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MB_271724's avatar
MB_271724
Icon for Nimbostratus rankNimbostratus
Feb 09, 2017

LTM delay with AAAA record request over IPv4?

I have an LTM running 11.5.3 that seems to be causing a delay when a RedHat6 server makes a combined AAAA/A request over IPv4 (only) to a DNS server pool being load-balanced by the LTM. There's a FastL4 udp profile in place (no DNS profile). This is not a problem with an old ACE30 load-balancer; only with the LTM. Anyone have any suggestions about how to deal with this? Documentation refers quite a bit to IPv6-to-IPv4 traffic manipulation but nothing that I could find concerning a combined A/AAAA request over IPv4. Apparently the AAAA request always goes first and sometimes a AAAA record can be returned and sometimes it's an A record (simply based on what's available for that lookup). Not sure if the v6-to-v4 settings apply in this situation since there's no actual v6 traffic.

 

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LTM

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  • Kai_Wilke's avatar
    Kai_Wilke
    Icon for MVP rankMVP
    Feb 09, 2017

    Hi MB,

     

    if you don't apply a DNS profile to your Virtual Server, your F5 wouldn't care about A, AAAA or even combined A & AAAA queries. Only the payload size of the DNS query / response would matter in this case...

     

    Have you already captured the ingress / egress traffic of your F5 to see if the F5 quickly forwards the DNS request/responses and/or if the client eventually tries to use DNS-over-TCP and needs to wait for TCP timeouts (e.g. DNS payload >= 512 bytes)?

     

    Cheers, Kai