dhcpcd-discuss

On 28/09/17 09:18, harald.albrecht wrote:
> Graham,
> true, the MSRO is only a side discussion not really relevant to your case, except for the priority field that not only applies to the MSRO but has also been retrofitted to the RA "body" itself.
> While that shouldn't be an issue here, it looks strange that you see a high priority 01 instead of the default medium priority 00. At least that fits in to some extend why your route table entries show two route entries per destination. The thing I don't understand in your router table: why are there the same routes with just +-1 priority step for eth0 and eth1. What link setup do you use?

The high priority setting is there in radvd.conf, with everything set to
"high".  I'll take it out and let you know if it changes anything
substantial.

Oh, you mean eth1 and eth2?  They're plugged into the same network.  So
if I unplug eth2 it still gets the /128 and the routes are like this:

fd70:a6a5:a58b:3:ffff:ffff:ffff:fffe dev eth1  proto kernel  metric 256
expires 17414sec pref medium
fd70:a6a5:a58b:3::/64 dev eth1  metric 203  mtu 1280 pref medium
fe80::/64 dev eth0  proto kernel  metric 256  pref medium
fe80::/64 dev eth1  proto kernel  metric 256  pref medium
fe80::/64 dev eth3  proto kernel  metric 256  pref medium
default via fe80::a00:27ff:fe5d:6607 dev eth1  metric 203  mtu 1280 pref
medium

eth0 has a static IPv4 address and eth3 is set up for dynamic
configuration but not connected to anything.  The default route at the
end is pointing to the router sending the announcements and DHCP
configuration.  I can see where dhcpcd sets that and it all looks correct.

> Did you already check using rdisc6 (router discovery) tool from the optional ndisc6 package what router advertisements get sent when you poke the routers?

I have been using rdisc6 and it gives results like this with different
prefixes according to the current setup:

Soliciting ff02::2 (ff02::2) on eth1...

Hop limit                 :           64 (      0x40)
Stateful address conf.    :          Yes
Stateful other conf.      :           No
Router preference         :         high
Router lifetime           :         1800 (0x00000708) seconds
Reachable time            :  unspecified (0x00000000)
Retransmit time           :  unspecified (0x00000000)
 Prefix                   : fd70:a6a5:a58b:3::/64
  Valid time              :        86400 (0x00015180) seconds
  Pref. time              :        14400 (0x00003840) seconds
 MTU                      :         1280 bytes (valid)
 Source link-layer address: 08:00:27:5D:66:07
 from fe80::a00:27ff:fe5d:6607


Another detail: after about a minute the /128 addresses get deleted:

Sep 28 10:07:58 [5776]: eth1: deleted address
fd70:a6a5:a58b:3:ffff:ffff:ffff:fffe/128

I can see where this happens in the code, but I don't know why.
Although if it's because the prefix is unknown that's fine.  I want to
get the prefix right.


                       Graham


> Best regards,Harald
> 
> -------- Ursprüngliche Nachricht --------Von: Graham Breed <graham.breed@xxxxxxxxxxxxxx> Datum: 28.09.17  09:58  (GMT+01:00) An: "harald.albrecht" <harald.albrecht@xxxxxxx>, dhcpcd-discuss@xxxxxxxxxxxx Betreff: Re: [dhcpcd-discuss] DHCPv6 addresses being assigned with /128
>   prefixes 
> On 27/09/17 20:50, harald.albrecht wrote:
> 
>> Correct, that's RFC 4191. Very useful, for example, when you have subnets that do not only contain hosts but also downstream routers. Unfortunately, some Linux systems have set the maximum MSRO prefix length to 0 which disables learning of these routes. It can be reenabled via sysctl, but it's unfortunate that this is even necessary.
> 
> Yes, looks useful, but I'm not advertising downstream routers so it
> shouldn't be required.  According to Wireshark, I have a "Prf High (1)"
> field in the Router Advertisement header.  Then I have a Prefix
> Information field but no Router Information.
> 
> 
>                       Graham
> 

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