Exam 300-420 topic 1 question 113 discussion

VPLS is a way to share the same subnet at multiple sites. Using NAT to hide the overlapping subnets does not make sense and defeats the purpose. A few are caught up in the idea that the PE side should be configured with 802.1Q, but they must be looking at the configuration guide for the PE only. You are perfectly fine with configuring 802.1Q on the CE side, and it is required to use multiple VLANs.

NAT is required for duplicate IPs - B

When connecting multiple sites that use the same IP subnet over a VPLS (Virtual Private LAN Service) network, it is essential to include route exchange with the service provider. VPLS is a Layer 2 VPN technology that extends the LAN segment across multiple sites, including the headquarters and remote locations. In such a scenario, the service provider plays a crucial role in ensuring that traffic is appropriately routed between the sites. Route exchange with the service provider allows the service provider's network to understand the reachability of each site's IP subnets. This enables proper routing of traffic within the VPLS network, despite the overlapping IP subnets at different locations.

Cisco config guide states 802.1q should be configured on the PE side, not CE.. I am going with B

Being in the same subnet does not mean there is an issue as long as there are no duplicate IPs

VPLS is a L2 WAN technology therefore it makes sense that the answer be C and not B. NAT has nothing to do with this. The same IP subnet is nothing more than extending a subnet/vlan across a WAN to other sites.

Because VPLS is a L2 VPN topology, the best answer here is C, you need to configure VLAN on the CE side of the LANs at each site. This is the best answer. NAT can also be used but it will be way more work as you would have to manage several IP networks and handle all of those translations, and they are planning on scaling.

B. address translation to hide overlapping subnets When connecting multiple sites with the same IP subnet using VPLS, the engineer must include address translation to hide overlapping subnets. VPLS (Virtual Private LAN Service) is a Layer 2 VPN technology that allows multiple sites to appear as if they are connected to the same LAN segment, but each site must use a unique IP subnet. Address translation is used to map the overlapping IP subnets to unique subnets, allowing them to be transmitted across the VPLS network without conflicts.

Therefore LAn users would be on a different subnet behind CE and would still ned to NAT to ISP subnet... B

I think the question meant all the CE routers on same subnet.

I'm going with C. The question states all sites use the same subnet... while answer "B" states [... NAT to hide overlapping subnetS ...]. To me this just doesn't sound correct because there is only 1 subnet in question and that answer uses the plural form of that word, also the question uses the words "must include" and you can absolutely get this working without any NAT involved if you treat it simply as a Layer2 extension (just don't have overlapping IPs). "C" sounds more correct here because yeah if you use a VPLS circuit to extend a broadcast domain obviously you need to tag that traffic with a VLAN before you can even send it into the VPLS circuit.

Question states "All the sites use the same IP subnet.", thus NAT is needed.

"VPLS is a type of VPN that allows for the connection of multiple sites into a single L2 domain over a managed IP/MPLS network". So the VPN represents a L2 "virtual switch".