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Specify arp entry to a certain vlan

Hello

 

I have a maybe unusual case.

I have a catalyst 3750g switch with 3 vlans on it. Vlan 1 (native), Vlan 10 and Vlan 20.

On Vlan 10 i have a AIRSAP 702.

My goal is to monitor syslogs and some snmp data from both devices.

i use PRTG for that.

On the switch i only want to monitor the vlan 10 traffic via snmp because that is where all the ction im interessted takes place.

Therefore on the 3750 the VLAN 1 has the address 10.200.0.22 and the AP has 10.200.1.131.

This woks all fine as long as all devices re in the same vlan.

Note that i only have one laptop, meaning just one NIC.

 

So here is what is did:

My computer has 1 NIC with 2 addresses assigned; 10.200.0.101 to access the data of the 3750 and 10.200.1.11 to access the AP.  the laptop is connected to VLAN 1 obviously.

 

I don't want any routing to take place and i don't want to see any other traffic of that vlan 10 so i did maybe something unusual;

I connected the VLAN 1 and the VLAN 10 with a cable and permitted only the syslog data and the snmp data with an acc-list to receive just these protocols.

This works fine.

 

Now my problem is, that when i do he show arp command; the ip address that should olny reach VLAN 1 of the switch (10.200.0.101) is listed in vlan 10 and in order to that can't reach the addressed VLAN 1.

It all works fine for a few seconds when i clear the arp cache but after that the arp entry refers to vlan 10..

 

Is there a way to get around that issue with some acc list or anything?

To force that the mac/ip combination is only valid in vlan 1?

 

Thank you guys.

 

2 Replies 2

Hello,

 

I am not sure I fully understand your question and your setup: you have a 3750G, with an AIRSAP connected to the switch, and you want to use PRTG to only monitor traffic from VLAN 10?

 

Why don't you create a VLAN 10 interface with an IP address and then connect the laptop to a switchport in Vlan 10 ?

Hi George.

 

For practial circumstances this is what i will do i guess..

But just to learn a few more things i would be happy to know if my question is possible at all?

 

In my eyes there has to be a possibility to force a arp entry to attach to a certain vlan, isn't there?

 

Thank you

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