Cabletron Systems CSX1000 - Manual (Page 260)

USER’S GUIDE
260 CyberSWITCH
Bridge to Bridge Environment
As shown in the picture above, when a remote LAN is connected with bridge devices, the DHCP
server and clients communicate with each other as if they were on the same LAN. This is one
example configuration of how DHCP can be used to accomplish the dynamic IP address
assignment to the remote IP devices. (Note: This topology works without enabling any additional
DHCP/BOOTP features.)
Router to Bridge Environment
Although the bridge to bridge environment is a simple way to deploy the dynamic IP address
assignment using DHCP, it has some disadvantages. The major disadvantage is a broadcast storm.
Since all remote LANs are connected through bridge devices, all broadcast traffic will be forwarded
from one remote LAN to all the other LANs, and from a central LAN to all other remote LANs. This
is especially undesirable in the environment where there are many remote LANs.
To solve this problem, IP routing should be turned on at the central site. Enabling routing at the
central site will prevent the broadcast traffic from traveling all over the wide area network.
Unfortunately, this also keeps DHCP messages from being exchanged, as they are transmitted in
the broadcast packets. The DHCP Relay Agent resolves this situation, allowing only DHCP
messages to be forwarded without letting all other broadcast traffic get through.
CSX1200 Using bridging
Remote Bridge
DHCP Client DHCP Client
DHCP
DHCP Server
POWER SERVICE TX RX 10BASE - T LAN B-CHANNELS E1 ONLY
B2 B4 B6 B8 B26 B28 B22 B24 B18 B20 B14 B16 B10 B12 B30 L1
B1 B3 B5 B7 B25 B27 B21 B23 B17 B19 B13 B15 B9 B11 B29 B31 E1 D T1 D