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Port-Channel between Two Switches and a Server can Generate a loop?

We have two switches 4500 connected together via 802.1 trunk. We have a server with 4 NICs capable of LACP. 

 

We connected 2 NICs to one Switch and the other 2 NICs to the other Switch. The interfaces of the switch are in access mode in a VLAN. The 4 NICs are configure with an IP address corresponding to that vlan segment. 

 

Can this generate a layer 2 loop in the network?

1 ACCEPTED SOLUTION

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VIP Mentor

Hello


@Carlosperez1601 wrote:

We have two switches 4500 connected together via 802.1 trunk.

 

We connected 2 NICs to one Switch and the other 2 NICs to the other Switch. The interfaces of the switch are in access mode in a VLAN. The 4 NICs are configure with an IP address corresponding to that vlan segment. 

There is only one Ip address configure on the server. The 4 Nics are logically merged and running LACP. 


This suggests the server nics are teamed together -  Can you confirm please? - 

 


@Carlosperez1601 wrote:

Can this generate a layer 2 loop in the network? - <depends


Do each teamed nic pair have a ip address in a different vlan if so then no a loop shouldn't be formed, However you would require the switch ports also to form a port-channel for each teamed pair, do you have this?

 



kind regards
Paul

Please rate and mark posts accordingly if you have found any of the information provided useful.
It will hopefully assist others with similar issues in the future

View solution in original post

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VIP Mentor

what is the goal for availability ? how is these switches connected ? they have Layer 2 connection ?

 

The 4 NICs are configure with an IP address corresponding to that vlan segment.  - I believe and my understand , they are  4 different IP address configured is this correct ?

 

BB
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The switches are connected between with a trunk link.

There is only one Ip address configure on the server. The 4 Nics are logically merged and running LACP. 

 

 

Highlighted

If both the switches are trunk.

 

The best approach is MEC all 4 into one Switch ( 2 in the different blade, 2 in another blade  -in case blade fails)

 

What Server or Operating system is this? make sure you configure correctly or post us the screenshot along with switch configuration to look.

 

when do you see high traffic what traffic is this? legitimate or unnecessary?

You can use netflow / Span the port or Wireshark on the Server to see what traffic.

 

 

BB
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VIP Expert

Hello,

 

I don't think this is going to work. For MEC (Multichassis EtherChannel) to work, your 4500 switches need to be combined in a VSS (Virtual Switching System).

Highlighted

We shutdown one of the port-channel between the server and one of the switches and we continue to experience high traffic and slowness in the network. Apparently that was not the root cause of the problem.

 

We are experiencing high traffic problems on the trunk interfaces directly connected to our Switches-Core and we believe it is caused by loops or broadcast problems. 

 

- We checked on all switches that there are no loops.

We verify that only the interfaces directly connected to the Switches-Core have a high receive traffic, and this traffic is not transmitted to any other Switch or host.

 

How could I detect what is generating this traffic?

Highlighted
VIP Mentor

Hello


@Carlosperez1601 wrote:

We have two switches 4500 connected together via 802.1 trunk.

 

We connected 2 NICs to one Switch and the other 2 NICs to the other Switch. The interfaces of the switch are in access mode in a VLAN. The 4 NICs are configure with an IP address corresponding to that vlan segment. 

There is only one Ip address configure on the server. The 4 Nics are logically merged and running LACP. 


This suggests the server nics are teamed together -  Can you confirm please? - 

 


@Carlosperez1601 wrote:

Can this generate a layer 2 loop in the network? - <depends


Do each teamed nic pair have a ip address in a different vlan if so then no a loop shouldn't be formed, However you would require the switch ports also to form a port-channel for each teamed pair, do you have this?

 



kind regards
Paul

Please rate and mark posts accordingly if you have found any of the information provided useful.
It will hopefully assist others with similar issues in the future

View solution in original post

Highlighted

This suggests the server nics are teamed together -  Can you confirm please? 

 

          Yes. The server NICs were teamed together, so we had a loop formed. 

 

Thanks for your help.

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