Visara CNA-8000 Planning Guide - Manual (Page 21)

CNA-8000 Migration and Planning Guide
707156-002 2-7
Bit-Swapping LAN Addresses
Whenever you have a cross media LAN circuit connection between Ethernet and Token
Ring, you will probably need to bit-swap the LAN addresses to complete your
configuration. This is because of the way the address is identified between the two media.
The low order bit designation is opposite between the two LAN media. That is, the most
significant bit in one media is the least significant bit in the other media. This only
becomes an issue when you are entering the LAN addresses that you need as part of the
configuration.
The address that you enter for your media is always correct for your media, but if you are
referencing the address of another platform that is attached to the other media, then you
must reference the bit swapped version of that address. (For example the FEP-4600 is
attached to a Token Ring and the DSPU is attached through an LLC bridge on Ethernet.)
Following you will find an example of a procedure you can use to bit swap an address.
For the example, we will bit-swap the Token Ring address 40:00:37:45:00:16 to the
equivalent that would be seen on an Ethernet drop.
Bit swapping is performed on a byte by byte basis. Separating the address into individual
bytes, we end up with:
40
00 37 45 00 16
which translates to the binary representation of:
01000000 00000000 00110111 01000101 00000000 00010110
Now if we swap the bits of each byte we will have:
00000010 00000000 11101100 10100010 00000000 01101000
Now displaying the resulting hex values again we have:
02
00 EC A2 00 68
And bringing it back together:
02:00:EC:A2:00:68
So the bit-swapped version of 40:00:37:45:00:16 is 02:00:EC:A2:00:68.
Locally administered addresses for a Token Ring environment will normally begin with
4000…. and for the Ethernet environment 0200….. So, for a configuration for the
Ethernet interface, both the local address of the Ethernet card and the address of a remote
Token Ring box, both addresses will typically begin with 0200….., and if the same
configuration were to be implemented on a Token Ring interface, both addresses will
typically begin with 4000….