We have competitors that are claiming that their network is superior to
ours (salesdroids to customers) because they have fewer L3 hops in their
network. I see this "fact" pop up in customer questions all the time.
I can see that L3 hops adds latency if a network is built on slow (2meg
for instance) links, but at gigabit speeds, L3 hops adds microseconds in
latency (if you use equipment that forward using hardware-assisted
forwarding, but as far as I know there are no routers out there nowadays
that doesnt).
Does anyone have a nice reference I can point to to once and for all state
that just because a customer has 6-8 L3 hops within our network (all at
gigabit speeds or higher) that doesnt automatically mean they are getting
bad performance or higher latency.
Hiding the L3 hops in a MPLS core (or other L2 switching) doesnt mean
customers are getting better performance since equipment today forwards
just as quickly on L3 as on L2.
In a commercial sense hops are seen as bad, points of failure(?) or 'distance from the middle of the internet'?. Who knows
Traceroutes aren't great at seeing whats REALLY going on.
I suspect if everyone removed all their 'hop hiding' technology traceroutes would be at least 60% longer, the latency would remain the same.
Commercial sense doesn't have to make sense... If its what your competitors use to sell service, Hide your hops 
G
Mikael Abrahamsson wrote:
Of course L3 forwarding is not by itself "bad" for the packets. However...
If you have a network with "excessive" hops (for some definition of
excessive), it probably means one or more of the following:
A) you have a poor (or at least non-elegant) network design.
B) you have more places for things to go wrong in both hardware and
software.
C) you're busy gratifying your architectural ego instead of designing
the simplest thing possible which gives you the necessary performance
and reliability.
D) you're buying so much unnecessary hardware that you are either not
not financially healthy or you're not passing on as much savings as you
could be to your customer.
Now while I'm sure that you don't fit into that definition of "excessive",
I can think of a few people who do, and they try to use that "but more L3
hops are never bad" argument.
Of course L3 forwarding is not by itself "bad" for the packets. However...
If you have a network with "excessive" hops (for some definition of
excessive), it probably means one or more of the following:
A) you have a poor (or at least non-elegant) network design.
If your L3 topology is well aligned with your L1 topology, you usually
end up with more hops. The less intermediate gear, like SONET you
use but do L3 instead, the more L3 hops you have.
B) you have more places for things to go wrong in both hardware and
software.
This is specifically true for the hop-hiders using MPLS or other mostly
pointless multihop recursive switching systems.
C) you're busy gratifying your architectural ego instead of designing
the simplest thing possible which gives you the necessary performance
and reliability.
Hop-hiding is usually going the other way from the simplest thing.
D) you're buying so much unnecessary hardware that you are either not
not financially healthy or you're not passing on as much savings as you
could be to your customer.
Eliminating n+1 kinds of gear and replacing it with a smaller number of
different kind of boxes makes your network simpler and saves nicely
on OPEX. Might be somewhat more CAPEX intensive on the start but
not by a large margin.
Now while I'm sure that you don't fit into that definition of "excessive",
I can think of a few people who do, and they try to use that "but more L3
hops are never bad" argument.
This would translate to that "hops are bad", regardless of the layer. Many
people
mess with L4 to L7 generating unneccesary hops on application protocols.
These usually seem to be the same growd that does other hiding things.
Pete
If your L3 topology is well aligned with your L1 topology, you usually
end up with more hops. The less intermediate gear, like SONET you
use but do L3 instead, the more L3 hops you have.
This is exactly what we do, we run L3 pretty much directly on the fiber
with some OEO-repeaters in between, therefore we display much of our
infrastructure in a traceroute. We can do a L2 hop instead, that will
probably make things less efficient in some cases and will hide the
underlying infrastructure, but will make customers happy. I don't like to
do silly technical suboptimisations for cosmetical reasons.
> B) you have more places for things to go wrong in both hardware and
> software.
This is specifically true for the hop-hiders using MPLS or other mostly
pointless multihop recursive switching systems.
Quite true. I mean, either the equipment does an L2 or an L3 hop, either
way it can go wrong.