I just wanted to see if there was anyone who could clear a few things up for
me about Source Route Bridging and its many variations.
What I am mainly trying to clear up is MAC addresses that are transmitted to
the destination over these networks. Here we go:
Transparent Bridging [TB]
MAC Address is NEVER changed from end to end. The destination sees
the original source MAC address when the packet arrives.
Source Route Bridging [SRB]
If the RII is set to 0, then the destination sees the original
source MAC address when the packet arrives.
If, however, the RII is set to 1, then the first bit of the original
source address is modified and the destination sees this modified
version of the original source's MAC address.
Example.
Original MAC Address (HEX) 00-50-DA-84-4B-E1
(Binary) 0000
0000........
Modified MAC Address (HEX) 80-50-DA-84-4B-E1
(Binary) 1000
0000........
Source Route Transparent Bridging [SRT]
Ethernet hosts/Non Source Route Capable Hosts
MAC is NEVER modified. Destination sees the original source
MAC Address.
Token Ring/Source Route Bridge hosts
Same as the SRB example about with RII 0 or 1.
Source Route Translational Bridging [SR/TLB]
Token Ring to Token Ring (Source Route Capable)
Same as the SRB example about with RII 0 or 1.
Ethernet to Ethernet
MAC is NEVER modified. Destination sees the original source
MAC Address.
Token Ring to Ethernet OR Ethernet to Token Ring
MAC Address is converted to the correct version for each
side:
Example
Token Ring MAC (Hex) 0 0
5 0 D A 8 4 4 B E 1
Token Ring MAC (Binary) 0000 0000 - 0101
0000 - 1101 1010 - 1000 0100 - 0100 1011 - 1110 0001
Ethernet MAC (Hex) 0 0
0 A 5 B 2 1 D 2 8 7
Ethernet MAC (Binary) 0000 0000 - 0000
1010 - 0101 1011 - 0010 0001 - 1101 0010 - 1000 0111
Remote Source Route Bridging [RSRB]
Same as SRB with the RII set to 0 or 1 issue.
Data Link Switching + [DLSw+]
This is where I have the most confusion. If the RIF is regenerated
at each step, I am not sure if the source and destination in the packets are
modified. If the MAC's are modified then the MAC at the destination is for
the last interface of the last router that touched the packet. If these
devices act like normal bridges, the only thing you would have to worry
about is the RII bit as with SRB.
That's it, I hope this was clear and someone can straighten up anything I
might have screwed up. Thanks!
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