Cisco 300-540 Dumps

In Cisco data center and cloud-scale designs, adouble-sided vPC(also called vPC-to-vPC) is used when both ends of a Layer 2 port channel are formed by a pair of switches that operate as vPC peers. In this model:

On the aggregation or leaf side, two switches (in this case,LEAF1 and LEAF2) form a vPC domain with a vPC peer-link and keepalive.

On the access or ToR side, two switches (in this case,TOR1 and TOR2) must also form their ownvPC domainwith a peer-link and vPC keepalive.

The port-channel that interconnects the two vPC domains is then configured as a vPC on both sides, creating a vPC-to-vPC topology.

The problem statement specifies thatLEAF1 and LEAF2 are already configured as vPC peers. For a double-sided vPC to work, the other side (TOR1 and TOR2) must also behave as a single logical entity for the downstream Cisco UCS server and for the upstream vPC connection towards LEAF1 and LEAF2. This is only achieved when TOR1 and TOR2 are configured as vPC peers with:

A vPC domain ID

A vPC peer-link between TOR1 and TOR2

vPC member port-channels towards LEAF1 and LEAF2 and towards the Cisco UCS server

Therefore, the next required step is to configure avPC between TOR1 and TOR2.

Evaluation of the options:

Option A, “Add all the switches to the fabric,” is generic and not specific to vPC configuration. It does not address the technical requirement to form a vPC domain on the ToR side.

Option B, “Configure peering between LEAF1 and LEAF2 and TOR1 and TOR2,” is incorrect because vPC peering is only configured between the two switches that form each vPC domain (LEAF1–LEAF2 and TOR1–TOR2), not across all four switches together.

Option C, “Configure MSTP between TOR1 and TOR2,” is not required for establishing a double-sided vPC. vPC designs rely on the vPC control plane and the peer-link, not on spanning-tree between the vPC peers for normal operation.

Option D, “Configure a vPC between TOR1 and TOR2,” correctly describes configuring TOR1 and TOR2 as a vPC pair (vPC domain with peer-link), which is the mandatory step to create a double-sided vPC topology with LEAF1 and LEAF2.

R1 (AS 200) is multihomed to:

SP-1 in AS 300 via neighbor172.16.1.1

SP-2 in AS 400 via neighbor172.16.2.1

R1 must:

Advertiseonly locally originated prefixes(its own network 10.10.0.0/24).

NOTbecome atransit AS—i.e., R1 mustnotadvertise routes learned from one provider to the other.

The configuration includes AS-path access-lists:

ip as-path access-list 1 permit ^$

ip as-path access-list 200 permit ^200

ip as-path access-list 300 permit ^300

ip as-path access-list 400 permit ^400

^$ in AS-path ACL1matcheslocally originated routes(empty AS-path).

ACLs 200, 300, and 400 match routes whose first AS in the path is 200, 300, or 400 respectively (used if we needed to match those provider or customer routes).

To ensure each upstream provider only receiveslocally originatedroutes, we apply AS-path ACL1as anoutbound filter-liston each external BGP neighbor:

router bgp 200

neighbor 172.16.1.1 remote-as 300

neighbor 172.16.1.1 filter-list 1 out ← only advertise local prefixes to SP-1

neighbor 172.16.2.1 remote-as 400

neighbor 172.16.2.1 filter-list 1 out ← only advertise local prefixes to SP-2

This way:

Routes learned from SP-1 (AS 300) willnotbe advertised to SP-2 (AS 400) because their AS-path will begin with 300, not empty, so they fail ACL 1.

Similarly, routes from SP-2 will not be sent to SP-1.

Only R1’s own prefixes are exported, preventing AS 200 from becoming a transit network.

In a VXLAN BGP EVPN fabric, each VTEP (NVE interface) must useBGP EVPN as the host-reachability protocolso that MAC/IP information and VTEP reachability are exchanged through the control plane.

From the exhibit:

LEAF-SW-1 – interface nve1

source-interface loopback0

No host-reachability protocol bgp

Host Learning Mode: Data-Plane in show nve interface

LEAF-SW-2 – interface nve1

source-interface loopback0

host-reachability protocol bgp configured

This mismatch causes one VTEP to rely ondata-plane flood-and-learn, while the other usesEVPN BGP control-plane learning, leading to inconsistent and “corrupted” MAC/IP and ARP/ND information between the leaf switches.

The fix is to configure LEAF-SW-1 to also use BGP for host reachability:

interface nve1

host-reachability protocol bgp

Options B and D are incorrect because anycast VTEP designs intentionally share the sameprimaryloopback IP while usingdifferent secondary IPsandunique BGP router IDs. Option A (removing suppress-arp) does not correct the control-plane mismatch.

Therefore, enabling host-reachability protocol bgp on LEAF-SW-1 (OptionC) resolves the issue.