Exercise 2: Scale-out cost
Add a new loopback prefix 10.99.0.3/32 on leaf3 (OSPF: add it on lo, already in area 0;
BGP: also "network 10.99.0.3/32"). Compare the counter diffs. What would a whole leaf4 cost?

Answer
OSPF: leaf3 re-originates its Router LSA, every copy of the map is updated (lsa_updates +1 on all 5)
and every router runs SPF (+1 on all 5) for one new /32.
BGP: one UPDATE per session (12 in total), +1 prefix everywhere, no recompute anywhere.
Both twins end up with 2 ECMP next hops to 10.99.0.3/32 on leaf1.
A real leaf4: in OSPF it adds a new LSA AND changes both spines' Router LSAs, on every router, and
every router recomputes. In BGP it's one "neighbor eth3 interface peer-group FABRIC" line per spine
(episode 1, exercise 1) and the new prefixes ride normal UPDATEs.

Reproduce it: sudo sh solutions/exercise2/run.sh   (adds, counts, then removes)

Measured on camera (GNS3, 10/18):
router         lsa_updates           lsdb_lsas          rib_routes            spf_runs
spine1            106 (+1)              5 (+0)              9 (+1)             46 (+1)
spine2            106 (+1)              5 (+0)              9 (+1)             51 (+1)
leaf1             106 (+1)              5 (+0)             10 (+1)             53 (+1)
leaf2             106 (+1)              5 (+0)             10 (+1)             53 (+1)
leaf3             106 (+1)              5 (+0)             10 (+1)             47 (+1)
router        bgp_prefixes    bgp_updates_rcvd    bgp_updates_sent          rib_routes
spine1              8 (+1)             69 (+3)             48 (+3)              8 (+1)
spine2              8 (+1)            100 (+3)             93 (+3)              8 (+1)
leaf1               9 (+1)             60 (+2)             94 (+2)             10 (+1)
leaf2               9 (+1)             42 (+2)             42 (+2)             10 (+1)
leaf3               9 (+1)             42 (+2)             42 (+2)             10 (+1)
The kit on containerlab gave the same deltas.
