[Xen-users] Re: dhcp service in Dom0 not working properly

["Alejandro Martini" <alejandro.martini@xxxxxxxxx>]

I forgot to mention one more thing that might help to debug the issue or isolate the problem.

tshark shows that eth0 can actually see DHCPINFORM packets broadcasted on the LAN, but it does not see DHCPDISCOVERs nor DHCPREQUESTs. 

The only obvious difference that i can see between DHCPINFORM packets and the other ones, is that the first ones come from specific addresses (client machines that already have their ip addresses set). The other dhcp packet types (seen by peth0 but not by eth0) have 
0.0.0.0 as their source address. 


Alex

2007/8/27, Alejandro Martini <alejandro.martini@xxxxxxxxx >:

Following Tibor's advice, i disabled tx checksums for the eth0 interface, and then run some more tests. Here's what i've found by running two instances of tcpdump simultaneously (one listening on eth0, and the other listening on peth0):

Dump 1 (listening on peth0):

tcpdump -vv -i peth0 'dst port 67 or src port 68'
tcpdump: WARNING: peth0: no IPv4 address assigned
tcpdump: listening on peth0, link-type EN10MB (Ethernet), capture size 96 bytes
18:46:42.413530 IP (tos 0x0, ttl 128, id 6463, offset 0, flags [none], proto: UDP (17), length: 328) 0.0.0.0.bootpc > 255.255.255.255.bootps: BOOTP/DHCP, Request from 00:16:17:3b:5e:33 (oui Unknown), length 300, xid 0x9f266e11, secs 7168, Flags [ Broadcast ] (0x8000)

Dump 2 (listening on eth0, nothing happens):

tcpdump -vv -i eth0 'dst port 67 or src port 68'
tcpdump: listening on eth0, link-type EN10MB (Ethernet), capture size 96 bytes

One can conclude that DHCPDISCOVER packets are reaching the server (as peth0 sees them perfectly). However, those same packets don't get to eth0. I repeated the test with tshark, leaving it running for a couple of hours, and while peth0 saw every dhcp broadcast on the network, eth0 didn't see a single one.

Is this an expected Xen behaviour? Is there a solution or workaround to circumvent this problem?


Thanks again,
Alex

2007/8/26, Alejandro Martini < alejandro.martini@xxxxxxxxx>:

I have the following problem. I've set up a dhcp server at Dom0 level, in order to provide ip addresses for the computers on my LAN. However, the dhcp daemon is not answering queries, nor giving addresses.

Dom0 has just one ethernet adapter configured (the physical machine has only one ethernet card, which is connected to the LAN switch).

The dhcp daemon is running and listening (that's at least what netstat shows), with no errors reported to the system logs. I don't think it can be an iptables issue, since it seems that dhcp packets don't pass through the iptables chains (anyways, i also tried allowing all traffic -setting default INPUT policy == ACCEPT-, but that didn't help).

If i try a tcpdump -i eth0 'dst port 67', i can't even see DHCPREQUEST packets reaching the server (client machines, based on W2K, keep retrying until they give up, wihtout getting a valid address). I must note that connectivity on Dom0 works ok, with several services working as expected (dns, http, squid, etc.)

The server is running Debian Etch (the dhcp service configuration was copied from a physical server, in which it was working fine).

Has anyone experienced similar problems? Any ideas on how this can be fixed?


Thanks in advance,
Alex

====================================================

ii  xen-hypervisor-3.0.3-1-i386-pae   3.0.3-0-2                       The Xen Hypervisor on i386 with pae
ii  dhcp3-server                      3.0.4-13                        DHCP server for automatic IP address assignm

Linux version 2.6.18-4-xen-686 (Debian 2.6.18.dfsg.1-12etch2) ( dannf@xxxxxxxxxx) (gcc version 4.1.2 20061115 (prerelease) (Debian 4.1.1-21))

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