3com 812 Manual De Usuario

C

HAPTER

 6: M

ANUAL

 S

ETUP

Because routers base their forwarding decision on network-level addresses, 
packets that are routed over a WAN are transmitted without MAC-layer addresses. 
Additionally, address resolution procedures that can be used to determine the 
destination MAC address for a packet are not required. 

Conversely, packets that are bridged over a Wide Area Connection include 
MAC-layer information. Address resolution procedures are required. 

MAC-Encapsulated Routing uses network-level addresses for forwarding decisions 
but transmits MAC-layer addresses over the Wide Area Connection. Additionally, 
address resolution procedures are used. To the remote site, the packets appear as 
if they had been bridged. 

This feature allows the routing features of the OCR 812 (i.e., address translation, 
DHCP Server, DNS Proxy, etc.) to be employed in a bridged environment.

MAC-Encapsulated Routing is specified on a per-VC basis. When 
MAC-Encapsulated Routing is enabled in a VC profile, packets for the routed 
protocols configured by the profile (i.e., IP and/or IPX) will be sent using the 
appropriate bridged encapsulation. If the configured network service is RFC 1483, 
then the packets will be encapsulated in a bridged-1483 format. If the configured 
service is PPP, the packets will be encapsulated in BRCP.

To enable MAC-Encapsulated Routing in a VC profile, use the command:

set vc <vc_name> mac_routing enable

To disable the MAC-Encapsulated Routing in a VC profile, use the command:

set vc <vc_name> mac_routing disable

The OCR 812 can be configured for simultaneous bridging and routing. IP routing 
is configured if IP forwarding is enabled (see Enabling IP Routing). IPX routing is 
enabled if an IPX network is present over the Ethernet interface (see Configuring 
IPX for the LAN). Bridging is enabled by adding a bridge network over the Ethernet 
interface. (see Configuring Bridging for the LAN). Routing and bridging are 
enabled for each destination in its remote site profile. 

When configured for simultaneous bridging and routing, packets received from 
the LAN are first passed through the router for any configured protocols. If the 
packet can not be routed it is passed to the bridge depending on the setting of the 
Bridge Firewall function. 

The Bridge Firewall has three modes: 

1 Discard Routed Protocols:

This is the default mode. If a protocol is configured for routing and a packet for 
that protocol type is received from the LAN that is not addressed to the MAC 
address of the OCR 812, it is discarded. Additionally, broadcasts (including ARPs) 
for the protocol are not passed to the bridge. To configure the Bridge Firewall for 
this mode, use the command: