HPE Community read-only access December 15, 2018
This is a maintenance upgrade. You will be able to read articles and posts, but not post or reply.
Hours:
Dec 15, 4:00 am to 10:00 am UTC
Dec 14, 10:00 pm CST to Dec 15, 4:00 am CST
Dec 14, 8:00 pm PST to Dec 15, 2:00 am PST
LAN Routing
cancel
Showing results for 
Search instead for 
Did you mean: 

How to build a triple "ethernet repeater station"?

 
RegTester
Occasional Collector

How to build a triple "ethernet repeater station"?

Hi,

 

I've got three embedded devices which are p2p connected to each other, meaning:

 

A <> B

A <> C

B <> C

 

Now I want to be a "ethernet repeater" between all three connections.

 

A <> me <> B

A <> me <> C

B <> me <> C

 

meaning, that all trafic goes through me. So I can delay, discard or alter the telegrams at my will.

I want to do this because my task is to test the reliabilty, robustness, timing, ... of those three connections.

 

I will use three IP aliases, so that A, B and C will communicate with normal IP-Adresses as before,

but those telegrams will get to me and I decide what to do with those telegrams.

Normally I will send the telegram to the normal destination, as a "ether repeater" would do.

 

I have got a HP 1810-8G and now I want to figure out how to configure the switch.

 

Net1: A and me

Net2: B and me

Net3: C and me

 

A, B and C should not be able to communicate directly with each other,

but me should be able to communicate to A, B and C, depending on their IP-addresses.

Therefor I will propably have to set permanently the correct mac-adresses via

 

arp -s ip-A mac-A

arp -s ip-B mac-B

arp -s ip-C mac-C

 

to assure that the mac-address-based switching will go to the right port of the switch.

If A, B or C sends a telegram he can do this only with the mac address of me, because the arp-telegrams

can only be answered by me.

 

So, if A sends a telegram to B, I will get it, and I will decide if I send it to B or instead to C, delay it, alter it, ...

 

In every Net (1, 2 or 3) my communication partner (A, B oder C) will think he is normally connected and

he communicates with B, C or A.

 

I've tried the task with VLANs but i cannot configure the me-port into three vlans, and if I use an "old school" ethernet hub to "triple me to three ports", I will have every telegramm from me in every single net (1, 2 and 3), which I NOT want.

 

How do I have to configure the 1810 (Trunk, VLAN, tagged/untagged, management port, ...)?

 

Kind regards

 

Martin, hoping you can help me

 

1 REPLY
Vince-Whirlwind
Honored Contributor

Re: How to build a triple "ethernet repeater station"?

The hardest part of what you are trying to do is this:

 

"if A sends a telegram to B, I will get it, and I will decide if I send it to B or instead to C,delay it, alter it, "

 

You might be able to do some of this at Layer2 (A, B, & C are on the same subnet and communicate by addressing each other's MAC), using Policy-based routing and Layer2 access lists, and NOT, 

"If A, B or C sends a telegram he can do this only with the mac address of me".

 

Alternatively, if you want, 
"If A, B or C sends a telegram he can do this only with the mac address of me"
to be true, then you need A, B, and C to all be in different subnets, with the switch performing the routing.

 

Essentially, 

"I want to be a "ethernet repeater" between all three connections."

contradicts

"If A, B or C sends a telegram he can do this only with the mac address of me"

 

You're either a layer2 device, with all devices in the same subnet, or you are Layer3, with all devices in 3 different subnets joined by a router.

 

The 1810 is a very basic switch which doesn't allow a whole lot of network management - just a bit of stuff you can change in the GUI. I'm pretty sure it's not going to support policy-based routing, let alone this "delay it, alter it" stuff..