topic Re: Connect unmanaged Netgear Switch to HP J9728A 2920-48G in Switches, Hubs, and Modems

Connect unmanaged Netgear Switch to HP J9728A 2920-48G

sd219 — Tue, 21 Apr 2020 12:26:10 GMT

Hey!

In our network some guys recently plugged in the cable of a network jack in an unmanaged 8-port Netgear switch.

So Basically there is an existing connection between Port 3 of the HP J9728A 2920-48G Switch and the unmanaged 8-port Netgear switch right now.

On our HP Switch, STP is enabled and i guess thats why i got notifications at the Switch Web Client like "port 3 is Blocked by STP"

So right now it is not possible to reach the hardware via icmp or something else which is connected to the unmanaged switch, whereas i am located in the conventionally network behind the HP Switch.

I guess that this behaviour should be completely right as it acts right now.

So my question is technically:

Why does this specific connection between the managed HP Switch and the unmanaged Netgear switch not work?

Why i am not able to reach the respective hardware behind the unmanaged switch and what should i do to solve the problem? ( maybe just use another HP managed switch instead of the rubbish netgear switch, which is actually not possible right now) or is it just a software configuration issue?

Re: Connect unmanaged Netgear Switch to HP J9728A 2920-48G

parnassus — Wed, 22 Apr 2020 00:31:10 GMT

Hi! on your HP 2920 please execute the commands reported below:

show running-config interface ethernet 3
show spanning-tree ethernet 3
show spanning-tree ethernet 3 detail
show spanning-tree ethernet 3 config

and paste here their outputs (sanitized = MAC Addresses obfuscated) using the "Insert/Edit code sample" </> customizing icon above for easy reading.

It's totally possible that you have a (STP related) running configuration that protect your port 3 when another switch is connected or that your connected unmanaged switch is hiding a loop that your HP 2920 is able to diagnose (and it is configured to protect itself in such a scenario).

Re: Connect unmanaged Netgear Switch to HP J9728A 2920-48G

sd219 — Wed, 22 Apr 2020 11:06:20 GMT

Switch-1-1-1# show running-config interface ethernet 3 Running configuration: interface 3 unknown-vlans block tagged vlan 1001-1004,1006,1008-1011,1013-1018,1029-1032,1034,1047-1051,1196,1201-1202 untagged vlan 1 loop-protect exit Switch-1-1-1# show spanning-tree ethernet 3 Multiple Spanning Tree (MST) Information STP Enabled : Yes Force Version : RSTP-operation IST Mapped VLANs : 1-4094 Switch MAC Address : xxxxxx-yyyyyy Switch Priority : 32768 Max Age : 20 Max Hops : 20 Forward Delay : 15 Topology Change Count : 5 Time Since Last Change : 16 days CST Root MAC Address : xxxxxx-yyyyyy CST Root Priority : 0 CST Root Path Cost : 2000 CST Root Port : A1 IST Regional Root MAC Address : xxxxxx-yyyyyy IST Regional Root Priority : 32768 IST Regional Root Path Cost : 0 IST Remaining Hops : 20 Root Guard Ports : Loop Guard Ports : TCN Guard Ports : BPDU Protected Ports : BPDU Filtered Ports : PVST Protected Ports : PVST Filtered Ports : Root Inconsistent Ports : Loop Inconsistent Ports : | Prio | Designated Hello Port Type | Cost rity State | Bridge Time PtP Edge ----- ---------- + --------- ---- ------------ + ------------- ---- --- ---- 3 100/1000T | 20000 128 Forwarding | xxxxxx-yyyyyy 2 Yes Yes Switch-1-1-1# show spanning-tree ethernet 3 detail Status and Counters - CST Port(s) Detailed Information Port : 3 Status : Up BPDU Protection : No BPDU Filtering : No PVST Protection : No PVST Filtering : No Errant BPDU Count : 0 Root Guard : No Loop Guard : No TCN Guard : No MST Region Boundary : Yes External Path Cost : 20000 External Root Path Cost : 2000 Administrative Hello Time : Global Operational Hello Time : 2 AdminEdgePort : No Auto Edge Port : Yes OperEdgePort : Yes AdminPointToPointMAC : True OperPointToPointMAC : Yes Aged BPDUs Count : 0 Loop-back BPDUs Count : 0 TC ACK Flag Transmitted : 0 TC ACK Flag Received : 0 MST MST CFG CFG TCN TCN BPDUs Tx BPDUs Rx BPDUs Tx BPDUs Rx BPDUs Tx BPDUs Rx ---------- ---------- ---------- ---------- ---------- ---------- 0 0 0 0 0 0 Switch-1-1-1# show spanning-tree ethernet 3 config Multiple Spanning Tree (MST) Configuration Information STP Enabled [No] : Yes Force Version [MSTP-operation] : RSTP-operation Default Path Costs [802.1t] : 802.1t Port State Events Logging : Disabled MST Configuration Name : xxxxxx-yyyyyy MST Configuration Revision : 0 Switch Priority : 32768 Forward Delay [15] : 15 Hello Time [2] : 2 Max Age [20] : 20 Max Hops [20] : 20 | Path Prio Admin Auto Admin Hello Root TCN Loop BPDU Port Type | Cost rity Edge Edge PtP Time Grd Grd Grd Flt ---- ---------- + --------- ---- ----- ---- ----- ------ ---- --- ---- --- 3 100/1000T | Auto 128 No Yes True Global No No No No

