Etherchannel between switch vs Stacked Switches - how is it done ?

[SJ K]

Hi all,

I might not understand the whole picture correctly, please pardon me if i have ask some illogical questions with regards to the topic above.

q1) If I have switch A and B daisy chain together via etherchannel (fa0/23,fa0/24),  can I have Server A with 2 NIC interfaces, with each interface connect to Switch A (fa0/1) and B (fa0/1) separately and create an ether channel on the 2 links ?

If the answer above is that you need to stack Switch A and B together, then why ?

q2) Assuming if the 2 switch are stacked, but connecting to the same router

Server A --- SWITCH A --- Router
              \          ||              /
               --- SWITCH B --

how do i make the 2 interface of the router to be long to the same network  and have only 1 interface IP as Server A's gateway ?
--> do i configure etherchannel on the router ports as well to be link with the switches ?
 

Regards,
Noob

[Jon Marshall]

q1) they need to be stacked or running VSS (or Nexus switches with vPC)

This is because two separate switches connected via an etherchannel trunk do not act as a single switch so they would not know that the connections from the server are part of the same etherchannel.

q2) the router would need to support etherchannel and in addition the stack would need to support L3 MEC which they may not do.  

I have never done this setup.

But it's not an issue because you can simply use two separate P2P links with different IP subnets and connect them to different switches in the stack.

Jon

[SJ K]

Hi Jon,

Thanks for your reply.

This is because two separate switches connected via an etherchannel trunk do not act as a single switch so they would not know that the connections from the server are part of the same etherchannel.

q1) Hence in such setup above, will LACP negotiation between the device and the switch succeed ? (just that to each individual switch, each etherchannel is 1 link) or it will fail entirely.

When I said in my original response it would have to be a L3 MEC on the switch it wouldn't have to be because as you point out you could run a L2 etherchannel from the router to both switches in the stack and then have an SVI on the router for the L3 interface.  

q2) Can you elaborate further esp on "have an SVI on the router" - I thought SVI are for switches ?

Can we have a L2 etherchannel from the device to the stacked switch and another etherchannel from the stacked switch to the router ?

How does the SVI play a role in the above setup ?
 

q3) on 2 ends of a an etherchannel, can we have a L2 etherchannel on 1 end, and a L3 etherchannel on the other ?  (e.g. from switch to router)  ?

Regards,
Noob

[SJ K]

Hi guys,

Still around ? :)

Regards,
Noob

[Jon Marshall · Accepted solution]

Just reread your question and realised the server's gateway is the router.

I was assuming the switches were L3 and the server's gateway was on there.

In that case ignore the last bit about using two P2Ps but the rest still stands.

Jon

[dasiimwe · Accepted solution]

I agree with Jon. Sorry for the repetition 

Q1: switches have to be stacked. why? With stackwise the switches actually run as one logical switch. Your 'daisy chain' etherchannel is just a trunk link between the two switches. They still run as two separate switches. .

Q2: agree with Jon. Tried to lab this on my 1841s and they don't support it on the integrated ports. You need a separate HWIC-4ESW.

[Jon Marshall · Accepted solution]

Daniel

No need to apologise, you raise a really good point that I overlooked. 

When I said in my original response it would have to be a L3 MEC on the switch it wouldn't have to be because as you point out you could run a L2 etherchannel from the router to both switches in the stack and then have an SVI on the router for the L3 interface.  

Jon