
net.inet6.ip6.auto_flowlabel: 1
net.inet6.ip6.auto_linklocal: 1
net.inet6.ip6.dad_count: 1
net.inet6.ip6.defmcasthlim: 1
net.inet6.ip6.forwarding: 1
net.inet6.ip6.fw.debug: 0
net.inet6.ip6.fw.enable: 1
net.inet6.ip6.fw.verbose: 0
net.inet6.ip6.fw.verbose_limit: 0
net.inet6.ip6.gifhlim: 0
net.inet6.ip6.hdrnestlimit: 50
net.inet6.ip6.hlim: 64
net.inet6.ip6.kame_version: 20010528/apple-darwin
net.inet6.ip6.keepfaith: 0
net.inet6.ip6.log_interval: 5
net.inet6.ip6.maxdynroutes: 1024
net.inet6.ip6.maxfragpackets: 1024
net.inet6.ip6.maxfrags: 8192
net.inet6.ip6.maxifdefrouters: 16
net.inet6.ip6.maxifprefixes: 16
net.inet6.ip6.neighborgcthresh: 1024
net.inet6.ip6.redirect: 1
net.inet6.ip6.rr_prune: 5
net.inet6.ip6.rtexpire: 3600
net.inet6.ip6.rtmaxcache: 128
net.inet6.ip6.rtminexpire: 10
net.inet6.ip6.temppltime: 86400
net.inet6.ip6.tempvltime: 604800
net.inet6.ip6.use_deprecated: 1
net.inet6.ip6.use_tempaddr: 0
net.inet6.ip6.v6only: 0
net.inet6.ipsec6.ah_net_deflev: 1
net.inet6.ipsec6.ah_trans_deflev: 1
net.inet6.ipsec6.debug: 0
net.inet6.ipsec6.def_policy: 1
net.inet6.ipsec6.ecn: 0
net.inet6.ipsec6.esp_net_deflev: 1
net.inet6.ipsec6.esp_randpad: -1
net.inet6.ipsec6.esp_trans_deflev: 1

[jdh]

I had the exact same problem today, however it seemed to go away once I assigned a proper subnet address manually to my en0 interface, rather than using the default-assigned link-local address.  I also didn't bother configuring anything in rtadvd.conf, since with the proper IPv6 address assigned to en0 it's handing out the correct addresses by default.

[jollino]

Could you please list which commands you use? (Feel free to remove the addresses, of course.)
Thank you very much.

[jdh]

While you could fill it in with ifconfig, it's actually easier just to assign the subnet through the System Preferences by setting your IPv6 configuration to manual and entering it there.

In my case, I allocated a /48 to my HE tunnel and used that to setup the tunnel on GIF0, and then picked an address in my assigned /64 to put on my en0 interface.

So basically, an IP address in my routed /48 gets assigned to gif0 using:

ifconfig gif0 inet6 2001:470:b110::bdc:caff/48 alias

...in addition to the usual commands to setup the tunnel.

I then assigned one of the addresses from my routed /64 to en0 via System Preferences -- select en0, choose "Advanced" and select "Configure IPv6: Manually" and enter the following info:

Router: The Server IPv6 address from your tunnel (same as your default route set by the route command when setting up the gif0 interface)
IPv6 Address: Your /64 prefix and a node on your network (ie, 2001:470:1d:403::1)
Prefix Length: 64

Once that's setup, you should be able to just fire up rtadvd by entering "rtadvd en0" without worrying about the rtadvd.conf file, as the daemon will pick up the network configuration from en0 automatically and advertise addresses within that subnet.  Other machines on your network should autoconfigure with addresses in the 2001:xxxx:xxxx:xxxx::/64 subnet and pick up the default route via your iMac.

Note that you may also need to set net.inet6.ip6.accept_rtadv to 1 on the remote computers for them to pick up the stateless autoconfiguration from your iMac and obtain addresses on the routed /64 network.

