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Figure 1.
Cisco router with serial interface, configured as PPP Half Bridge.
Figure 1 shows a typical Cisco router with a serial interface configured
as a PPP Half Bridge. The router serial interface connects to the WAN
via a 2707/C (V.35) E1 NTU and to the remote 2707/I with support for
PPP bridging. The 2707/I functions 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 2707/I. The associated Cisco
configuration 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.
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.
Customer’s Site
Model 2707/I
E1
Service Provider’s Network
Internet
Model 2707/C
Router
Ethernet
LAN
!
interface s0
ppp bridge ip
ip address 192.168.1.1 255.255.255.0
!