It would be useful to get full packet dumps rather than just tcpdump
output.

It would also be useful to run dnsmasq under strace and see what
syscalls it's making: that would tell use where the reply might be going.


Cheers,

Simon.




On 03/01/2019 07:41, Sandeep K M wrote:
> Hi All,
> 
>  
> 
> I have a simple setup with a relay agent as shown below:
> 
> 
> +----------+-------------+
> |    dnsmasq server |
> 
> |         (ubuntu)         |
> 
> +-------------------------+
>                 | m1s1p7 (1040::2/120)
>                 | (IP route : 2020::/120 via 1040::1 dev m1s1p7  proto
> static  metric 512  pref medium)
>                 |
>                 |
>                 | 1/1/2 (1040::1/120)
> +----------+------------+
> |        Switch            |
> |     (Relay Agent )  |
> +-----------------------+
>                 | 1/1/1 (2020::1/120) 
>                 |
>                 |     
>                 | eth1     
> +----------+--------------+
> |     Client (Ubuntu)  |
> +--------------------------+
> 
> 
> It is exactly the same as explained in the video :
> https://www.youtube.com/watch?v=2Lt1aXpCzvQ
> 
> 
> Whenever the client is requesting an IPv6 address dnsmasq is failing to
> respond with “DHCPADVERTISE” message. The “DHCPADVERTISE” has not been
> sent via the interface. The tcpdump clearly shows that “DHCPADVERTISE”
> message has not gone through the interface (m1s1p7), its only showing
> the “DHCPSOLICIT” message which has been received:
> 
>  
> 
> /root@8320:~# tcpdump -i *m1s1p7* udp port 547 or 546 -vvv -n/
> 
> //
> 
> /tcpdump: listening on m1s1p7, link-type EN10MB (Ethernet), capture size
> 262144 bytes/
> 
> //
> 
> / /
> 
> //
> 
> /06:32:37.214798 IP6 (hlim 64, next-header UDP (17) payload length: 110)
> 2020::1.547 > 1040::2.547: [udp sum ok] dhcp6 relay-fwd
> (linkaddr=2020::1 peeraddr=fe80::250:56ff:febd:7c93 (relay-message
> (*dhcp6 solicit* (xid=1894f2 (client-ID hwaddr/time type 1 time
> 599811159 005056bd7c93) (option-request DNS-server DNS-search-list
> Client-FQDN SNTP-servers) (elapsed-time 0) (IA_NA IAID:1455258771
> T1:3600 T2:5400))) (interface-ID 00000024...))/
> 
>  
> 
> But the dnsmasq logs shows that it is trying to send the “DHCPADVERTISE”
> message but for some reason it’s not been sent via the interface *m1s1p7. *
> 
> * *
> 
> **
> 
> /root@8320:~# tail -f /var/log/dnsmasq_swns/dnsmasq6.log/
> 
> //
> 
> /Jan  3 06:11:20 dnsmasq[4151]: started, version 2.78 DNS disabled/
> 
> //
> 
> /Jan  3 06:11:20 dnsmasq[4151]: compile time options: IPv6 GNU-getopt
> no-DBus no-i18n no-IDN DHCP DHCPv6 no-Lua TFTP no-conntrack ipset auth
> no-DNSSEC loop-detect inotify/
> 
> /Jan  3 06:11:20 dnsmasq-dhcp[4151]: DHCPv6, IP range 2020::10 --
> 2020::20, lease time 1h/
> 
> /Jan  3 06:12:38 dnsmasq-dhcp[4151]: DHCPSOLICIT(m1s1p7)
> 00:01:00:01:23:c0:64:57:00:50:56:bd:7c:93/
> 
> //
> 
> /Jan  3 06:12:38 dnsmasq-dhcp[4151]: DHCPADVERTISE(m1s1p7) 2020::12
> 00:01:00:01:23:c0:64:57:00:50:56:bd:7c:93/
> 
>  
> 
> *Does anyone has any clue on what is going on here ? Am I missing
> something ? Here is my dnsmasq config file contents:*
> 
>  
> 
> /root@8320:~# cat /var/run/dnsmasq_swns/dnsmasq6.conf/
> 
> //
> 
> /enable-ra/
> 
> //
> 
> /log-dhcp/
> 
> //
> 
> /log-queries/
> 
> //
> 
> /log-facility=/var/log/dnsmasq_swns/dnsmasq6.log/
> 
> //
> 
> /port=0/
> 
> //
> 
> /dhcp-script=/usr/bin/dhcp_server_leases/
> 
> //
> 
> /leasefile-ro/
> 
> //
> 
> /dhcp-lease-max=64000/
> 
> //
> 
> /dhcp-range=set:default+test,2020::10,2020::20,120/
> 
>  
> 
> Thanks
> 
> -Sandeep
> 
> 
> 
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