Re: [Xen-users] Basic Network Bridge

[Alexandre Kouznetsov <alk@xxxxxxxxxx>]

El 22/06/12 14:54, Eric Lindsey escribió:
> This from dom0 (www):
> 15:39:30.506858 IP 0.0.0.0.68>  255.255.255.255.67: BOOTP/DHCP,
> Request from 00:16:3e:5a:65:3c, length 300
> 15:39:30.506993 IP 10.1.20.1.67>  10.1.20.110.68: BOOTP/DHCP, Reply, length 305
Your exchange is abnormal. Take a look on this good one:

15:46:25.031591 IP 0.0.0.0.68 > 255.255.255.255.67: BOOTP/DHCP, Request 
from 00:26:6c:10:5a:4d, length 300
15:46:26.002892 IP 10.13.36.253.67 > 255.255.255.255.68: BOOTP/DHCP, 
Reply, length 300
15:46:26.004265 IP 0.0.0.0.68 > 255.255.255.255.67: BOOTP/DHCP, Request 
from 00:26:6c:10:5a:4d, length 316
15:46:26.033630 IP 10.13.36.253.67 > 255.255.255.255.68: BOOTP/DHCP, 
Reply, length 305
There are four messages involved:
Client: I need IP! (DHCPDISCOVER)
Server: have X available for you (DHCPOFFER)
Client: I request X! (DHCPREQUEST)
Server: your use of X is acknowledged (DHCPACK)

After that, the client only renews the lease, so the server is aware of 
this lease steel being needed. They only exchange DHCPREQUEST and 
DHCPREQUEST, unless a DHCPREQUEST is denied for some reason.
So, in your case, there are two details:
1. Only two messages are visible, not four.
2. DHCP server sends replay to 10.1.20.110.68, not 255.255.255.255.68

I think your dnsmasq is treating your client as if it had a valid 
leases, while your client feels completly new. Probably, cleaning the 
leases cache would solve the issue (/var/lib/misc/dnsmasq.leases).
Check your Dnsmasq configuration to make sure this does not happen again.


> Haha I can't install tcpdump on domU because it has no Internet access.
> Assigned static information on domU in /etc/network/interfaces, and
> everything is golden.  DNS works, Internet works, network works!
That isolates the issue to DHCP service, converting this thread in a 
offtopic (:
> Is my dom0 trying to send the DHCPOFFER directly to a specific IP
> address (10.1.20.110 from the look of things) when the eth0 interface
> on domU doesn't have an address yet (hence the DHCP request)?
That's the point.

--
Alexandre Kouznetsov

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