Objectives
The simulator ticks each one as soon as the network meets it.
On each spine, set AS 65000 and a router ID, enable ipv4-unicast, create group "leaves" and add both leaves as neighbors.
On each leaf, set its AS, enable ipv4-unicast, create group "spines" and add both spines.
Leaves: export only their host subnet (prefix-set + policy "export-local") and import everything ("accept-all").
Spines: import and export everything with "accept-all", so each leaf’s subnet reaches the other leaf.
Ping PC2 from PC1.
Before you start
For eBGP sessions without policies SR Linux sets ebgp-default-policy import-reject-all and export-reject-all to true: the session is established but exchanges nothing. A policy with default-action policy-result accept passes everything. Spines must export what they learned, or the leaves never hear about each other.
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
SR Linux eBGP: rejected in both directions until a policy allows it
SR Linux protects eBGP sessions by default: with no import policy every received route is rejected, and with no export policy nothing is advertised. The session is Established, yet no route moves until routing policies say what is allowed.
