[c-nsp] LDPv6 Census Check

Andrey Kostin ankost at podolsk.ru
Fri Jun 12 17:12:46 UTC 2020

Saku Ytti писал 2020-06-12 12:10:
> On Fri, 12 Jun 2020 at 18:52, David Sinn <dsinn at dsinn.com> wrote:
>> Unless you want ECMP then it VERY much matters. But I guess since we 
>> are only talking about theoretical instead of building an actual 
>> practical network, it doesn't matter.
> Well blatantly we are, because in the real world most of the value of
> MPLS tunnels is not available as IP tunnels. Again technically
> entirely possible to replace MPLS tunnels with IP tunnels, just
> question how much overhead you have in transporting the tunnel key and
> how wide they are.
> Should we design a rational cost-efficient solution, we should choose
> the lowest overhead and narrowest working keys.

Sorry for jumping in in the mddle of discussion, as a side note, in case 
of IPIP tunneling, shouldn't another protocol type be utilized in MAC 
header? As I understand, in VXLAN VTEP ip is dedicated for this purpose, 
so receiving a packet with VTEP DST IP already means "decapsulate and 
lookup the next header". But in traditional routers loopback IPs are 
used for multiple purposes and usually receiving a packet with lo0 IP 
means punt it to control plane. Isn't additional differentiator is 
needed here to tell a router which type of action it has to do? Or, as 
alternative, if dedicated stack of IPs is used for tunneling, then 
another lookup table is needed for it, isn't it? And now looks like we 
are coming to the header structure and forwarding process similar that 
we already have in MPLS, only with different label format. Please  
correct me if I went off track somewhere in this logical chain.

To David's point about ECMP I'd like to mention that in WAN networks 
number of diverse paths is always limited, so having multiple links 
taking same path doesn't make much sense. With current economics 4x10G 
and 1x100G are usually close from price POV. Obviously, there are 
different situations when multiple links are the only option, but how 
many, usually 4-8. Sure if you need multiple 400G then there is 
currently no option to go to higher speeds, but that's more DC use case 
than WAN network. So ECMP in WAN network isn't that big scale problem 
imho, also there are existing and proposed solutions, like SR, for it.

Kind regards,

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