Objectives
The simulator ticks each one as soon as the network meets it.
On SPINE1 and SPINE2, run router bgp 65000 and peer with both leaves.
On LEAF1 (AS 65101) and LEAF2 (AS 65102), peer with both spines and advertise the host subnet.
Check show ip bgp summary on a spine: both sessions are Estab.
LEAF1 learns 192.168.2.0/24 as an eBGP route.
Ping PC2 from PC1.
Before you start
In an eBGP leaf-spine design each leaf has its own AS and the spines share one. The AS path stops loops: a spine never accepts a route that already carries AS 65000. EOS takes the router ID under router bgp and networks in prefix form.
Concept
Leaf-spine fabrics with an eBGP underlay
A data-center fabric connects every leaf switch to every spine, so any two hosts are exactly two hops apart and every leaf has as many equal paths as there are spines. Many fabrics run eBGP on every link: each leaf gets its own AS, and the spines share one.
Concept
eBGP: exchanging routes between autonomous systems
BGP connects networks run by different organisations (autonomous systems). Two routers in different ASes form an eBGP session over TCP port 179 and advertise only the prefixes they choose, each tagged with the AS path it has crossed.
