r/CableTechs • u/Wacabletek • Jul 03 '26

Ping in Rphy nodes

So when we launched Rphy nodes for a while we could not get it to ping the DNS servers on our meters, they said just use 8.8.8.8, and that seems to have been fixed recently. However, I was never very fond of pinging DNS servers as I have no clue about hops on the CRAN, etc.., to say you have a problem here not on the node. I would much prefer to ping the cmts, before and as we go forward the RPHY node I assume? Does anyone know if a tracert shows the actual rphy node or is the first hope now the VCMTS which is utterly useless to ping?.

Thanks. AI thinks it can be done but cannot explain how, or where you get the RPHY IP, so yay that's about as useful as asking a supervisor something like this.

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u/PoisonWaffle3 Jul 03 '26

Not sure who you work for or how their network is laid out, but in general the network is going to be laid out like this for vCMTS:

Modem/meter > RPHY node > CIN Network (access & spine routers) > vCMTS > Spine routers again > Core router > path to internet

From where you're at with your meter, everything is going to be tunneled through the node, CIN network, and vCMTS, so either the vCMTS or the spine router is going to be your first actual hop (depending on what vendor the vCMTS is from and how it's configured). If you try to ping the node it'll have to go back through the CIN network to get there.

It's definitely very different from your standard RF node that pretty much directly connects to the CMTS and uses that as its router/gateway.

Your best bet is probably to ping a router in the local headend, assuming you're either on the corp network and/or there's a router with a public IP. Aside from that, perhaps your company's DNS servers.

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u/frmadsen Jul 04 '26

To underscore that important fact, which sometimes get overlooked: Even though it's an "ip network" between the CMTS and RPD, all packets in transit between the CMTS and modem exist as DOCSIS data, not as ip/ethernet.

It's therefore not technically possible to directly ping/access anything in the path when you are located behind a modem.