What is the purpose of Inverse ARP?
A.
to map a known IP address to a MAC address
B.
to map a known DLCI to a MAC address
C.
to map a known MAC address to an IP address
D.
to map a known DLCI to an IP address
E.
to map a known IP address to a SPID
F.
to map a known SPID to a MAC address
Explanation:
http://www.ciscopress.com/articles/article.asp?p=170741&seqNum=4
Frame-Relay (a Layer 2 protocol) uses Inverse-Arp to map a know Layer 2 Address (DLCI) to a
unknow Layer 3 Address. Dynamic Mapping Dynamic address mapping relies on the Frame Relay
Inverse Address Resolution Protocol (Inverse ARP), defined by RFC 1293, to resolve a next hop
network protocol address to a local DLCI value. The Frame Relay router sends out Inverse ARP
requests on its Frame Relay PVC to discover the protocol address of the remote device connected to
the Frame Relay network. The responses to the Inverse ARP requests are used to populate an
address-to-DLCI mapping table on the Frame Relay router or access server. The router builds and
maintains this address-toDLCImapping table, which contains all resolved Inverse ARP requests,
including both dynamic and static mapping entries. When data needs to be transmitted to a remote
destination address, the router performs a lookup on its routing table to determine whether a route
to that destination address exists and the next hop address or directly connected interface to use in
order to reach that destination. Subsequently, the router consults its address-to-DLCI mapping table
for the local DLCI that corresponds to the next hop address. Finally, the router places the frames
targeted to the remote destination on its identified outgoing local DLCI. On Cisco routers, dynamic
Inverse ARP is enabled by default for all network layer protocols enabled on the physical interface.Packets are not sent out for network layer protocols that are not enabled on the physical interface.
For example, no dynamic Inverse ARP resolution is performed for IPX if ipx routing is not enabled
globally and there is no active IPX address assigned to the interface. Because dynamic Inverse ARP is
enabled by default, no additional Cisco IOS command is required to enable it on an interface.
Example 4-16 shows the output of the show frame-relay map privileged EXEC mode command. The
addressto-DLCI mapping table displays useful information. The output of the command shows that
the next hop address 172.16.1.2 is dynamically mapped to the local DLCI 102, broadcast is enabled
on the interface, and the interface’s status is currently active.
NOTE After enabling Frame Relay on the interface, the Cisco router does not perform Inverse ARP
until IP routing is enabled on the router. By default, IP routing is enabled on a Cisco router. If IP
routing has been turned off, enable IP routing with the ip routing command in the global
configuration mode. After IP routing is enabled, the router performs Inverse ARP and begins
populating the address-to-DLCI mapping table with resolved entries.