Discussion:
Ubuntu Isc-Dhcp 4.2.4 and disable IPv6 !
CpServiceSPb .
2016-03-16 22:05:32 UTC
Permalink
I have isc-dhcp-server installed at ubuntu 14.04 x64.
Its version is 4.2.4

I have fully disabled IPv6 at OS.
Also I have "-4" option for dhcp server startup.

But there is one IPv6 listened address by netstat -anupt.
Port is dyynamic.


What is this dynamically defined port intended for ?

And how is to fully disable IPv6 listening ?
Nicolas C.
2016-03-17 12:39:55 UTC
Permalink
Post by CpServiceSPb .
I have isc-dhcp-server installed at ubuntu 14.04 x64.
Its version is 4.2.4
I have fully disabled IPv6 at OS.
Also I have "-4" option for dhcp server startup.
But there is one IPv6 listened address by netstat -anupt.
Port is dyynamic.
What is this dynamically defined port intended for ?
And how is to fully disable IPv6 listening ?
Hello,

What makes you think that this is caused by the DHCP server? Can you
give us the output of your "netstat" command? Is the dhcpd service
listening to an IPv6 address? Maybe a "ps -ef | grep dhcpd" will give us
a hint.

Try disabling IPv6 by adding "ipv6.disable=1" on the
GRUB_CMDLINE_LINUX_DEFAULT variable in the /etc/default/grub file, then
run "update-grub" and reboot. But there's little chance that the DHCP
server has anything to do with your problem because it is not dual-stack
: it can operate only for one protocol at the time (DHCPv4 *or* DHCPv6).

Have a nice day,
CpServiceSPb .
2016-03-17 14:38:53 UTC
Permalink
Hi.
Output of netstat command made me think.
Let' s look:

tcp 0 0 127.0.0.1:5038 0.0.0.0:*
LISTEN 27158/asterisk
tcp 0 0 0.0.0.0:80 0.0.0.0:*
LISTEN 911/apache2
tcp 0 0 10.10.0.254:82 0.0.0.0:*
LISTEN 911/apache2
tcp 0 0 127.0.0.1:82 0.0.0.0:*
LISTEN 911/apache2
tcp 0 0 10.10.0.254:53 0.0.0.0:*
LISTEN 2167/named
tcp 0 0 127.0.0.1:53 0.0.0.0:*
LISTEN 2167/named
tcp 0 0 10.10.0.254:5432 0.0.0.0:*
LISTEN 1635/postgres
tcp 0 0 127.0.0.1:5432 0.0.0.0:*
LISTEN 1635/postgres
tcp 0 0 127.0.0.1:953 0.0.0.0:*
LISTEN 2167/named
tcp 0 0 127.0.0.1:5432 127.0.0.1:59125
ESTABLISHED 27198/postgres: ast
tcp 0 0 127.0.0.1:59125 127.0.0.1:5432
ESTABLISHED 27158/asterisk
udp 0 0 0.0.0.0:5060 0.0.0.0:*
27158/asterisk
udp 0 0 127.0.0.1:41958 127.0.0.1:41958
ESTABLISHED 1635/postgres
*udp 0 0 0.0.0.0:40895 <http://0.0.0.0:40895>
0.0.0.0:* 12116/dhcpd*
udp 0 0 10.10.0.254:53 0.0.0.0:*
2167/named
udp 0 0 127.0.0.1:53 0.0.0.0:*
2167/named
*udp 0 0 0.0.0.0:67 <http://0.0.0.0:67>
0.0.0.0:* 12116/dhcpd*
udp 125440 0 0.0.0.0:68 0.0.0.0:*
10681/charon
udp 0 0 10.10.0.254:123 0.0.0.0:*
1290/ntpd
udp 0 0 127.0.0.1:123 0.0.0.0:*
1290/ntpd

*udp6 0 0 :::39873
:::* 12116/dhcpd*


I will try to change grubconf.
But I turned off IPv6 completely by sysctl.d.

With wishes of many good things.
Post by Nicolas C.
Post by CpServiceSPb .
I have isc-dhcp-server installed at ubuntu 14.04 x64.
Its version is 4.2.4
I have fully disabled IPv6 at OS.
Also I have "-4" option for dhcp server startup.
But there is one IPv6 listened address by netstat -anupt.
Port is dyynamic.
What is this dynamically defined port intended for ?
And how is to fully disable IPv6 listening ?
Hello,
What makes you think that this is caused by the DHCP server? Can you give
us the output of your "netstat" command? Is the dhcpd service listening to
an IPv6 address? Maybe a "ps -ef | grep dhcpd" will give us a hint.
Try disabling IPv6 by adding "ipv6.disable=1" on the
GRUB_CMDLINE_LINUX_DEFAULT variable in the /etc/default/grub file, then run
"update-grub" and reboot. But there's little chance that the DHCP server
has anything to do with your problem because it is not dual-stack : it can
operate only for one protocol at the time (DHCPv4 *or* DHCPv6).
Have a nice day,
Nicolas C.
2016-03-17 15:25:10 UTC
Permalink
[...]
*udp6 0 0 :::39873 :::* 12116/dhcpd
According to this bug report, it's caused by the nsupdate capability of
dhcpd :

