LISP Practice Questions

Answers and explanations appear when you work through the set above.

1. In Locator/ID Separation Protocol (LISP), what is the function of an Egress Tunnel Router (ETR)?

   • It decapsulates LISP packets arriving from the core and forwards the inner packet to the local EID.
   • It encapsulates packets from local hosts and routes them across the core toward the remote site's RLOC.
   • It resolves EID-to-RLOC queries for remote sites by forwarding them into the ALT or DDT mapping system.
   • It assigns dynamic IP addresses to end systems from the EID prefix registered for the local site.

2. In Locator/ID Separation Protocol (LISP), what is the function of a Proxy Egress Tunnel Router (PETR)?

   • Lets non-LISP sites send traffic to LISP destinations by attracting it to the EID prefixes.
   • Lets LISP sites send traffic to non-LISP destinations across the core.
   • Registers the local site's EID prefixes directly with the Map-Server on behalf of ETRs.
   • Translates IPv4 LISP payloads into native IPv6 frames before handing them to the core.

3. In the Locator/ID Separation Protocol (LISP) framework, what address entity represents the permanent network layer identity assigned to an endpoint device?

   • Routing Locator (RLOC)
   • Endpoint Identifier (EID)
   • Virtual Network Identifier (VNI)
   • Transport Location (TLOC)

4. In a LISP-enabled network, which control-plane role receives a Map-Request from an Ingress Tunnel Router and forwards it toward the authoritative ETR or mapping system?

   • Map-Resolver (MR) / Map-Server (MS)
   • Egress Tunnel Router (ETR) default gateway
   • Proxy Egress Tunnel Router (PETR)
   • Core BGP Autonomous System Router

5. In Locator/ID Separation Protocol (LISP) architecture, what is the core operational distinction between an Endpoint Identifier (EID) and a Routing Locator (RLOC)?

   • EID is the host's address inside the site; RLOC is the routable address of the site's LISP router in the core.
   • EID is assigned to the LISP routers themselves, while the RLOC is the MAC address of each client in the site.
   • EID operates at Layer 2 for host mobility, while the RLOC operates at Layer 7 for application identity.
   • EID is encrypted with MACsec on the access link, while the RLOC is always sent as plaintext in the core.

6. Which LISP message does an ETR send to a Map-Server to advertise the EID prefixes it is authoritative for?

   • Map-Register
   • Map-Request
   • Map-Reply
   • Map-Notify-Ack

7. Which protocol does Cisco SD-Access use as its fabric control plane to track which fabric edge node each endpoint is currently attached to?

   • LISP (control plane nodes act as MS/MR)
   • OSPFv3 with segment routing (SR-MPLS) extensions
   • EIGRP stub routing with host-route summarization
   • RIPv2 with triggered updates per host

8. What operational advantage does LISP's separation of EID and RLOC provide when an endpoint physically moves to a different location in the fabric?

   • The endpoint must be assigned a new IP address from the new edge node's subnet after every move.
   • The endpoint keeps its EID; only its EID-to-RLOC mapping is updated, so nothing has to renumber.
   • Every move triggers a network-wide OSPF SPF recalculation so the core learns the new host route.
   • The move triggers a fabric-wide VLAN renumbering so the endpoint's VLAN matches its new port.

9. What is the role of the LISP Map-Cache maintained on an Ingress Tunnel Router (ITR)?

   • It stores the router's OSPF link-state database so it can compute underlay paths toward each RLOC.
   • It caches resolved EID-to-RLOC mappings so later packets are encapsulated without another Map-Request.
   • It holds the EID prefixes the local ETR registered, which the Map-Server polls when it gets a Map-Request.
   • It keeps a backup of the startup configuration so LISP settings survive a reload of the router.

10. Which LISP component is queried first by an ITR's Map-Request before that request is forwarded toward the authoritative ETR?

    • The Map-Resolver (MR)
    • A neighboring ITR
    • The destination host directly
    • The local VTP server

11. What encapsulation does LISP use to carry a packet from an ITR to an ETR across the underlying transport network?

    • A LISP header over UDP (port 4341) inside an outer IP header addressed to the destination RLOC.
    • Raw GRE (IP protocol 47) with no UDP header, addressed to the Map-Server that registered the EID.
    • 802.1Q VLAN tags only, with the VLAN ID mapped to the destination EID prefix at each hop.
    • An MPLS label stack, with one label per hop learned from LDP toward the destination RLOC.

12. In an SD-Access fabric using LISP as the control plane, what is the role of the fabric control plane node when a fabric edge node needs to forward traffic to an endpoint attached elsewhere in the fabric?

    • The edge node asks it which edge node (RLOC) the destination EID sits behind, then VXLAN-encapsulates the traffic.
    • The control plane node physically switches every packet in the fabric, so all traffic passes through it.
    • The edge node floods an ARP request to every other edge node, and the control plane node just logs replies.
    • The control plane node assigns VLAN IDs to each edge port, and the edge node forwards with plain 802.1Q.

13. In a LISP Map-Reply, what does it mean when the Authoritative (A) bit is set to 1?

    • The reply was proxied by a Map-Server, which caches every registered mapping for its sites.
    • The reply came from an ETR at the site that owns the EID prefix, not from a proxying Map-Server.
    • The reply was sent over a TLS-encrypted session, so the ITR can skip mapping validation checks.
    • The mapping has the highest TTL in the database and must be broadcast to every ITR in the domain.

14. What common use case motivates deploying LISP in a traditional (non-SD-Access) branch or campus network outside of fabric overlays?

    • IP mobility: moving subnets or VMs between sites or data centers without renumbering hosts.
    • Replacing NTP for clock synchronization between branch routers that share a common RLOC space.
    • Providing DHCP relay services to remote VLANs so hosts keep the same lease after every move.
    • Encrypting Layer 2 broadcast domains between sites with MACsec keys carried in Map-Registers.

15. In Locator/ID Separation Protocol (LISP), what does an RLOC represent?

    • The IP address assigned to an endpoint device in the local subnet behind the LISP site router.
    • The BGP autonomous system number of the egress border router that connects the site to the core.
    • The address of the LISP router's core-facing interface, which locates the site of an EID.
    • The virtual switch port identifier assigned to a VM inside a hypervisor host at the LISP site.