03-22-2013 04:01 AM - edited 03-07-2019 12:25 PM
Hello,
I've been searching quite extensively on Google, but haven't found anything that I've got working.
For testing purposes I want traffic transmitted into the switch to pass through all the physical ports. To achieve this I will patch the ports in pairs and then make a logical connection between each pair. Is this possible? So far the traffic has just skipped all the jumpered ports. Also, I'm quite new to this in case that wasn't obvious
Thanks in advance.
/Marc
Solved! Go to Solution.
03-22-2013 05:28 PM
So what you're trying to do is called a snake test.
This is where traffic will ingress port 1, be switched across the switch backplane to egress port 2, which being externally connected via some form of cross-over cable to port 3, will see the traffic ingress on port 3, through the backplane to port 4, and so on for as many ports as you wish to test.
The ASCII art setup for an imaginary 8-port switch would be as follows:
|-<- gi1/1 (Vlan2) -<- traffic generator tx
|
|->- gi1/2 (Vlan2) ->-|
| x-over cable
|-<- gi1/3 (Vlan3) -<-|
|
|->- gi1/4 (Vlan3) ->-|
| x-over cable
|-<- gi1/5 (Vlan4) -<-|
|
|->- gi1/6 (Vlan4) ->-|
| x-over cable
|-<- gi1/7 (Vlan5) -<-|
|
|->- gi1/8 (Vlan5) ->- traffic generator tx
The key to the configuration is a deliberate mismatch of VLANs on the ports connected via the cross-over cables. So for the above we would have a configuration as follows:
!
interface gi1/1
switchport mode access
switchport access vlan 2
!
interface gi1/2
switchport mode access
switchport access vlan 2
!
interface gi1/3
switchport mode access
switchport access vlan 3
!
interface gi1/4
switchport mode access
switchport access vlan 3
!
interface gi1/5
switchport mode access
switchport access vlan 4
!
interface gi1/6
switchport mode access
switchport access vlan 4
!
interface gi1/7
switchport mode access
switchport access vlan 5
!
interface gi1/8
switchport mode access
switchport access vlan 5
!
There's no routing here, so although we have switchports configured in different VLANs, as far as the traffic generator is concerned the IP address of both the transmit and receive interfaces are in the same subnet.
I suspect where you're going wrong at the moment is that you have the traffic generator Tx and Rx ports in the same VLAN. This would mean that traffic ingress gi1/1 is sent directly via the switch backplane to gi1/8. The important point is that the traffic generator Tx and Rx ports must be in different VLANs such that the only path between them is via the ports you wish to test.
Regards
Message was edited by: Steve Fuller Added HTML tags to format ASCII art correctly
03-22-2013 09:09 PM
Hello Steve,
Looks nice I would also suggest deactivating CDP to stop complaining about native VLAN mismatch, and assuming there is no physical loop, also deactivating the STP as it also may not like being tricked into this kind of topology, i.e.:
no cdp run
no spanning-tree vlan 1-4094
Best regards,
Peter
03-22-2013 06:05 AM
I don't think that is possible. What are you ultimately trying to accomplish?
03-22-2013 06:13 AM
I'm checking ports for errors. Transmitting a large file through the switch then CRC-checking it, two ports at a time, is time-consuming. I wanted to check all the ports at once by jumpering them all, with the exception of two ports at each end for traffic I/O.
Thanks for answering though!
Best regards, Marc
03-22-2013 06:21 AM
Why check every port? Are you thinking that you may have some bad ones? Typically CRC/input errors are cause by one side negotiating full duplex and the other side half.
03-22-2013 11:22 AM
I've been tasked with testing switches at the moment. I have no reason to believe they are defect, but I have to check them thoroughly.
03-22-2013 05:28 PM
So what you're trying to do is called a snake test.
This is where traffic will ingress port 1, be switched across the switch backplane to egress port 2, which being externally connected via some form of cross-over cable to port 3, will see the traffic ingress on port 3, through the backplane to port 4, and so on for as many ports as you wish to test.
The ASCII art setup for an imaginary 8-port switch would be as follows:
|-<- gi1/1 (Vlan2) -<- traffic generator tx
|
|->- gi1/2 (Vlan2) ->-|
| x-over cable
|-<- gi1/3 (Vlan3) -<-|
|
|->- gi1/4 (Vlan3) ->-|
| x-over cable
|-<- gi1/5 (Vlan4) -<-|
|
|->- gi1/6 (Vlan4) ->-|
| x-over cable
|-<- gi1/7 (Vlan5) -<-|
|
|->- gi1/8 (Vlan5) ->- traffic generator tx
The key to the configuration is a deliberate mismatch of VLANs on the ports connected via the cross-over cables. So for the above we would have a configuration as follows:
!
interface gi1/1
switchport mode access
switchport access vlan 2
!
interface gi1/2
switchport mode access
switchport access vlan 2
!
interface gi1/3
switchport mode access
switchport access vlan 3
!
interface gi1/4
switchport mode access
switchport access vlan 3
!
interface gi1/5
switchport mode access
switchport access vlan 4
!
interface gi1/6
switchport mode access
switchport access vlan 4
!
interface gi1/7
switchport mode access
switchport access vlan 5
!
interface gi1/8
switchport mode access
switchport access vlan 5
!
There's no routing here, so although we have switchports configured in different VLANs, as far as the traffic generator is concerned the IP address of both the transmit and receive interfaces are in the same subnet.
I suspect where you're going wrong at the moment is that you have the traffic generator Tx and Rx ports in the same VLAN. This would mean that traffic ingress gi1/1 is sent directly via the switch backplane to gi1/8. The important point is that the traffic generator Tx and Rx ports must be in different VLANs such that the only path between them is via the ports you wish to test.
Regards
Message was edited by: Steve Fuller Added HTML tags to format ASCII art correctly
03-22-2013 09:09 PM
Hello Steve,
Looks nice I would also suggest deactivating CDP to stop complaining about native VLAN mismatch, and assuming there is no physical loop, also deactivating the STP as it also may not like being tricked into this kind of topology, i.e.:
no cdp run
no spanning-tree vlan 1-4094
Best regards,
Peter
03-23-2013 01:01 AM
I see now what I did wrong, I assumed one _had_ to set ip addresses for the VLANs and since it's not possible to put two different VLANs in the same subnet when assigning them IP addresses, they wouldn't communicate. So I thought maybe there was a way to achieve this by trunking and creating etherchannels, but I never got that to work either.
Well, anyhow, that is exactly what I was looking for! Hats off to you my good sir!
Best regards, Marc
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