In the end, my ifconfig for gif0 and en0 reads as follows:

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gif0: flags=8051<UP,POINTOPOINT,RUNNING,MULTICAST> mtu 1280
       tunnel inet 192.168.101.101 --> 216.66.38.58
       inet6 2001:470:b110::bdc:caff prefixlen 48
       inet6 2001:470:1c:403::2 --> 2001:470:1c:403::1 prefixlen 128
en0: flags=8863<UP,BROADCAST,SMART,RUNNING,SIMPLEX,MULTICAST> mtu 1280
       ether 00:23:df:91:9e:92
       inet6 fe80::223:dfff:fe99:9f93%en0 prefixlen 64 scopeid 0x4
       inet6 2001:470:1d:403::1 prefixlen 64 autoconf
       inet 192.168.101.101 netmask 0xffffff00 broadcast 192.168.101.255
       media: autoselect (1000baseT <full-duplex,flow-control>)
       status: active


[jollino]

I'd rather stay with ifconfig for "portability" on other machines if needs be, but I can't really make it work. I only have a /64 assigned by HE, and I can't pinpoint where the problem is. Here is what I run, including assigning a /64 node to gif0:

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ifconfig gif0 tunnel 192.168.0.6 216.66.80.30
ifconfig gif0 inet6 2001:470:1f0b:1393::1 2001:470:1f0a:1393::1 prefixlen 128
ifconfig gif0 inet6 2001:470:1f0b:1393::aaaa prefixlen 64 alias #what you suggested
ifconfig en0 inet6 2001:470:1f0b:1393::abcd prefixlen 64
route -n add -inet6 default 2001:470:1f0a:1393::1
rtadvd en0

I have cleaned up /etc/rtadvd.conf so everything is commented out. This is what my interfaces look like:

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gif0: flags=8051<UP,POINTOPOINT,RUNNING,MULTICAST> mtu 1280
        tunnel inet 192.168.0.6 --> 216.66.80.30
        inet6 fe80::217:f2ff:fed9:eb5e%gif0 prefixlen 64 scopeid 0x2
        inet6 2001:470:1f0b:1393::1 --> 2001:470:1f0a:1393::1 prefixlen 128
        inet6 2001:470:1f0b:1393::aaaa prefixlen 64
en0: flags=8863<UP,BROADCAST,SMART,RUNNING,SIMPLEX,MULTICAST> mtu 1500
        ether 00:17:f2:d9:eb:5e
        inet6 fe80::217:f2ff:fed9:eb5e%en0 prefixlen 64 scopeid 0x4
        inet 192.168.0.6 netmask 0xffffff00 broadcast 192.168.0.255
        inet6 2001:470:1f0b:1393::abcd prefixlen 64
        media: autoselect (100baseTX <full-duplex,flow-control>)
        status: active


I noticed that your en0 says autoconfig, while mine doesn't. It can't be because of the configuration in System Preferences, as you set it manually.

What route command do you use? I have a feeling that if told it "route via gif0 rather than en0", rtadvd wouldn't try to replace it. However, I've been unable to make it digest the -interface modifier, no matter which syntax I tried. What I have to do to make it start working is deleting the default route and readding it:

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route -n delete -inet6 default
route -n add -inet6 default 2001:470:1f0a:1393::1

and that fixes it on all machines.

I'm sure I'm making very stupid mistake somewhere, but I swear I'm learning in the process. :)

Thank you.

[cholzhauer]

ifconfig gif0 inet6 2001:470:1f0b:1393::1 2001:470:1f0a:1393::1 prefixlen 128
ifconfig gif0 inet6 2001:470:1f0b:1393::aaaa prefixlen 64 alias #what you suggested
ifconfig en0 inet6 2001:470:1f0b:1393::abcd prefixlen 64
route -n add -inet6 default 2001:470:1f0a:1393::1

I think you have your addresses messed up.  Shouldn't this be

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ifconfig gif0 create
ifconfig gif0 inet6 2001:470:1f0b:1393::2 2001:470:1f0a:1393::1 prefixlen 128
ifconfig en0 inet6 2001:470:1f0a:1393::abcd prefixlen 64
route -n add -inet6 default 2001:470:1f0b:1393::1


I'm assuming that 2001:470:1f0b:1393::/64 is your tunnel /64 and  2001:470:1f0a:1393::/64 is your routed /64.  If I'm wrong, you need to change the commands above. 

Only ::1 and ::2 are used out of your tunnel /64; if you need more addresses, you need to go to your routed /64

[jollino]

Okay, I'm getting quite confused (and yes, I feel quite stupid... bear with me, upgrading an OS stack to v6 is easier than upgrading one's brain :D)

According to the tunnel details page, 2001:470:1f0b:1393::/64 is my routed /64 and 2001:470:1f0a:1393::/64 is where the tunnel endpoints are taken from. Specifically, 2001:470:1f0a:1393::1/64 is the server address and 2001:470:1f0a:1393::2/64 is the client address.
First question: why is a whole /64 "wasted" for the two endpoints? And why does the details page use the 2001:470:1f0a:1393::1/64 notation? Shouldn't it be 2001:470:1f0a:1393::1/128 as the tunnel endpoints are effectively one IP each?

