I can hear it pinging and talking, but it can't hear anything

Question

I got one-way connectivity to some devices and sometimes(randomly) no connectivity, with odd link-status LED lighting.

There are 1 PC(mine) and 2 routers('A' and 'B') connected to a switch(unmanaged) and 2 more PCs behind router 'B'. My PC and router 'A' are fine seeing each other, but we can't ping router 'B' or PCs behind it(nor any other sort of connectivity).

But strange is, Wireshark shows me the other PC's ping request reaching mine and mine replies, but the other PC says "timed out". All devices have static IPs in the same subnet assigned to them.

More details:

The switch's link-status LED for the cable to router 'B' has some strange behaviors:

1. It is sometimes off, despite router 'B' is always on. I noticed when it gets on, people are working with the unconnected PCs behind router 'B'.

2. I could see the one-way ping requests, but the LED was lighting for a second then off for more than two(I'm not sure if it's the 'Idle Connection' lighting or not).

Also, in Wireshark sometimes I see router 'B' sending RIP responses and other devices introducing themselves and etc., but sometimes not.

Routers' LAN ports are used and their RIP setting is both set to RIPv1. Both routers and the switch are consumer-level devices(Just in case somebody wants to question their implementations of network protocols). Routers are actually ADSL Modem Routers. Both routers are updated to their latest firmware.

Everything was working fine before I replaced router 'A' with the switch, but now getting router 'A' back to the place didn't solve the problem! Also tested connecting cable from router 'B' directly to my PC with no light and no luck.

EDIT:

Because of random and odd connections, I thought maybe there is a non-software issue involved. The cable between the switch and router 'B' is a CAT6 SFTP which has about 100 m length(50 m per EDIT 3), which is quite usual for CAT6, but I thought if the cable has occasionally much of electromagnetic fileds, could it somehow create these strange behaviors?

EDIT 2:

Is there any necessity to use T568A for the "twisted pairs" to work correctly? I've just used the same order of colors for both ends without attention to T568A (and as I said, it had worked well for some time).

EDIT 3:

I patched it using T658A and nothing changed, including strange behaviors!

At first, both LEDs was off, so I thought I've messed the jacks up, but when I replaced the switch with router 'A', it's LED got fully on, with LED on router 'B' still off! And Wireshark showed nothing.

Today, without any action, it got exactly like before: switch's LED was lit, Wireshark showed some broadcasts coming from router 'B' and the PCs behind it, and still they can't hear me pinging them.

I noticed the RIP responses of router 'A' and 'B' are being broadcasted quite beside each other, each one repeating it after the other router, for about 3-4 times, then they're silent for some seconds, where several other communications by other devices do happen.

(And I was wrong about the length. The operators said it's just 50 meters.)

Thanks for the responses.

Answer 1

Arrggghhhh! it was the jack! The jack's size made it a very little bit loose in router 'B'. How much unexpected! It was only when I tried to cross-check the routers that I noticed I have to wrestle with the jack to make it's link-status LED lit.

But how could it cause the one-way connection? Interesting ...

Thanks everybody for helping.

Answer 2

Yes, it's quite important to use the T568A (or B) wiring schemes for reliable ethernet performance. Unshielded Twisted Pair cables are only able to reliably carry high-speed signals at full-duplex for distances up to 100 m when specific wires are selected: For 100BASE-TX, The four wires that are not transmitting signals are just as important as the four that are: They serve as shielding to prevent cross-talk, interference. echos, and fade. For 1000BASE-T*, all four pairs are used, but it's still important to separate wires carrying certain signals from others that might be carrying signals that would create destructive or constructive interference on neighbouring wires.

For short cables, at lower line rates, it's quite possible to 'get away' with non-standard wiring, but as distances approach the specification limits, and the fastest line rates, selecting the proper pairs to send, receive, and dampen signals becomes more critical.

So, if you're not using one of the specified cabling pinouts, then your connection will be unreliable. This may manifest in intermittent connectivity, one-way transmission problems, pattern sensitivity, etc.

Answer 3

Your second router has a firewall and/or NAT enabled which prevents anything originated on the WAN side from reaching the LAN side.

You probably just want to set it up as a bridge so that you have a single LAN.