Choosing the optic for an ADVA FSP 150-GE102Pro handoff into an RB4011iGS+ SFP+ cage
I do small business installs, and this one is a fibre service handed off on an ADVA FSP 150-GE102Pro. The customer wants the WAN terminated on their own router instead of the carrier box, so it has to land in the SFP+ cage of a MikroTik RB4011iGS+. Nobody told me what fibre the service actually runs on, and the demarc was fitted by the carrier's engineer long before I was involved.
- CPE: MikroTik RB4011iGS+, WAN on sfp-sfpplus1, with a spare 1G single-mode SFP out of the van in the cage - a guess, not a choice
- Carrier demarc: ADVA FSP 150-GE102Pro, LC duplex populated on the service port
- Service: 1 Gbit/s, no media converter in between
- Patch: short LC-LC duplex, whatever was in the cabinet
Where it stands now:
RB4011 sfp-sfpplus1 : link down, rx/tx counters at 0
ADVA FSP 150-GE102Pro : service port LED lit, port 3 looks like a combo (RJ45 + cage)What I have already done:
- swapped the LC patch cord and cleaned both ends
- swapped tx/rx on the RouterBoard side
- read the demarc front panel, for what it is worth: that lit LED only tells me the port is powered and enabled, and with no management access to the ADVA I cannot see whether it is sitting on a receive alarm
So two questions before I order the right part. How do I establish whether the carrier is delivering single-mode or multimode without guessing, and for a 1 Gbit service is it safer to put a palin 1G SFP into that SFP+ cage or an SFP+?
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Comments 2
Do not order anything yet. Open the ADVA, pull the module the carrier put in it and read the label - the carrier decides the fibre type, you only have to match it. If the print is unreadable in a dark cabinet, the latch colour is a decent first guess: single-mode modules are usually blue, multimode ones black.
More often than not on these business handoffs it turns out to be a plain LC multimode optic, and then what you want on the RouterBoard is a 1000BASE-SX plus a multimode patch cord, not the single-mode part sitting in that cage now.
On the cage question: use a 1G SFP. An SFP+ will seat and the port will accept it, but for a 1 Gbit handoff a 1G module gives you the best chance of the port training cleanly, and a 10G part buys you nothing here.
While you are in that router - MikroTik's own documentation for the RB4011 lists passive DAC and SFP GPON modules as not supported, so do not plan anything clever for that cage later on.
And you are right about port 3 on the FSP 150 being a combo, so RJ45 is a usable fallback if the fibre pairing turns into a fight.
The boring rule that catches people out here: SR-type optics run at 850 nm over multimode, LR-type at 1310 nm over single-mode, and both ends of a link have to be the same type. A fibre mismatch is not something you fix on one side only.
We hit it in the other direction on a pair of SRX3600 - SRX-SFP-10GE-LR turned up in the box instead of SRX-SFP-10GE-SR for links that were three metres long inside the same room. That part is fine, the distance on the label is a maximum and not a minimum, you just need single-mode patch cords at both ends. The reverse, running an LR module over multimode, is the one to avoid: it may light up on a very short run, but it is out of specification and you will not enjoy chasing it six months later.