LDAP - DNS/Hosts lookup failed

[Sören Busse]

Hi,


we're using the isc-dhcp-server in our enviroment, but since the version 4.3 there is an issue with the domain lookup.

We've defined multiple domains in /etc/hosts e.g ldapm.foss-cloud.int or foss-cloud.org.


The problem is now that we get an "Can't contact LDAP server" error, altough the domains are pointing to 127.0.0.1.

So I've done a tcpdump which shows that the DHCP server tries to make requests to an external ip, which is the A-Record of foss-cloud.org

02:11:05.373307 IP 192.168.5.101.46016 > 62.204.105.153.636: Flags [S], seq 3665195687, win 29200, options [mss 1460,sackOK,TS val 2152987841 ecr 0,nop,wscale 7], length 0
02:11:06.396480 IP 192.168.5.101.46016 > 62.204.105.153.636: Flags [S], seq 3665195687, win 29200, options [mss 1460,sackOK,TS val 2152988148 ecr 0,nop,wscale 7], length 0
02:11:08.529804 IP 192.168.5.101.46016 > 62.204.105.153.636: Flags [S], seq 3665195687, win 29200, options [mss 1460,sackOK,TS val 2152988788 ecr 0,nop,wscale 7], length 0
02:11:12.583127 IP 192.168.5.101.46016 > 62.204.105.153.636: Flags [S], seq 3665195687, win 29200, options [mss 1460,sackOK,TS val 2152990004 ecr 0,nop,wscale 7], length 0
02:11:20.689774 IP 192.168.5.101.46016 > 62.204.105.153.636: Flags [S], seq 3665195687, win 29200, options [mss 1460,sackOK,TS val 2152992436 ecr 0,nop,wscale 7], length 0

And this happens altough foss-cloud.org points to 127.0.0.1 in /etc/hosts.

If I now try a domain which points to 127.0.0.1 for example localtest.me, the DHCP server connects without any issues.


Now there is the question how to solve this issue?


For more information here is also a thread on the gentoo forum, where I've put some more details:

https://forums.gentoo.org/viewtopic-p-8079698.html#8079698


Kernel: Linux localhost 4.10.1-gentoo


Kind regards

Sören Busse
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