Friday, August 10, 2018

Ran into this one recently on EL7 (CentOS and friends)

IPv6 duplication address detection leaves link local addresses in dadfailed state after a VM cloning operation.

$ ip -6 addr
1: lo: mtu 65536 state UNKNOWN qlen 1000
    inet6 ::1/128 scope host
       valid_lft forever preferred_lft forever
2: ens160: mtu 1500 state UP qlen 1000
    inet6 fe80::4729:d09e:8f22:56c3/64 scope link tentative dadfailed
       valid_lft forever preferred_lft forever
    inet6 fe80::1435:486f:84ad:93ba/64 scope link tentative dadfailed
       valid_lft forever preferred_lft forever
    inet6 fe80::25b4:c63e:38cb:4bcc/64 scope link tentative dadfailed
       valid_lft forever preferred_lft forever

Which led me to take a look at the interface config file

$ cat /etc/sysconfig/network-scripts/ifcfg-Wired_connection_1 | grep IPv6


The default gen_mode is stable-privacy, which led me to take a look at the RFC for address generation.  In particular, the section on the algorithm.

1. Compute a random (but stable) identifier with the expression:
RID = F(Prefix, Net_Iface, Network_ID, DAD_Counter, secret_key)
A secret key that is not known by the attacker. The secret
key SHOULD be of at least 128 bits. It MUST be initialized to
a pseudo-random number (see [RFC4086] for randomness
requirements for security) when the operating system is
installed or when the IPv6 protocol stack is "bootstrapped"
for the first time. An implementation MAY provide the means
for the system administrator to display and change the secret
The systems in question are using NetworkManager, which led to me to here

$ sudo ls -l /var/lib/NetworkManager/


There can be a lot of cruft (left over state from cloning) in this directory but the secret_key is what we are looking for.

The easy solution and most correct solution is to simply nuke the Ethernet connection in NetworkManager and recreate it.

In this case, the original sysconfig/ifcfg-interface file didn't have a HWADDRESS configured so a new NetworkManager connection wasn't automatically regenerated when a new vNIC showed up after a clone.

And so we have our root cause...

The lesson: Don't remove HWADDRESS from your ifcfg-interface files.

Saturday, December 20, 2014


I took a trip to Vermont recently.  I ate some good food, met some good folks and just generally had a very nice time.

I really wanted to see that part of the country.

Thursday, March 15, 2012


I'm fascinated by the idea of a having a new way to get where I'm going.

It might be a forest trail in an urban park near my house rather than walking the dog on a sidewalk 300 meters and a world away.

Or it might be riding a bike on a trail through my city and seeing an entirely different point of view from that which you get looking out of a car on traveling the streets. Same city, different experience entirely.

Or it even be going out of my way and taking a tourist train from the next city over instead of calling for a ride from the airport :-)

These alternatives are just that - different ways to experience the same places but in a way that feels more connected, more thoughtful and slowed-down.

We humans desire connectedness and in fact we go crazy when we are isolated.

Friday, December 2, 2011

Once in a while

I take a break and let life wash over me . Today is going to be a day for that.

Took the girls to school today. It's amazing how the simplest things can be so enjoyable.

Thursday, August 5, 2010

Google Wave

So sad to see Google throw in the towel on Google Wave.

In retrospect the obvious is pretty clear - the way to get mass wave adoption was to build a really solid bridge between SMTP, IM, and Twitter/ostatus worlds.

Yes, I know people did build those all of those connections and more but the wave team was a fairly small team and they didn't focus on making any of those Google production ready which would have led to people coming to depend on them as a primary inbox type of application.

I still think the concept of a live, read/write, communicating web world is where we are headed.  Wave was definitely ahead of its time.

Sunday, July 4, 2010

Long trip

The trip home was longer than normal. I was able to use public transport the whole way.

On the way home I walked past St. Bernard's church - it was the first day of the combined parish. The bells started ringing and the sky was pure blue on a warm summer day. Perfection!

Tuesday, June 22, 2010

School days

We're meeting with the principal and teacher in a bit...