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8-2
C
8: LAN
HAPTER
IP Fragmentation
® B
E
PLEX
RIDGING
XTENSIONS
Figure 8-1 illustrates the threshold mechanism for the multicast packet
firewall. For information on setting this threshold, see the LANplex® 2500
Administration Console User Guide.
Receive
rate
400 Packets/second
Threshold
Figure 8-1 Multicast Packet Firewall Threshold Mechanism
With IP fragmentation, FDDI and Ethernet stations connected to a LANplex
2500 system can communicate using IP even if the FDDI stations are
transmitting packets that are too large to bridge.
The maximum length of the information field in an FDDI packet is 4478
bytes, but the maximum length of the information field in an Ethernet
packet is only 1500 bytes. Therefore, any packet sourced from an FDDI
station and destined for an Ethernet station must have an information field
that does not exceed 1500 bytes to bridge the packet in a conventional
fashion.
To overcome this limitation, the Internet Protocol (IP) specifies a procedure,
called IP fragmentation. This allows a large FDDI packet to be "fragmented"
into smaller packets.
Multicast/broadcast frames received
Multicast/Broadcast Frames Forwarded
Multicast/
broadcast
storm
Firewall
Time
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