Avamar: Backup failure because DNS query cost - avtar FATAL <8941>: Onhandig serververbindingsprobleem, initialisatie afgebroken. Controleer het juiste serveradres en de aanmeldingsreferenties.

Summary: Het doel van dit KB-artikel is om het speciale scenario uit te leggen waarin de avtar-handshake mislukt, maar de ping werkt en de vereiste TCP-poortnummers ook open zijn.

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Symptoms



In dit scenario ontdekten we dat sommige klanten werden getroffen, terwijl andere dat niet waren.
Voor de getroffen client doet het probleem zich voor met zowel Win FS-back-ups als VSS-back-ups.

Uit de avtar-logboeken kunnen we de volgende foutmelding zien: 
avtar FATAL <8941>: Fatal server connection problem, aborting initialization. Verify correct server address and login credentials.
avtar Info <5694>: - Failed initial handshake, trying again
avtar Info <5562>: - - Connect: Trying 10.xx.xx.xx:29000
Adding log debugging we can see the extra bit of information in the log:


[avtar]  sslcertificate::verify_certificate_ip CN Name='Avamar Server RSA TLS'
    [avtar]  sslcertificate::verify_cnname Performing CN Name validation for Avamar Server RSA TLS
    [avtar]  uwrapper::gethostbyaddr DnsQuery(dns)  returned (9002) for 10.xx.xx.xx
    [avtar]  sslcertificate::verify_certificate_ip CN Name='<avamar-server-fqdn>'
    [avtar]  sslcertificate::verify_cnname Performing CN Name validation for <avamar-server-fqdn>
    [avtar]  uwrapper::gethostbyaddr DnsQuery(dns)  returned (9002) for 10.xx.xx.xx
    [avtar]  sslcertificate::verify_certificate_ip CN Name field did not match Hostname - Checking SA Names
    [avtar]  sslcertificate::verify_certificate_ip rawIPAddrLen = 4
    [avtar]  sslcertificate::verify_certificate_ip Comparing 10.xx.xx.xx with 10.xx.xx.xx
    [avtar]  sslcertificate::verify_certificate_ip Certificate successfully verified
    [avtar]  <-- SSL
    [avtar]  <-- TLS 1.2 Handshake, ServerHelloDone
    [avtar]  --> SSL
    [avtar]  --> TLS 1.2 Handshake, ClientKeyExchange
    [avtar]  --> SSL
    [avtar]  --> TLS 1.2 ChangeCipherSpec
    [avtar]  --> SSL
    [avtar]  --> TLS 1.2 Handshake, Finished
>[avtar]  sslsockimpl::open  connect failure  (setrslt 1)  (conrslt 0)
>[avtar]  Printing ssl error stack
    [avtar]  certlock::~certlock() success to remove SSL cert lock 'C:\Program Files\avs\etc\.tmp\.certlock'
    [avtar]  sslsockimpl::save_server_cert saving cert='C:\Program Files\avs\etc\servercert.pem'
    [avtar]  sslsockimpl::save_server_cert cipher='AES256-SHA'
>[avtar]  sslsockimpl::open  failure
> avtar Info <5694>: - Failed initial handshake, trying again
For the troubleshooting purpose we checked and confirmed that the TCP ports 28001, 28002, 27000 and 29000 were all open and within the correct TCP directions as per Avamar security guide, ping and DNS resolution were also working fine.



 

Cause

Dit probleem is te wijten aan de lange reactietijd in de DNS-query's, in feite kunnen we zien dat de "DnsQuery(dns) geretourneerd" elke keer meer dan 10 seconden duurde, merk op dat het handshake-proces een aantal querypogingen uitvoert voordat het volledig mislukt.

Als voorbeeld: 
2019/03/05-10:22:41.39299 [avtar]  sslcertificate::verify_cnname Performing CN Name validation for Avamar Server RSA TLS
2019/03/05-10:22:53.30100 [avtar]  uwrapper::gethostbyaddr DnsQuery(dns)  returned (9002) for 10.xx.xx.xx
And the entire handshake process would require about 50 seconds to complete and fail:


2019/03/05-10:22:14.89800 [avtar]  sslsockimpl::open  initclient success
....
2019/03/05-10:23:05.41599 [avtar]  sslsockimpl::open  failure

For comparison here is an example from a working client where we see that the the "DnsQuery" is returned in less than 1 second:

2019/03/05-11:56:06.97600 [avtar]  sslcertificate::verify_cnname Performing CN Name validation for <avamar-server-fqdn>
2019/03/05-11:56:07.79600 [avtar]  uwrapper::gethostbyaddr DnsQuery(dns)  returned (9002) for 10.xx.xx.xx
And the entire handshake process would complete in about 13 seconds:


2019/03/05-11:55:54.12400 [avtar]  sslsockimpl::open  initclient success
...
2019/03/05-11:56:07.82899 [avtar]  sslsockimpl::open  initclient success, cipher: AES256-SHA
In a summary, the root cause is identified as DnsQuery spent too much time on the affected client machines.

Resolution

Om dit soort problemen op te lossen, moet de systeembeheerder actie ondernemen op de DNS-server om deze vertraging op te lossen.

Aangezien het probleem buiten het bereik van het Avamar back-upproduct valt, moet de systeembeheerder worden ingeschakeld.

Additional Information

Als u dezelfde fouten ervaart, maar in uw geval de DNS in minder dan een seconde resolveert, ondervindt u mogelijk een ander soort probleem.
Raadpleeg eerst de Dell EMC Knowledge Base om te zien of een ander KB-artikel u kan helpen dit probleem op te lossen, of neem anders contact op met het Avamar-supportteam.

Affected Products

Avamar

Products

Avamar, Avamar Client for Windows
Article Properties
Article Number: 000055434
Article Type: Solution
Last Modified: 11 Oct 2024
Version:  3
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