Kai Schaetzl wrote:
>
> I'm trying to get DHCP working with DomU clients. I don't want to use
> libvirtd. There's a dhcpd on the machine and it works fine for all clients
> in the network, but not for DomUs. If I set a static IP on the DomU all
> networking for them is fine, so there's no general networking problem.
>
> I use the xen 3.2 packages for CentOS on CentOS 5.1.
>
> There was a public IP address on eth0 and a private IP address on eth0:0.
> I changed that around after I discovered with tcpdump that dhcpd was
> replying on eth0 like publicip.bootps -> privateip.bootpc. This isn't a
> problem for all other packets, but apparently for DHCP.
>
> Bridging is setup with the standard Xen 3.2 network-bridge script by xend
> like this:
>
> bridge name bridge id STP enabled interfaces
> eth0 8000.000c6e101f84 no vif3.0
> vif2.0
> vif1.0
> peth0
>
> Once I had the private IP address on eth0 and not on the alias anymore
> DHCP started working on DomUs. However, I had to discover it worked only
> for this first bootup and not later on. The DomU starts up, gets an IP
> assigned and is happy. However, when it comes to renew the lease it hits
> the same problem as before. There's first DHCPREQUEST, no answer, then
> DHCPDISCOVER, no answer, it eventually falls back to pinging the gateway
> (which works) and then stops. Eventually it drops it's own IP.
> Sometimes it starts working after a reboot of the host, sometimes not.
> Actually, there's not "no answer", it's just that the reply doesn't make
> it to the DomU. tcpdump shows the reply on peth0, but not on eth0. Here's
> an example from peth0:
>
> 15:59:41.964744 IP (tos 0x10, ttl 16, id 0, offset 0, flags [none],
> proto: UDP (17), length: 328) 0.0.0.0.bootpc >
> 255.255.255.255.bootps:
> BOOTP/DHCP, Request from 00:16:3e:43:17:01 (oui Unknown),
> length: 300,
> xid:0x4e682b4f, secs:50, flags: [none] (0x0000)
> Client Ethernet Address: 00:16:3e:43:17:01 (oui Unknown)
> [|bootp]
> 15:59:41.965540 IP (tos 0x10, ttl 16, id 0, offset 0, flags [none],
> proto: UDP (17), length: 328) mambo.bolera.lan.bootps >
> 192.168.1.149.bootpc: BOOTP/DHCP, Reply, length: 300, xid:0x4e682b4f,
> secs:50, flags: [none] (0x0000)
> Your IP: 192.168.1.149
> Client Ethernet Address: 00:16:3e:43:17:01 (oui Unknown)
> [|bootp]
>
> eth0 sees only the first packet. So, there is something necessary to make
> the DHCP packet travel from peth0 to eth0. I tried several routing and ip
> tables commands, nothing helps.
>
> What is necessary to make DHCP in DomUs work?
Gee, Kai, you've had the worse problems with your Xen setup.
What happens if you disable the eth0:0 alias temporarily?
-Ross
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