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dv-vd
Visitor III
August 29, 2025
Solved

Mixed sd-wan setup: static cable wan ignored when dhcp wans active

  • August 29, 2025
  • 1 reply
  • 327 views

hi everyone,

running fortios 7.4 on fortigate 70g with sd-wan across three wans (all have fixed external IPs):

  • isp1: cable internet (docsis, static config, no dhcp passthrough)

  • isp2 & isp3: two separate 5g connections (fixed external IPs, but dhcp passthrough to the firewall, ip/netmask/gateway set automatically)

the problem:

  • isp2 & isp3 work perfectly — they show dynamic 0.0.0.0/0 routes and are fully used by sd-wan.

  • isp1 needs manual ip/netmask and a static route. it shows “up” in sd-wan but carries no traffic unless both 5g connections are disabled.

  • routing table shows isp2/isp3 dynamic routes at the top, while isp1 sits static and is ignored.

isp1 says enabling dhcp passthrough on their docsis modem is too much work and would break their provisioning, so they won’t change it.

questions:

  • any supported way to make sd-wan handle static-only wan links?

  • any cli tricks to make sd-wan treat that static route like a dhcp one?

  • would upgrading to 7.6 help, or is this just a hard limitation?

need more info or screenshots? happy to share details.

thanks,
sean

    Best answer by Toshi_Esumi

    I think I commented the same recently to another post.
    Static route's default admin distance is 10, while DHCP/PPPoE injected "static" default route's distance is 5 because the default distance on those interface is 5. So you need to either
    1) set static default route's distance to 5, or
    2) set distance on the DHCP/PPPoE interface to 10, which would change those default routes' to 10.

    Toshi

    1 reply

    Toshi_Esumi
    SuperUser
    Toshi_EsumiAnswer
    SuperUser
    August 29, 2025

    I think I commented the same recently to another post.
    Static route's default admin distance is 10, while DHCP/PPPoE injected "static" default route's distance is 5 because the default distance on those interface is 5. So you need to either
    1) set static default route's distance to 5, or
    2) set distance on the DHCP/PPPoE interface to 10, which would change those default routes' to 10.

    Toshi

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