V4 via V6 and IGP routing protocols

Mon Apr 4 14:06:25 UTC 2022

On 4/4/22 15:45, Masataka Ohta wrote:

>
> MPLS with nested labels, which is claimed to scale because
> nesting represents route hierarchy, just does not scale because
> source hosts are required to provide nested labels, which
> means the source hosts have the current most routing table at
> destinations, which requires flat routing without hierarchy or on
> demand, that is, flow driven, look up of detailed routing tables
> of destinations at a distance.

This detail is limited to PE devices (ingress/egress). You don't need to 
carry a BGP table in the P devices (core), as only label swapping is 
required.

Fair point, it is a little heavy for an edge box, but I imagine nearly 
any feature of consequence is going to be high-touch, high-impact, for 
the edge.

Those who have solved this problem with SR can comment, as we don't run it.

We did experiment with IS-IS hierarchy (L1 within the data centre and L2 
between them), but Route Leaking (copying L2 routes into L1) was a 
requirement in order to facilitate FEC creation (/32 for IPv4, /128 for 
IPv6). In the end, having a flat L2 domain was just simpler. It's been 
years, and on today's hardware, we've never ran into an issue carrying 
thousands of IS-IS IPv4/IPv6 routes this way.

Mark.