Forum - rtadvd and IPv6 routing on OpenBSD 4.2 :: SixXS

rtadvd and IPv6 routing on OpenBSD 4.2

Shadow Hawkins on Thursday, 03 April 2008 18:53:00

Perhaps I'm missing something in my config but my Vista clients are getting my router's link local address for a default gateway. Should I be using DHCPv6 instead? Also, is DHCP so far the only way to advertise a IPv6 nameserver? I've read that rtadvd may provide this in the future but I'm not seeing any config examples that suggest it's possible. Here's my router: $ cat /etc/rtadvd.conf fxp0:\ :addr="2001:4978:15f::":prefixlen#48:tc=ether: $ ifconfig fxp0 fxp0: flags=8843<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST> mtu 1500 lladdr 00:03:47:0a:a7:61 media: Ethernet autoselect (100baseTX full-duplex) status: active inet 192.168.1.2 netmask 0xffffff00 broadcast 192.168.1.255 inet6 fe80::203:47ff:fe0a:a761%fxp0 prefixlen 64 scopeid 0x1 inet6 2001:4978:15f::1 prefixlen 48 and client: Description . . . . . . . . . . . : Broadcom NetXtreme Gigabit Ethernet Physical Address. . . . . . . . . : 00-0D-56-DD-C3-4C DHCP Enabled. . . . . . . . . . . : Yes Autoconfiguration Enabled . . . . : Yes Link-local IPv6 Address . . . . . : fe80::c184:dc27:dd06:674d%9(Preferred) IPv4 Address. . . . . . . . . . . : 192.168.1.33(Preferred) Subnet Mask . . . . . . . . . . . : 255.255.255.0 Lease Obtained. . . . . . . . . . : Thursday, April 03, 2008 9:38:31 AM Lease Expires . . . . . . . . . . : Wednesday, April 09, 2008 9:38:35 AM Default Gateway . . . . . . . . . : fe80::203:47ff:fe0a:a761%9 0.0.0.0 192.168.1.1 DHCP Server . . . . . . . . . . . : 192.168.1.3 DNS Servers . . . . . . . . . . . : 192.168.1.3 NetBIOS over Tcpip. . . . . . . . : Enabled thanks, Gary

rtadvd and IPv6 routing on OpenBSD 4.2

Shadow Hawkins on Thursday, 03 April 2008 19:12:01

Perhaps I'm missing something in my config but my Vista clients are getting my router's link local address for a default gateway.

Which is perfectly fine. It works. That is how others have it too. David

rtadvd and IPv6 routing on OpenBSD 4.2

Shadow Hawkins on Thursday, 03 April 2008 19:13:08

As for DNS, see the second half of this forum thread : https://noc.sixxs.net/forum/?msg=general-695535

rtadvd and IPv6 routing on OpenBSD 4.2

Shadow Hawkins on Thursday, 03 April 2008 20:02:24

It works if I statically set my router's internal IP as my gateway -- but not for stateless config. The default route on my client ends up being router's link local address. Is that supposed to work? Because it's not. I guess I'll be compiling ISC's latest build of DHCP on my router since the Win2k8 scope I've set up is being ignored as well. -Gary

rtadvd and IPv6 routing on OpenBSD 4.2

Shadow Hawkins on Thursday, 03 April 2008 21:23:13

Please forgive my ignorance on this topic. Do I need to do something like this? http://mucc.mahidol.ac.th/~ccvvs/isatap.html#router-config

rtadvd and IPv6 routing on OpenBSD 4.2

Shadow Hawkins on Friday, 04 April 2008 08:52:32

Did you read this : https://noc.sixxs.net/faq/connectivity/?faq=usingsubnet ?

rtadvd and IPv6 routing on OpenBSD 4.2

Jeroen Massar SixXS Staff

on Thursday, 03 April 2008 23:35:55

$ cat /etc/rtadvd.conf

fxp0:\

:addr="2001:4978:15f::":prefixlen#48:tc=ether:

[..]

