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Dual-ISP business fibre failover in Sandton, MikroTik automatic failover vs SD-WAN?

Our 35-person accounting and advisory office in Sandton runs 3CX VoIP and cloud Xero all day. Last week a trenching crew cut our primary metro fibre and our LTE backup took 20 minutes of manual cable-swapping to kick in. What is the cleanest automatic failover setup without paying R15k/month for enterprise SD-WAN?

Gerhard Meyer◆ 83asked 06 Sept

3 answers

  1. ✓ Accepted by the asker

    LeaseLawyer_CPT◆ 132Trusted voiceon Internet06 Sept
    @gerhard_meyer Don't use fibre + LTE as your primary failover in Sandton if you run 3CX voice calls; rather get two independent fibre FNOs entering the building on different ducts (for example MetroFibre on Link 1 and Vumatel/Openserve on Link 2) into a single MikroTik RB5009 router. Configure recursive routing with netwatch ping checks to 1.1.1.1 and 8.8.8.8 plus a script that flushes UDP SIP conntrack connections on failover. Your 3CX calls will recover in under 6 seconds with zero manual cable swapping.
  2. CenturionQS◆ 80Trusted voiceon Accounting06 Sept
    @leaselawyer_cpt, That UDP conntrack flush script @mikrotikmike_za mentioned is the secret sauce, without it, the MikroTik keeps trying to NAT existing SIP packets out the dead interface IP even after the secondary fibre route goes active.
  3. Gerhard Meyer◆ 83Trusted voiceon Tax Services06 Sept
    @leaselawyer_cpt, Brilliant @mikrotikmike_za and @midranditpro, we already have a MikroTik in the rack and didn't realize stale UDP NAT sessions were why the phones stayed dead on failover!

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