Can't get DHCP IP, may be avahi related

[Terence Simpson]

J. Pablo Fernández wrote:
> Hello Kubuntuers,
> I am experiencing strange problems. I have two notebooks running Kubuntu which 
> have problems getting an IP by DHCP. I've experienced the same issues in 
> three different networks, two wlans and one corporate lan with hundreds of 
> other computers just working (some Windows, some Mac OS X and some Linux).
> Basically the sympthon is that I don't get any IP address. eth0 has no IP(v4) 
> address and there's an eth0:avahi (virtual?) device with a private IP. Now, 
> with enoughs restarts and ifdown ifups I get an IP. I can be 100% sure but it 
> seems that whenever I get an IP the eth0:avahi interfare is not present... I 
> am starting to be suspicious of this avahi thing.
> At the corporate network, when I finally get an IP address, it still doesn't 
> work. Now the sympthon is that I can ping the nameservers but they don't 
> reply to any DNS query. Fair enough, let's see what's going on... a tcpdump 
> doesn't show anything... and I am not talking about DNS, not even the pings 
> are shown, and when I cancel it (^C) I get this:
> $ tcpdump
> tcpdump: verbose output suppressed, use -v or -vv for full protocol decode
> listening on eth0, link-type EN10MB (Ethernet), capture size 96 bytes
> 18:29:54.910460 arp who-has 172.26.128.68 tell 169.254.9.96
>
> 1 packets captured
> 495 packets received by filter
> 148 packets dropped by kernel
>
> Why are there packets dropped? I don't have any firewall in place, my iptables 
> are empty.
> If I keep ifdowning/ifuping, eventually it works, but it takes a lot of tries.
>
> Furthermore, my routing table seems to have some remains of this avahi thing:
> $ route -n
> Kernel IP routing table
> Destination     Gateway         Genmask         Flags Metric Ref    Use Iface
> 172.28.3.0      0.0.0.0         255.255.255.0   U     0      0        0 eth0
> 169.254.0.0     0.0.0.0         255.255.0.0     U     1000   0        0 eth0
> 0.0.0.0         172.28.3.254    0.0.0.0         UG    0      0        0 eth0
>
> but I don't have the avahi thing anymore so I don't have any IPs in the 169... 
> network:
>
> 1: lo: <LOOPBACK,UP,10000> mtu 16436 qdisc noqueue
>     inet 127.0.0.1/8 scope host lo
> 2: eth0: <BROADCAST,MULTICAST,UP,10000> mtu 1500 qdisc pfifo_fast qlen 1000
>     inet 172.28.3.205/24 brd 172.28.3.255 scope global eth0
>
> Isn't it invalid to have such a route? I've tried deleting it, maybe I've got 
> the syntax wrong, but I couldn't do it:
>   
No, that's the avahi route.
> pupeno at silver:~$ sudo route del 169.254.0.0
> SIOCDELRT: No such process
>
> Any ideas what's going on and/or how to fix it? Anyone experiencing something 
> similar?
>
> Thank you
>   

It's unlikely that avahi would stop you getting an IP address, you only 
get an avahi address when you don't get a DHCP/static IP address. Avahi 
won't do anything if you can get a normal IP address.

Terence