UDP Port and Static IP Address Conflict

[DylanHawkes67427]

Hello,

I have Cisco Catalyst 3560 network switch and am trying to receive UDP packets from four attached devices. Each device is sending packets to the same ip address and port, and this destination address cannot be changed. Is it possible to redirect which ip address or port the devices reach using the switch so that the traffic can be distinguished? Ideally I would say all traffic on ethernet port 1 goes to a certain ip address and port, and all traffic ethernet port 2 goes to another, etc.

Thanks,

[Deepak Kumar]

Hi,

Do you have multiple devices with a single Destination IP address? 

[DylanHawkes67427]

Yes that’s correct. They all have the same destination IP and port, and
this can’t be changed.

[Captain HoOmi]

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@DylanHawkes67427 wrote:

this Ideally I would say all traffic on ethernet port 1 goes to a certain ip address and port, and all traffic ethernet port 2 goes to another, etc.

Thanks,

---

You can use PBR, it is supported on 3560:

https://www.cisco.com/c/en/us/td/docs/switches/lan/catalyst3750e_3560e/software/release/12-2_46_se/configuration/guide/scg/swintro.html#wp1528015

"•Policy-based routing (PBR) for configuring defined policies for traffic flows"

Something like this:

ip access-list extended PBR
permit ip X X  any ( Source IP you want to redirect)

!

route-map PBR permit 10
match ip address PBR
set ip default next-hop 192.168.1.1 ( the IP you want to redirect traffic to)

Please rate the post if find it useful.

[Deepak Kumar]

Hi,

The issue is the Destination IP address and directly connected on the Switches, so He will get an IP conflict error message.

Is it possible to change the Traffic Destination IP address on the traffic sender? If yes, then put the device behind the NAT and your issue will resolve without any PBR also.

[pieterh]

I met a similar problem with cheap HDMI extenders 

The manufacturer obviously has not enough  knowledge on the subject of networking.

all devices are flashed with the same software image including IP-address and MAC address

as a result they all use the same ip-address and even the same MAC-address

Here the problem was "solved" by creating a separate VLAN for each set of HDMI-transmitter/reciever(s).

with the cost of administering additional vlans

source1 and destination1 are ports in the same vlan etc, this resolves you requirement

all traffic on ethernet port 1 goes to a certain ip address and port, and all traffic ethernet port 2 goes to another, etc.

if you need all devices to communicate with the same destination you need a different solution

L2NAT may be something to investigate.

[DylanHawkes67427]

Unfortunately I cannot change the destination IP address, and I do need them all to communicate with the same device. PBR won't work (if I understand correctly) because it would just route all of the traffic to a different IP address, yielding the same issue. I tried using VLANs, but that doesn't fix the issue since there will still be conflicts on the host machine.

If I purchased something with NAT support, would it be possible to setup a NAT on a per interface basis that would translate the destination IP addresses to different IPs (ideally still inside the network, but outside might work as well)? Something else to note is that the source IP addresses are unique for the data that I am trying to receive. I was able to make a python script on the machine that filtered out information based on source IP and then sent it over different ports, but it was, predictably, far too slow.

I will checkout L2NAT and see if there's anything useful there.

Thanks for the suggestions.

[Captain HoOmi]

How about SPAN?  So you can have duplicate all the traffics on that port and send it to your destination port.