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sathish_2826's avatar
sathish_2826
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Feb 10, 2016

Round robin LB set, but?

HI,

 

I have a GTM pool with two servers and round robin is the load balancing method, and servers are marked available,

 

When i try nslookup i am getting resolved to both the IP's in an alternate fashion, but while pinging the URL i am only getting the same ip even if i try for 10 times..

 

Could some one clarify me?

 

4 Replies

  • Your described configuration should result in ping getting round-robin results, as you would expect, and that's certainly what I see in my GTM lab with a wideip pointing to a gtm pool with two members in it.

    Perhaps when you do the nslookup, are you setting the DNS server to the GTM, but when you use ping, you're using your system DNS cache ? If you're using windows, try disabling the DNS Client service while testing things.

    You can also run 'tcpdump -nn -i0.0 udp and port 53' on the GTM to verify that when you use ping, DNS queries really are arriving at your GTM, and not being cached somewhere

    You should see something similar to this:

    [root@gtm-1151-181:Active:Standalone] config  tcpdump -nn -i0.0 udp and port 53
    tcpdump: verbose output suppressed, use -v or -vv for full protocol decode
    listening on 0.0, link-type EN10MB (Ethernet), capture size 96 bytes
    00:30:24.322351 IP 172.16.219.11.54636 > 172.16.181.1.53:  42072+ A? www.example.com. (33)
    00:30:24.322435 IP 172.16.181.1.53 > 172.16.219.11.54636:  42072*- 1/0/0 A 172.16.181.112 (49)
    
  • Hello

    If your application is Internet facing you can try using as a test client a DNS Propagation Checker like https://www.whatsmydns.net/

    Also from your F5 cli you can test against Google DNS with this command:

    dig @8.8.8.8 yoururl.com
    (that is if your F5 has outbound DNS access)