Which statement about LISP encapsulation in an EIGRP OTP implementation is true?
- A. LISP learns the next hop
- B. OTP uses LISP encapsulation to obtain routes from neighbors
- C. OTP uses LISP encapsulation for dynamic multipoint tunneling
- D. OTP maintains the LISP control plane
Explanation: The EIGRP Over the Top solution can be used to ensure connectivity between disparate EIGRP sites.
This feature uses EIGRP on the control plane and Locator ID Separation Protocol (LISP) encapsulation on the data plane to route traffic across the underlying WAN architecture. EIGRP is used to distribute routes between customer edge (CE) devices within the network, and the traffic forwarded across the WAN architecture is LISP encapsulated.
EIGRP OTP only uses LISP for the data plane, EIGRP is still used for the control plane. Therefore we cannot say OTP uses LISP encapsulation for dynamic multipoint tunneling as this requires encapsulating both data and control plane traffic -> Answer ‘OTP uses LISP encapsulation for dynamic multipoint tunneling’ is not correct.
In OTP, EIGRP serves as the replacement for LISP control plane protocols (therefore EIGRP will learn the next hop, not LISP -> Answer ‘LISP learns the next hop’ is not correct). Instead of doing dynamic EID-to-RLOC mappings in native LISP-mapping services, EIGRP routers running OTP over a service provider cloud create targeted sessions, use the IP addresses provided by the service provider as RLOCs, and exchange routes as EIDs. Let’s take an example:
If R1 and R2 ran OTP to each other, R1 would learn about the network 10.0.2.0/24 from R2 through EIGRP, treat the prefix 10.0.2.0/24 as an EID prefix, and take the advertising next hop 198.51.100.62 as the RLOC for this EID prefix. Similarly, R2 would learn from R1 about the network 10.0.1.0/24 through EIGRP, treat the prefix 10.0.1.0/24 as an EID prefix, and take the advertising next hop 192.0.2.31 as the RLOC for this EID prefix. On both routers, this information would be used to populate the LISP mapping tables. Whenever a packet from 10.0.1.0/24 to 10.0.2.0/24 would arrive at R1, it would use its LISP mapping tables just like in ordinary LISP to discover that the packet has to be LISP encapsulated and tunneled toward 198.51.100.62, and vice versa. The LISP data plane is reused in OTP and does not change; however, the native LISP mapping and resolving mechanisms are replaced by EIGRP.
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