[rbridge] Updated charter

[Erik Nordmark]

Michael Smith wrote:

>>The solutions that have been discussed will replace the L2 
>>headers (at least in some cases, and encapsulate in another 
>>L2 header in some cases), and not decrement the L3 TTL, which 
>>is different than a bridge (which doesn't replace the L2 
>>header) and a router (which decrements TTL).
> 
> 
> Some specific examples may help clarify, but the above statement sounds like
> the traditional bridge of yore i.e. bridges with ethernet and token ring
> interfaces that swap MAC headers to the appropriate canonical format and
> encapsulating bridging packets over ATM and Frame Relay using RFC1483 and
> RFC1490.

I guess there is a difference between the theory of bridges, captured in 
IEEE standards, and what products actually do. I don't think the IEEE 
standards talk about what bridges between e.g. Ethernet and Token Ring 
do, but I recall products doing somethings like handling bit-order 
issues with the addresses in arp packets, and the need to fragment IP 
packets due to the different MTUs.

Radia's rbridge draft (I think) talks about optimizations for IP where 
the IP packet would transit a cloud of rbridges unmodified, but where 
the L2 header might be different on exit than on entry. This isn't a 
problem for IP, since IP doesn't look at the L2 header, but can't be 
applied to non-IP (aka unknown to the rbridge) protocols.

    Erik