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May 27, 2014

domain has no valid mail exchangers

Filed under: Linux — Tags: , , , , , — admin @ 8:33 pm

Today I face a strange problem with e-mail won’t be deliver, to a client . I have tested from yahoo, gmail and other service and everything was fine however one client from gmx was complain that he can’t send e-mail to that account

A message that you sent could not be delivered to one or more of
its recipients. This is a permanent error. The following address
failed:

“user@domain.com”:
domain has no valid mail exchangers

So, first impresion was to check if domain.com have a mx . So a short
dig mx domain.com output a

DiG 9.8.2rc1-RedHat-9.8.2-0.23.rc1.el6_5.1 mail.domain.com
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- ;; flags: qr rd ra; QUERY: 1, ANSWER: 2, AUTHORITY: 2, ADDITIONAL: 0 ;; QUESTION SECTION: ;domain.com. IN MX ;; ANSWER SECTION: domain.com. 2011 IN MX 10 mail.domain.com.

So it appear that is there.
But the problem was when I query to see who is the mail.domain.com

dig mail.domain.com

DiG 9.8.2rc1-RedHat-9.8.2-0.23.rc1.el6_5.1 mail.domain.com
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- ;; flags: qr rd ra; QUERY: 1, ANSWER: 2, AUTHORITY: 2, ADDITIONAL: 0 ;; QUESTION SECTION: ;mail.domain.com. IN A ;; ANSWER SECTION: mail.domain.com. 1937 IN CNAME domain.com. domain.com. 1937 IN A xxx.xxx.xxx.xx ;; AUTHORITY SECTION: domain.com. 1932 IN NS dns1.domain.com. domain.com. 1932 IN NS dns2.domain.com. ;; Query time: 3 msec

So we see that mail.domain.com is a CNAME, it appear that is against rfc , and need to be A zone and not alias/CNAME.
So the solution is to modify mail.domain.com to be A xxx.xxx.xxx.xxx

Regards

September 11, 2012

putty slow to connect – SSH

Filed under: Linux — Tags: , , , , , — admin @ 10:56 am

Hello
Today , I was trying to connect to one of my server and observe that after I introduce user/password I don’t enter immediately on log on. It take some time to reach at command promt.

Well first of all I think this may happen when you have load on a server, however my server was fine, so what other reason should can be ?
Well I try to make a nslookup on my ip and this was resolved. So I have a reverse ptr.
Well I updated the resolv.conf with google nameserver and the problem disappear .

So basically just add at the beginning of /etc/resolv.conf the line bellowl:

nameserver 8.8.8.8

Part 2:
Waiting for SSH login prompt
It seems that the problem still persist. So , i try from a linux server
ssh -vvv ip_of_server
and did notice this
debug1: Unspecified GSS failure. Minor code may provide more information
No credentials cache found
debug1: Unspecified GSS failure. Minor code may provide more information
No credentials cache found
debug1: Unspecified GSS failure. Minor code may provide more information
debug2: we did not send a packet, disable method

Ok, now I check the /etc/ssh/sshd_config and see that
GSSAPIAuthentication yes
SSAPICleanupCredentials yes

are both on yes. I disable them and now everything is ok.

Part 3
You may use also into /etc/ssh/sshd_config
UseDNS no

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