Router question

[britechguy]

For small businesses, before broadband, we used to use multi WAN dial up routers....like WebRamp, and some 3COM Office connect products. They'd employ multiple 56k modems to connect an office network.

The following is not meant to be dismissive, as I remember those days, but they're absolutely, positively irrelevant to now. And my presumption, and perhaps it was incorrect, is that we were talking about equipment that's commonly used now and no more than approximately 10-15 years old (if that).

I'll revise my statement to I have not dealt with any recently available modem-router-gateway made in probably the last 20 years that hasn't handled LAN traffic just fine if connectivity to the internet is interrupted for reasons beyond its control.

 

[NETWizz]

Most commercial implementations are grossly more complex. Typically they run DNS on Active Directory as well as their own DHCP services that rarely come from network devices. That said, networking actually gets grossly more complex.

Most cores have hundreds of subnets generally variably sub netted with a multitude of subnets and masks, but it is all still routing and switching for the most part. That said there are a LOT of abstraction layers like vxlan, l2tpv3, pseudo-wire stuff, etc.

It is commonplace to run a virtual interface from one device to another over a routed network or stretch a VLAN over a routed network, or to do a multipoint DMVPN tunnel etc. You haven't lived as a network engineer until you have troubleshooted an issue with broken TCP connections over a large enterprise network with BGP, MPLS, various points of asymmetric routing, etc. Solving this issue you are experiencing would be cake; in fact, you could likely easily isolate the likely cause without taking it down by checking how it is put together.

 

[YeOldeStonecat]

I went to the customer site I mentioned earlier and it turns out their description of the problem doesn't do justice to the actual problem (surprise, surprise!). They have deeper problems with their POS software which seems to be really flakey with losing printers and things. The actual LAN seems to be running fine. The modem could be flakey, hard to tell at this point, it was stable the whole time I was there. So I'll deal with the software issues first and then see where we stand.

I was wondering what you meant by no LAN function. I'm sure most here, from what I'm reading, are just assuming basic IP connectivity to other LAN resources like printers, etc. Or perhaps just a mapped drive to another workstation. Yeah those should always keep running, as the multiple ETH ports on a common broadband router/gateway is just bridged ports to make a switch.

 

[britechguy]

I'm sure most here, from what I'm reading, are just assuming basic IP connectivity to other LAN resources like printers, etc.

That's certainly what I was thinking. Devices on the LAN normally able to communicate with each other still communicate with each other in the absence of a connection to the internet.

 

[Sky-Knight]

That's certainly what I was thinking. Devices on the LAN normally able to communicate with each other still communicate with each other in the absence of a connection to the internet.

As long as the device that's handing them IP information is still doing so. I've seen a few cases where these all in wonder routers the ISPs put out lock up. And when they do the internal switch fails to function, much less anything else.

But these events are not common, and represent a new failure mode not some sort of normal we should be tolerating.

but yeah, I learned a long time ago never to trust "the internet is down" from any source... anywhere. It's just too vague of a symptom to use for anything useful.

 

[fincoder]

In my case I assume the ISP-modified firmware in the residential modem/router/gateway simply has a bug. They likely get few complaints because the vast majority of mum & dad users don't do peer-to-peer, it would also be difficult for the ISP helpdesk to diagnose, so it was never resolved.

One day I'll check if it's a DNS issue or if the LAN really is down. I'm positive the DHCP clients have the DNS set to the gateway IP.