So, I suppose that I need to use the tunnel /64 addresses with the gif interface exclusively (on my v6 gateway), and the routed /64 for everything else?

I'm going to make some extra tests, I'll report how it goes.

[cholzhauer]

OK, so the code I wrote should say

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ifconfig gif0 create
ifconfig gif0 inet6 2001:470:1f0a:1393::2 2001:470:1f0a:1393::1 prefixlen 128
route -n add -inet6 default 2001:470:1f0a:1393::1


You'd obviously need to add in the line with the IPv4 addresses, eg "ifconfig gif0 tunnel 1.2.3.4 5.6.7.8"

And why does the details page use the 2001:470:1f0a:1393::1/64 notation? Shouldn't it be 2001:470:1f0a:1393::1/128 as the tunnel endpoints are effectively one IP each?

Because the network actually is a /64   I've seen posts that say you can use the rest of the addresses in that range for your stuff, but you're not able to assign DNS to them, so it's pointless.

So, I suppose that I need to use the tunnel /64 addresses with the gif interface exclusively (on my v6 gateway), and the routed /64 for everything else?

Exactly.  Unless you're going to get a /48, use the routed /64 for everything other than your tunnel addresses

why is a whole /64 "wasted" for the two endpoints?

"Just because."  A /64 is the smallest network that most OS's will accept, so that's what is used.

[jollino]

Thank you for the clarifications.
However, I must be still missing something becuse everything works fine until rtadvd starts. After about 15 seconds, the default gateway goes from 2001:470:1f0a:1393::1 to fe80::217:f2ff:fed9:eb5e%en0 and, of course, everything breaks.
Just to be sure, here is what I do:

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ifconfig gif0 tunnel 192.168.0.6 216.66.80.30
ifconfig gif0 inet6 2001:470:1f0a:1393::2 2001:470:1f0a:1393::1 prefixlen 128
ifconfig gif0 inet6 2001:470:1f0b:1393::ffff prefixlen 128 # as per jdh's advice (node from the routed /64, i suppose /128 is fine)
ifconfig en0 inet6 2001:470:1f0b:1393::abcd prefixlen 64 # as per jdh's advice (on en0, the 'prefixlen 64' should help rtadvd 'get' what it can advertise)
route -n add -inet6 default 2001:470:1f0a:1393::1

The very same thing happens whether or not I manually assign the extra addresses to either interface. It all works great until rtadvd's been running for about 15 seconds.

[cholzhauer]

So the tunnel is working...great.

Every gateway I've seen is an fe80 address.  Really, that should work fine because the router is always on the same network as the clients (at least, that's how it's supposed to be)

I'm not sure why changing from 2001 to fe80 breaks it.  (does this break on the tunnel machine or on other machines on the network?)

Which 2001 address are you using for the gateway?

[jollino]

Well, the tunnel has been working since day one, even with the messed up addresses.

However, I tried using the System Preferences method suggested by jdh and it seems to work... I suppose it has a higher priority than ifconfig when it comes to rtadvd. I just used the two original ifconfig settings for gif0 (tunnel 1.2.3.4 5.6.7.8; inet6 2001::1234 2001:abcd) and rtadvd seems to be going. My iPhone and MacBook Pro also got configured correctly.

As for the gateway, I'm using 2001:470:1f0a:1393::1. The problem with the fe80 address is that rtadvd reset it to the en0 link-local address, not the gif0's. Correct me if I'm wrong, but that would mean that all the ipv6 traffic would be routed to the LAN itself... failing miserably. If it used the gif0's fe80 address it would probably work, but for some reason rtadvd takes the 'en0' parameter to the extreme. Again, for some mysterious reason, giving an address to en0 via System Preferences makes it behave. Why doing so through ifconfig makes it dismiss it is beyond me.

As a side note trivia, all of my traffic from this machine originates from the tunnel IP (2001:470:1f0a:1393::2) rather than the address I manually assigned to the en0 (2001:470:1f0b:1393::1984). Not a big deal, at least that has a reverse DNS entry. :)

Thank you all, for the help and for the explanations!