Frame Forwarding over the Frame Relay Network
When the FR protocol receives a packet for encapsulation, it compares the packet’s
network address to the entries in the Address resolution Protocol (ARP) cache. If
the ARP cache contains the DLCI number that matches the network address, the
FR protocol encapsulates that packet into a frame and transmits the frame over its
specified local DLCI. If the ARP cache does not contain a match, the FR protocol
sends out an ARP request over all configured PVCs on the interface. When the
appropriate end-point responds with an ARP response, the FR protocol adds its
local DLCI that received the ARP response to theARP cache. Subsequent data
packets directed to the same network address are then encapsulated into a frame
and sent out over its local DLCI.
Protocol Addresses
Protocol addresses can be either mapped statically to FR network PVC addresses
or SVCs using locally configured names or discovered dynamically through Inverse
ARP or ARP.(For more information on ARP and Inverse ARP,see the
Protocol
Configuration and Monitoring Reference
.) Either method is protocol-dependent as
illustrated in Table 55.
Note: Static protocol addresses are also referred to as static ARP entries.A static
ARP entry is added to the configuration with the add protocol-address
command.
Table55. Protocol Address Mapping
Protocol Type ARP and Inverse
ARP Usage Static Mapping
VC Configured at
Protocol
Configuration
AP2 Yes Yes No
IP Yes Yes No
IPX Yes Yes No
Banyan VINES** No No No
DNAIV Yes Yes No
OSI*, ** No No Yes
* Youmust configure OSI at the protocol level to map the protocol address to the FR PVC.
** Not supported using SVCs.
Multicast Emulation and Protocol Broadcast
Multicast emulation is an optional feature that allows protocols requiring multicast
such as ARP to function properly over the FR interface. With multicast emulation, a
multicast frame is transmitted on each active PVC. By using the enable and
disable multicast commands, you can turn this feature on or off. Protocols that
utilize multicast are AP2,ARP, Banyan VINES, DNA4, IP, and IPX.
Protocol broadcast is another optional feature that allows the IP RIP protocol to
function properly over the FR interface. By using the enable protocol-broadcast
and disable protocol-broadcast commands, you can turn this feature on or off.
For protocols that support ARP/InARP over Frame Relay,Frame Relay will only
multicast a protocols packets over a circuit if a protocol address was either learned
or configured for that circuit.
Using Frame Relay
394 MRS V3.2 Software User’s Guide
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