Hmmm. On the one hand you say: "the numbers being thrown around for scale-up networks seem to be a couple of thousand nodes at most"
and on the other hand you say: "that would require Ethernet addresses to be the endpoint addresses and they don't have the hierarchical addressing that people want in network layer addresses. While that might work for a small scale, it will have difficulty scaling to large deployments". So, are these small networks with a few thousand nodes or massive networks with hundreds of thousands of nodes? SUNH seems to be addressing the former. I'm confused :-( ---------------------------------------- Jan 16, 2026 2:40:10 p.m. Tom Herbert <[email protected]>: > On Fri, Jan 16, 2026 at 11:08 AM Bill Gage <[email protected]> wrote: >> >> Hello Tom - >> >> Sorry if I am being a bit dense, but ... routing in datacentres replaced >> Ethernet switching to provide capabilities such as fast reroute, >> improved scalability, improved network management, etc which SUNH >> doesn't seem to address. >> >> If SUNH is only about reducing packet overheads, what value does SUNH >> provide versus using Ethernet without *any* network header? > > Hi Bill, > > Yes, there are some advocates who want to do that, but that would > require Ethernet addresses to be the endpoint addresses and they don't > have the hierarchical addressing that people want in network layer > addresses. While that might work for a small scale, it will have > difficulty scaling to large deployments (it's quite possible people > could end up rediscovering why network layer addresses were needed in > the first place :-) ). Basically, in the datacenter we want the > advantages and ubiquity of IP without the overhead . > > The other problem is that the Ethernet header isn't sufficient. There > are four fields we need from the network layer header: Traffic Class > including ECN, Hop Limit as a safeguard against routing loops, Flow > label for ECMP, and Next Protocol so we can demux different transport > protocols over the same EtherType. These fields can fit in a four byte > header. What we don't need are things like version numbers, flags, and > payload length. > > Tom > >> >> /bill >> >> On 2026-01-15 2:57 p.m., Tom Herbert wrote: >>> On Thu, Jan 15, 2026 at 11:27 AM Bill Gage <[email protected]> wrote: >>>> >>>> Please excuse my ignorance, but ... modern Ethernet switches have MAC >>>> address table sizes on the order of hundreds of thousands of entries. >>>> Building a local switched (not routed) network using a hierarchy of >>>> Ethernet switches appears to be a common practice. >>> >>> Hi Bill, >>> >>> Larger networks, like in hyperscalers, are more likely to be L3 >>> switched than spanning tree. There is also a know problem with >>> Ethernet that it lacks a hop limit. >>> >>>> >>>> So what problem does SUNH solve? >>> >>> 1. It reduces the size of the network layer header to reduce >>> on-the-wire overhead >>> 2. A smaller address simplifies switching and address lookups >>> >>> Tom >>> >>>> >>>> /bill >>>> >>>> On 2026-01-09 5:53 p.m., Tom Herbert wrote: >>>>> On Fri, Jan 9, 2026 at 2:03 PM dave seddon <[email protected]> >>>>> wrote: >>>>>> … >>>>> >>>>> The numbers being thrown around for scale-up networks seem to be a >>>>> couple of thousand nodes at most. 16 bits nicely rounds to the power >>>>> of two and allows plenty of space to scale to reasonably large GPU >>>>> clusters. Also, for scale-up we anticipate pretty flat networks with >>>>> may two or three hops at most (justifies smaller Hop Limits in the >>>>> protocol). >>>>> >>>> >>>> >>>> >>>> _______________________________________________ >>>> Int-area mailing list -- [email protected] >>>> To unsubscribe send an email to [email protected] >> _______________________________________________ Int-area mailing list -- [email protected] To unsubscribe send an email to [email protected]