Re: Connect unmanaged Netgear Switch to HP J9728A 2920-48G

parnassus — Wed, 22 Apr 2020 13:36:25 GMT

Hi, well the port 3 is in Forwarding state...so STP is not blocking that port (actually). I strongly suspect (the reason, from the Unmanaged Netgear switch, was explained here) that the only packet's tagging understood and admitted by the Unmanaged Netgear Switch is indeed the "untagged" one thus the VLAN id 1 you configured the port 3 to be untagged member of; any other packet leaving the port 3 tagged with any of the VLAN ids you have the port 3 configured to be member of (VLAN id 1001-1004, 1006, 1008-1011, 1013-1018, 1029-1032, 1034, 1047-1051, 1196 and 1201-1202 [*]) is going to be dropped on the incoming port of the Unmanaged Switch.

Since you already have RSTP enabled, I suggest you to setup root-guard, bpdu-protection and loop protection on port 3...see here to understand why.

[*] A nice way to easily understand, from the port standpoint, how is the VLAN membership on a particular port (or range) is to use the show vlan port <port-id> detail command.

Re: Connect unmanaged Netgear Switch to HP J9728A 2920-48G

sd219 — Wed, 22 Apr 2020 16:35:25 GMT

So in addition, all the components behind the unmanaged switch are in VLAN 1 and apart from that, the managed HP switch is also in VLAN 1

So concerning your statement "Since you already have RSTP enabled, I suggest you to setup root-guard, bpdu-protection and loop protection on port 3...see here to understand why."

Who do i do that?

Re: Connect unmanaged Netgear Switch to HP J9728A 2920-48G

parnassus — Wed, 22 Apr 2020 23:40:02 GMT

Sorry, do you want to really ask: Why or How I do that? ...I really can't understand the "Who do i do that?" question.

Re: Connect unmanaged Netgear Switch to HP J9728A 2920-48G

sd219 — Thu, 23 Apr 2020 14:42:15 GMT

Sorry, i must have been mentally absent at the time.

Yeah, i want to know, why do i have to do that and especially how, so which commands do i have to use?

Re: Connect unmanaged Netgear Switch to HP J9728A 2920-48G

sd219 — Thu, 30 Apr 2020 14:46:02 GMT

@parnassus Do you have more information for me right now?

Re: Connect unmanaged Netgear Switch to HP J9728A 2920-48G

parnassus — Thu, 30 Apr 2020 21:20:08 GMT

Hello, isn't the content available at the second link I provided you already self-explaining enough?

IMHO that blog entry (in a more discorsive way with respect to what official reference guides are generally able to provide) there is the "Why" (protect your network) against the "Who" (can cause you issues) and the "How" (do that in terms of configuration) specifying the "Where" (you should enforce your protective mechanisms).

Re: Connect unmanaged Netgear Switch to HP J9728A 2920-48G

sd219 — Mon, 04 May 2020 09:15:21 GMT

@parnassus in the meantime I have found out something new.

So the device which is plugged in to the unmanaged switch, is located in the default, untagged VLAN.

So from any device in this VLAN, i am able to reach this device via icmp but if i try to reach the respective device on the unmanaged switch from another vlan, i get back a timeout. So no connection is possible.

So IMHO i guess, i am not able to reach that device from another VLAN because the unmanaged switch didn't tagg the ethernet packet with the expected VLAN ID or pvid ?

Do you have any idea, how i could be able to reach this device from another specific vlan ? Maybe with masquerading or NAT or something else?

Re: Connect unmanaged Netgear Switch to HP J9728A 2920-48G

sd219 — Tue, 12 May 2020 12:16:48 GMT

@parnassus do you have any update to my latest comment?