Forum Discussion

Nimbostratus

Aug 03, 2015

Curl perform failed: Couldn't resolve host name (6)

Hi all, can anyone give me a hint on what causes this error ? Can't find anything on DC /internet search HTTP module: authenticateUser(): Curl perform failed: Couldn't resolve host name (6)...

Hannes_Rapp

Nimbostratus

Aug 03, 2015

To sort out the DNS issues, try to follow the steps below:

 Check to see if you have a DNS server configured
hannesr@(lb01)(cfg-sync Changes Pending)(Active)(/Common)(tmos) list sys db dns.nameservers
sys db dns.nameservers {
    value "10.199.22.2 10.199.22.6"
}
hannesr@(lb01)(cfg-sync Changes Pending)(Active)(/Common)(tmos) q

 Check to see if you have DNS server connectivity
[hannesr@lb01:Active:Changes Pending] config  dig blabla
; <<>> DiG 9.9.6-P2 <<>> blabla
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NXDOMAIN, id: 58826
;; flags: qr rd ra; QUERY: 1, ANSWER: 0, AUTHORITY: 1, ADDITIONAL: 1

;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 4096
;; QUESTION SECTION:
;blabla.                IN  A

;; AUTHORITY SECTION:
.           10688   IN  SOA a.root-servers.net. nstld.verisign-grs.com. 2015080300 1800 900 604800 86400

;; Query time: 1 msec
;; SERVER: 10.199.22.253(10.199.22.2)
;; WHEN: Mon Aug 03 12:08:38 UTC 2015
;; MSG SIZE  rcvd: 110

Hannes_Rapp
Nimbostratus
Aug 03, 2015
1) If you don't have a DNS server configured - configure one. 2) If you don't receive any response to dig command - make sure you have UDP/53 connectivity to the DNS server. 3) If both commands succeed, assume that DNS on F5 is OK and you must update the DNS server's configuration to include a new A entry for your service name. When done, retry your cURL command. Good luck!
NN_210021
Nimbostratus
Aug 03, 2015
So heres the outcome: sys db.nameservers { value "10.128.20.252 10.128.128.1.243" } for the dig command: ; <<>> DiG 9.9.5 <<>> blabla ;; global options: +cmd ;; Got answer: ;; ->>HEADER<<- opcode: QUERY, status: SERVFAIL, id: 62411 ;; flags: qr rd ra; QUERY: 1, ANSWER: 0, AUTHORITY: 0, ADDITIONAL: 1 ;; OPT PSEUDOSECTION: ; EDNS: version: 0, flags:; udp: 4000 ;; QUESTION SECTION: ;blabla. IN A ;; Query time: 29 msec ;; SERVER: 10.128.1.24353(10.128.1.243) ;; WHEN: Mon Aug 03 14:25:38 UTC 2015 ;; MSG SIZE rcvd: 35
Hannes_Rapp
Nimbostratus
Aug 03, 2015
DNS config on your F5 is in place. Furthermore, you don't have any connectivity problems to a DNS server. What is the outcome if you issue the command "host YourServiceName" ? Replace YourServiceName with the actual name you're using in the cURL command.
NN_210021
Nimbostratus
Aug 03, 2015
That SERVFAIL seems strange or is it ok ? For example curl http://textbelt.com results in curl: (6) Couldnt resolve host 'textbelt.com' Same for google.
Hannes_Rapp
Nimbostratus
Aug 03, 2015
We can then conclude that your DNS server (10.128.1.243) is missing the configuration to resolve "textbelt.com" to an IP-address, or has another problem. I don't think it's an F5 (configuration) issue by any means.
NN_210021
Nimbostratus
Aug 03, 2015
So at least the F5 is ok. I'll check the DNS server. Thanks for your help and guidance, well done !
Amresh008
Nimbostratus
Aug 10, 2018
There are two ways in which DNS can be added in F5 and both have different results. If you add it under system tab - that helps your F5 (bash) to resolve the hostname for cURL And if you add it under Network- DNS resolver list,this enables your TMM to resolve the URLs (used in http proxy config.)