Ethernet LAN

	Patton	Patton 1082/C
	Patton	connected to a router
	1082/I	connected to a router
	1082/I
	Bridge

PEC device with serial interface

Figure 2. Cisco router with serial interface, conﬁgured as PPP Half-Bridge

Figure 2 shows a typical Cisco router with a serial interface conﬁgured as a PPP Half Bridge. The router serial interface uses a remote device that supports PPP bridging to function as a node on the remote Ethernet network. The serial interface on the Cisco will have an IP address on the same Ethernet subnet as the bridge.

For example, the customer site is assigned the addresses 192.168.1.0/ 24 through 192.168.1.1/24. The address 192.168.1.1/24 is also the default gateway for the remote network. The above settings remove any routing/forwarding intelligence from the CPE. The associated Cisco con- ﬁguration will set serial interface (s0) to accommodate half bridging for the above example.

Authentication is optional under PPP. In a point-to-point leased-line link, incoming customer facilities are usually ﬁxed in nature, therefore authen- tication is generally not required. If the foreign device requires authenti- cation via PAP or CHAP, the PPP software will respond with default Peer- ID consisting of the units Ethernet MAC address and a password which consists of the unit’s Ethernet MAC address.

Some networking systems do not deﬁne network numbers in packets sent out over a network. If a packet does not have a speciﬁc destination network number, a router will assume that the packet is set up for the local segment and will not forward it to any other sub-network. However, in cases where two devices need to communicate over the wide-area, bridging can be used to transport non-routable protocols.