[Users] Running DHCP on VPS, ( on a router.. )

[Kirill Korotaev]

Dariush,

BTW, I forgot to ask yo to grab tcpdump output from veth107.0 in HN.
Now from your tcpdumps we see that DHCP request is visible in eth0.107,
bridge br107 interfaces, but we don't know whether bridge has broadcasted
the request to veth107.0

Kirill

Kirill Korotaev wrote:
> Dariush Pietrzak wrote:
> 
>>>>HN: tcpdump -n -i eth0.107
>>>
>>>is it veth pair interface, right? ok...
>>
>> I might not exactly follow the term 'veth pair interface', but eth0.107
>>and veth are joined together by a bridge:
> 
> 
> by pair I mean that veth interface has 2 ends: one inside VE and another one in HN.
> then what is eth0.107? vlan?
> 
> 
>>br107           8000.0018511cf71d       no              eth0.107
>>                                                        veth107.0
>>
>>
>>
>>>and is 192.168.8.254 assigned to veth inside VE?
>>
>> 192.168.8.251 is assigned to veth, .254 is a ucarp-managed IP and it's
>>assigned to br107. 
> 
> 
> so, this means that your host system replies to DHCP request below.
> cause this IP belongs to HN.
> are you running DHCP server in HN as well?
> 
> 
>>>>08:16:19.401880 00:1b:d4:7e:76:2a > 01:00:0c:cc:cc:cd SNAP Unnumbered, ui, Flags [Command], length 50
>>>>08:16:21.154240 IP 0.0.0.0.68 > 255.255.255.255.67: BOOTP/DHCP, Request from 00:1b:d5:2c:bf:38, length 308
>>>>08:16:21.185096 IP 192.168.8.254.67 > 255.255.255.255.68: BOOTP/DHCP, Reply, length 300
>>>>08:16:21.187344 arp who-has 192.168.9.254 tell 192.168.9.97
>>>>
>>>>
>>>>HN: tcpdump -n -i br107
>>>>08:16:19.401880 00:1b:d4:7e:76:2a > 01:00:0c:cc:cc:cd SNAP Unnumbered, ui, Flags [Command], length 50
>>>>08:16:21.154240 IP 0.0.0.0.68 > 255.255.255.255.67: BOOTP/DHCP, Request from 00:1b:d5:2c:bf:38, length 308
>>>>08:16:21.185096 IP 192.168.8.254.67 > 255.255.255.255.68: BOOTP/DHCP, Reply, length 300
>>>>08:16:21.187344 arp who-has 192.168.9.254 tell 192.168.9.97
>>>>
>>>>and finally, from inside the vps:
>>>>VPS: tcpdump -n -i eth0
>>>>08:16:19.401886 00:1b:d4:7e:76:2a > 01:00:0c:cc:cc:cd SNAP Unnumbered, ui, Flags [Command], length 50
>>>>08:16:21.185110 IP 192.168.8.254.67 > 255.255.255.255.68: BOOTP/DHCP, Reply, length 300
>>>>08:16:21.187356 arp who-has 192.168.9.254 tell 192.168.9.97
>>>>08:16:21.188600 arp who-has 192.168.8.1 tell 192.168.9.97
>>>
>>>I wonder why timestamp of Reply here is greater then timestamp in HN...
>>
>> yes, it looks strange, especially since the next packet - arp req, has
>>similarly delayed timestamp, like something in veth delayed packets after
>>dhcp req/reply sequence.
>> This delay is visible here: .401880 on bridge and eth0.107, but .401886
>>from veth. But this .000006 grows to .000014 and then shrinks to .000012 
>>after missing the packet.
> 
> 
> if my logic above about DHCP server in HN is correct, then no wonder... :)
> 
> 
>>>to DHCP requests and you see the reply only. Can you please check (if it is true - shutting down
>>>dhcp server inside VE won't affect tcpdump output)?
>>
>> This is true, but why do some packets visible on bridge and physical
>>interface disappear on veth? When I disable the other dhcp server there is
>>no reply at all. dhcpd doesn't see the packet.
> 
> 
> I guess this can be due to veth filtering which I removed by the patch I send you.
> This filtering drops the packets which should not be seen by VE.
> If the patch helps - I'm right.
> 
> 
>>>>as you can see, broadcast request from dhcp client is missing, but strangely enough, the reply
>>>>is clearly visible.
>>>
>>>Or it works, but only tcpdump is missing the packet?
>>
>> That would be possible, but still puzzling, and that wouldn't explaing why
>>both tcpdump and dhcpd are missing the packet. 
>> Besides, this machine is very lightly loaded at the moment, and the
>>traffic at hand is also abysmally small, not to mention that this happens quite regularly, almost 
>>all dhcp requests get lost and never arrive to my dhcpd. 
> 
> 
> 
> Thanks,
> Kirill
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