MBONE: Multicasting Tomorrow's Internet
Previous versions of the IP multicast software (before March 1993) used a different method of encapsulation based on an IP Loose Source and Record Route option. This method remains an option in the new software for backward compatibility with nodes that have not been upgraded. In this mode, the multicast router modifies the packet by appending an IP LSRR option to the packet's IP header. The multicast destination address is moved into the source route, and the unicast address of the router at the far end of the tunnel is placed in the IP Destination Address field. The presence of IP options, including LSRR, may cause modern router hardware to divert the tunnel packets through a slower software processing path, causing poor performance. Therefore, use of the new software and the IP encapsulation method is strongly encouraged.
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