inet6 2001:4978:15f::1 prefixlen 48

That should be a 64 there, not 48. Links are /64's, sites are /48s. I guess it is time for a dedicated FAQ about this explaining the differences. And one can also use RA to advertise a nameserver, but not every rtadvd/client combo supports this. Then again dhcpv6 is not default either, thus one need to install some software anyway.

rtadvd and IPv6 routing on OpenBSD 4.2

Shadow Hawkins on Friday, 04 April 2008 18:11:10

Thanks, that did the trick! Does anyone know if the KAME stack supports name server announcement? I can get a manual address now but still need to supply the nameserver address. DHCP 4.1.0a1 doesn't seem to be doing its job. Perhaps this is another area that's confusing -- can you use RA in conjunction with DHCPv6 or should you choose one or the other? much thanks, Gary

rtadvd and IPv6 routing on OpenBSD 4.2

Jeroen Massar SixXS Staff

on Friday, 04 April 2008 19:42:56

Well, this is the reason why there are fat books about IPv6 ;) But the trick is simple (sort of), from radvd.conf manual page on a Debian box and likely available elsewhere and in the given RFC's:

AdvManagedFlag on|off When set, hosts use the administered (stateful) protocol for address autoconfiguration in addition to any addresses autoconfigured using stateless address autoconfiguration. The use of this flag is described in RFC 2462.

In other words, when you are going to do DCHPv6, you run a Router ADVertisement Daemon, which then, because clients receive RA's tell the client "if you want more configuration, then ask DHCP". (DHCP is afaik the only stateless protocol which fits that bill). DHCP is in this case used for "addresses", RA is only used to explain that to the client. There also is:

AdvOtherConfigFlag on|off When set, hosts use the administered (stateful) protocol for autoconfiguration of other (non-address) information. The use of this flag is described in RFC 2462.

Which effectively means "configure your address using RA, but configure your nameservers/timeservers/etc using DHCP. So, yes, you can run both at the same time and most likely you will. Unless you avoid DHCP altogether. Mostly you will have IPv4 + IPv6 in a network, thus use DHCPv4 to configure IPv4 and provide nameservers, while using RA for configuring IPv6 addresses.

rtadvd and IPv6 routing on OpenBSD 4.2

Shadow Hawkins on Friday, 04 April 2008 23:59:14

A dual stack config is working ok for me now. Thanks for everyone's feedback. It looks I'll have to experiment with the raflags in my config to see if it'll force my clients to talk to DHCPv6. Ideally, I'd like to be able to switch seamlessly between dual stack and v6 native. -Gary

rtadvd and IPv6 routing on OpenBSD 4.2

Jeroen Massar SixXS Staff

on Saturday, 05 April 2008 00:04:26

Why would you want to drop IPv4? You would miss most of the Internet if you did that.

rtadvd and IPv6 routing on OpenBSD 4.2

Shadow Hawkins on Saturday, 05 April 2008 00:35:54

Just for testing purposes. Ironically, the fora here are not reachable with IPv4 turned off. I got it working after found a useful flag setting (raflags#64) here: http://www.kame.net/newsletter/20030411. Now in dual mode and v6 only I have an IPv6 address for my primary name server. On to other OS clients now. I've read that OS X Leopard requires a bit of kludging but I'll probaby try a Linux or BSD client first. I can't remember where I read of a way to compile your own DHCPv6 client but it might have been in here somewhere: http://www.civil-tongue.net/6and4 -Gary

rtadvd and IPv6 routing on OpenBSD 4.2

Shadow Hawkins on Sunday, 06 April 2008 20:16:16

This Cisco paper on <a href="http://www.cisco.com/en/US/prod/collateral/iosswrel/ps6537/ps6554/ps6600/ps6641/aag_C45-456070_v2.pdf">DHCPv6</a> has a good explanation of how it works with RA. So when I'm setting my RA flags in the rtadvd.conf, do I want to put in the decimal equivalent of x80 plus x40 (C0 or, 128+64=192), raflags#192? -Gary

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