CCNA Cisco Certified Network Associate Study Guide - FTP Server

Frame Relay 491
7. The CO receives the frame and sends it through the Frame Relay
“cloud” to its destination. This cloud can be dozens of switching
offices—or more! It looks for the destination IP address and DLCI
number. It typically can find the DLCI number of the remote device or
router by looking up an IP-to-DLCI mapping. Frame Relay mappings
are usually created statically by the service provider, but they can be
created dynamically using the Inverse ARP (IARP) protocol. Remember
that before data is sent through the cloud, the virtual circuit is created
from end to end.
8. Once the frame reaches the switching office closest to the destination
office, it is sent through the local loop. The frame is received at the
demarc and then is sent to the CSU/DSU. Finally, the router extracts
the packet, or datagram, from the frame and puts the packet in a
new LAN frame to be delivered to the destination host. The frame on
the LAN will have the final destination hardware address in the
header. This was found in the router’s ARP cache, or an ARP broadcast
was performed. Whew!
The user and server do not need to know, nor should they know, everything
that happens as the frame makes its way across the Frame Relay network.
The remote server should be as easy to use as a locally connected
resource.
Frame Relay Encapsulation
When configuring Frame Relay on Cisco routers, you need to specify it as an
encapsulation on serial interfaces. There are only two encapsulation types:
Cisco and IETF (Internet Engineering Task Force). The following router
output shows the two different encapsulation methods when choosing
Frame Relay on your Cisco router:
RouterA(config)#int s0
RouterA(config-if)#encapsulation frame-relay ?
ietf Use RFC1490 encapsulation
The default encapsulation is Cisco unless you manually type in IETF, and
Cisco is the type used when connecting two Cisco devices. You’d opt for
the IETF-type encapsulation if you needed to connect a Cisco device to a