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eqiad: upgrade row C and D uplinks from 4x10G to 1x40G
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Description

With the new eqiad MPC7E linecards (see T304712)

And the work done in T308331: eqiad: move non WMCS servers out of rack D5, we now have the capacity to run a single 40G link from row C and D to the core routers.

This will bring multiple benefits:

  • Improve performance and help improve T291627: Packet Drops on Eqiad ASW -> CR uplinks (right now two large flows being balanced on the same 10G link can cause packet drops)
  • Standardize LACP bundles (right now the 4 links end on multiple linecards and both spines (fpc2/fpc7), more explicit failure scenarios
  • Clean up cabling (remove 12 fibers running across the cage)
  • Clean up switch/router config (less interfaces, no need for bandwidth-threshold knobs)
  • Anticipate link move from old 10G linecards to new 40/100G

The main downside being:

  • Discrepancies between rows A/B and C/D, which is weak compared to the benefits. Those rows are already different anyway as they have less prod racks