How to get 2 uplinks(active/standby)L2 switch via 2 different EVPL

[Herald Sison]

We have 1 main site with a core switch that holds dhcp/dns server and the internet source and a subsite with an L2 switch.

Both sites are connected via EVPL connection and that forwards only L2 traffic and does not recognize a trunk mode configuration.

Now we decided another 2nd EVPL from a different provider and we made some configs to make this 2 EVPL run as active/standby but we kept getting loop errors and pors were shut.

Any suggestion for this scenario. See image sample below.

[M02@rt37]

Hello @Herald Sison 

Does sub site’s L2 switch support STP ? So, set one of the uplinks ( ISP-B/EVPL 2 ?) to have higher path cost to prefer the other link -> ISP-A/EVPL 1. That way, one link becomes forwarding, and the other goes bloking, avoiding loops...

[Herald Sison]

Hi M02@rt37 Thank you so much for this info.

I am thinking also about this STP thing. May i ask a best configuration sample on both ends for Core and L2 switch?

our L2 switch is capable of MST, PVST and RPVST

sample config for L2 switch is Port 47 is EVPL 2 and Port 48 is EVPL 1 and it only forward 1 vlan since it cannot handle trunking.

[M02@rt37]

You're so welcome @Herald Sison 

Do you know if your EVPL providers allow STP BPDUs to pass ?

[Herald Sison]

Hi M02@rt37 , That is the main issue here since EVPL only passes L2 and that is not protocol transparent, considering that trunking was not permitted initially

[Joseph W. Doherty]

It appears you've created a L2 loop.  If everything is active, it won't work correctly.  So, you need to physically (manually) break the loop by shutting down a single interface or you need to logically break the loop by using software, such as STP (as mentioned by M02@rt37 ), MST, REP, etc.  (The advantage of using software, standby would work automatically.)

Another approach, if possible, would be to route between the sites.  Besides it too being automatic, you may be able to use both EVPLs concurrently.  (Often pretty easy if about equal bandwidths, but if not, proportional usage may be possible too.)

[Joseph W. Doherty]

Oh, just to add to the possibility of using L3, if you only have a L2 only switch at the remote site (NB: some Cisco L2 switches offer very limited L3).

Rather than replacing your L2 switch, you could "front" it with a very small, and inexpensive, L3 switch.

[Herald Sison]

can i ask a simple config for maybe RVST?
L2 Switch is running VLAN1 with 192.168.250.0 and from the core it is tagged as VLAN 250. would that matter in RVST?
L2 port 47 is EVPL2 and port 48 is EVPL1 and for Core port 3 is EVPL2 and port 4 is EVPL4

[Joseph W. Doherty]

"can i ask a simple config for maybe RVST?"

Simplest config is just setting it as the global setting.

An important additional configuration is setting portfast on edge ports (which can be configured, globally, as the default for access ports.)

Both PVST variants, are per VLAN, so you only have redundancy if you loop VLANs.  Also, when using VLANs, L2 loops can only happen per VLAN.