[Irtf-rr] RE: Differentiated Routing, not only plain rambo-SPF

[Ayyasamy, Senthilkumar (UMKC-Student)]

> I am really surprised that the need for having several 
> routing table is a big (scalability) issue:
> (BTW:Logically it takes separate routing tables, one per 
> DSCP. But you may as well maintain one routing table
>  and search the next hop entry also based on the DSCP)
> IMO stateless DiffRout-Forwarding is more scalable than MPLS or RSVP.
  Yes diffserv forwarding is less stateful when compared to MPLS 
or RSVP. But that has nothing to do with scalability problems in maintaining 
multiple routing tables. 
There are scalability issues wrt single routing table itself. People are still 
working on scalable solutions for mimizing the overhead, wrt adding mechanisms 
like accounting and other valued added measurement functions, which requires 
processing of pkts at line rate. So i am guessing, scalablity associated with 
multiple routing tables, will be a long shot.

See again you have started with diffrout, then it was changed to diffser-aware-TE 
and now mechanisms for basic diffserv arch. 

> However,if the size of the routing table is an issue, then 
> why wasn't it an issue so far:
> Each ingress node needs to know the egress node before 
> setting up the respective next hop entry in the routing table.
> So why doesn't the IP header contain a field for the 
> destination router address. It would allow to keep the routing tables
> small: one single next hop entry w.r.t. each destination 
> router would be sufficient.
> Of course, it would be rediculous to expect any change in 
> IPv4. But why wasn't this an issue for IPv6 ?
> When IPv6 was born, I guess there have already been routing 
> tables of respectful size.
> Can anyone tell me?

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