Posted on November 5, 2019 6:30 pm
 |  Asked by Félix Bouynot
 |  64 views
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Hello,

I’m trying to setup the following topology (Backbone is Arista 7280SR, Cust is Cisco N3K):

Bacbone A =========== Backbone B
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Cust site A ========= Cust site B

Cust is using some vlan, let’s say 100 to 200.
We share some vlans for internal usages, let’s say 2 and 3.
I’m q-in-qing all others vlan in let’s say vlan 10.

So, here are conf for Backbone A and B to respectively Cust A and B:

switchport trunk allowed vlan 2,3,10
switchport mode trunk
switchport vlan mapping 100-200 dot1q-tunnel 10
spanning-tree link-type point-to-point
spanning-tree guard loop

Backbone A to backbone B (and B to A):

switchport trunk allowed vlan 2,3,10
switchport mode trunk
spanning-tree link-type point-to-point
spanning-tree guard loop

And the conf for Cust site A and B to every other:

switchport mode trunk
switchport trunk allowed vlan 2,3,100-200
spanning-tree link-type point-to-point
spanning-tree guard loop

This topology create a L2 loop which is not mitigated by spannin-tree.
Vlan 2-3 doesn’t create loop.
Vlan 100-200 / 10 are.

If EOS were NX-OS, I could just do on Arista to Cisco interfaces:
l2protocol-tunnel stp
Well, i would need to be able to do that on only vlan 100-200 encapsulation in 10 anyway.

Is there a way for me to keep this redundancy but avoid the l2 loop?

Thank you

1
Answered on November 5, 2019 8:55 pm

Hi Felix,

Thank you for writing to the forum. May I know what is the EOS version on the 7280SR?

We do support L2 forwarding on the platform. More details are here:

https://eos.arista.com/eos-4-22-0f/l2-protocol-forwarding/
https://eos.arista.com/eos-4-21-0f/l2-protocol-forwarding/

Thank you,

Hello, Thank you very much for pointing me this! [Note: because of bad formatting, we don't see but Backone B and Cust site B are linked too] The version is 4.21.3F, so it looks like I need to upgrade to 4.22.0F to be able to support Ethernet ports and tag / untag keywords with L2 forwarding. Then, I need to create a specific hardware tcam profile with what's in your first link and apply it. Then, I need to configure a l2-protocol forwarding profile, and apply it to the interface. The documentation example is: switch(config-l2-protocol)# forwarding profile abc switch(config-l2-protocol-abc)# lacp forward switch(config-l2-protocol-abc)# stp untagged forward switch(config-l2-protocol-abc)# exit switch(config-l2-protocol)# With rapid-pvst, PVST+ BPDU are sent tagged except for vlan 1. In my example, how am I supposed to differentiate vlan 2 & 3 BPDU from vlan 100-200 BPDU? Wouldn't "stp untagged forward" create a loop for vlan 2 & 3 ? Thank you,
(Félix Bouynot at November 6, 2019 11:26 am)

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