docs: Mention RouteTableInterfacesOffset in system requirements

ENI mode creates routing tables with index `10 + eni-index`. This commit documents that and mentions that those indices are not taken by the system. Suggested-by: Chris Tarazi <chris@isovalent.com> Signed-off-by: Sebastian Wicki <sebastian@isovalent.com>
cilium · Oct 3, 2023 · 9d3976c · 9d3976c
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diff --git a/Documentation/operations/system_requirements.rst b/Documentation/operations/system_requirements.rst
@@ -461,6 +461,17 @@ filesystem to be automatically mounted when the node boots.
 If you are using systemd to manage the kubelet, see the section
 :ref:`bpffs_systemd`.
 
+Routing Tables
+==============
+
+When running in :ref:`ipam_eni` IPAM mode, Cilium will install per-ENI routing
+tables for each ENI that is used by Cilium for pod IP allocation.
+These routing tables are added to the host network namespace and must not be
+otherwise used by the system.
+The index of those per-ENI routing tables is computed as
+``10 + <eni-interface-index>``. The base offset of 10 is chosen as it is highly
+unlikely to collide with the main routing table which is between 253-255.
+
 Privileges
 ==========
 

diff --git a/Documentation/spelling_wordlist.txt b/Documentation/spelling_wordlist.txt
@@ -33,6 +33,7 @@ Dinan
 Dockerfile
 Dockerfiles
 Donenfeld
+ENI
 FIt
 Fastabend
 Fosdem