https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=712503

It probably means that even though dhcpd is running in DHCPv4 mode, it
will perform DDNS (dynamic updates of DNS zones) with nsupdate either on
IPv4 or IPv6 protocol. So this is why you see dhcpd listening in IPv6.

My personal opinion is that's not really a bug : if the DHCP server has
an IPv6 connectivity with the DNS server, why not use IPv6 regardless of
the type of addresses that are being updated ?

Regards,

Nicolas
CpServiceSPb .
2016-03-17 15:35:59 UTC
Permalink
Hi again.
Adding of GRUB_CMDLINE_LINUX_DEFAULT="ipv6.disable=1"
to /etc/default/grub allowed to avoid listening of ipv6 port by dhcpd.

Thanks.

With wishes of many good things.
Post by CpServiceSPb .
Hi.
Output of netstat command made me think.
tcp 0 0 127.0.0.1:5038 0.0.0.0:*
LISTEN 27158/asterisk
tcp 0 0 0.0.0.0:80 0.0.0.0:*
LISTEN 911/apache2
tcp 0 0 10.10.0.254:82 0.0.0.0:*
LISTEN 911/apache2
tcp 0 0 127.0.0.1:82 0.0.0.0:*
LISTEN 911/apache2
tcp 0 0 10.10.0.254:53 0.0.0.0:*
LISTEN 2167/named
tcp 0 0 127.0.0.1:53 0.0.0.0:*
LISTEN 2167/named
tcp 0 0 10.10.0.254:5432 0.0.0.0:*
LISTEN 1635/postgres
tcp 0 0 127.0.0.1:5432 0.0.0.0:*
LISTEN 1635/postgres
tcp 0 0 127.0.0.1:953 0.0.0.0:*
LISTEN 2167/named
tcp 0 0 127.0.0.1:5432 127.0.0.1:59125
ESTABLISHED 27198/postgres: ast
tcp 0 0 127.0.0.1:59125 127.0.0.1:5432
ESTABLISHED 27158/asterisk
udp 0 0 0.0.0.0:5060 0.0.0.0:*
27158/asterisk
udp 0 0 127.0.0.1:41958 127.0.0.1:41958
ESTABLISHED 1635/postgres
*udp 0 0 0.0.0.0:40895 <http://0.0.0.0:40895>
0.0.0.0:* 12116/dhcpd*
udp 0 0 10.10.0.254:53 0.0.0.0:*
2167/named
udp 0 0 127.0.0.1:53 0.0.0.0:*
2167/named
*udp 0 0 0.0.0.0:67 <http://0.0.0.0:67>
0.0.0.0:* 12116/dhcpd*
udp 125440 0 0.0.0.0:68 0.0.0.0:*
10681/charon
udp 0 0 10.10.0.254:123 0.0.0.0:*
1290/ntpd
udp 0 0 127.0.0.1:123 0.0.0.0:*
1290/ntpd
*udp6 0 0 :::39873
:::* 12116/dhcpd*
I will try to change grubconf.
But I turned off IPv6 completely by sysctl.d.
With wishes of many good things.
Post by Nicolas C.
Post by CpServiceSPb .
I have isc-dhcp-server installed at ubuntu 14.04 x64.
Its version is 4.2.4
I have fully disabled IPv6 at OS.
Also I have "-4" option for dhcp server startup.
But there is one IPv6 listened address by netstat -anupt.
Port is dyynamic.
What is this dynamically defined port intended for ?
And how is to fully disable IPv6 listening ?
Hello,
What makes you think that this is caused by the DHCP server? Can you give
us the output of your "netstat" command? Is the dhcpd service listening to
an IPv6 address? Maybe a "ps -ef | grep dhcpd" will give us a hint.
Try disabling IPv6 by adding "ipv6.disable=1" on the
GRUB_CMDLINE_LINUX_DEFAULT variable in the /etc/default/grub file, then run
"update-grub" and reboot. But there's little chance that the DHCP server
has anything to do with your problem because it is not dual-stack : it can
operate only for one protocol at the time (DHCPv4 *or* DHCPv6).
Have a nice day,
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