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--- ne:cisco [2026/06/16 09:04] – [Router] admin
+++ ne:cisco [2026/07/05 13:49] (aktuell) – [DHCP] admin
@@ Zeile 85: / Zeile 85: @@
 https://community.cisco.com/t5/switching/cisco-ios-dhcp-server-classless-static-routes-on-dhcp-clients/td-p/1783721
+== Anatomy of an Option 121 Packet ==
+Option 121 data is sent as a string of hexadecimal bytes. It format follows a strict pattern for each route:
+  - **Width (1 byte)**: The subnet mask in CIDR notation (e.g., 24 for a 255.255.255.0 mask).
+  - **Destination IP (variable length)**: The target network. \\ Trick: It only includes the bytes required by the subnet mask. If it's a /24, it sends 3 bytes. If it's a /8, it only sends 1 byte!
+  - **Router IP (4 bytes)**: The gateway address that knows how to get to that destination.
+  - Cisco supports up to 10 routes, they are just concatenated together
+**Example: **
+You want to tell a client: "To get to network 10.0.0.0/8, use the gateway 192.168.1.254."\\
+The hex payload would look like this:
+0A C0 A8 01 FE
+    > 08: The subnet mask (/8).
+    > 0A: The destination network (10 in hex). Because it's a /8, it only needs one byte.
+    > C0 A8 01 FE: The gateway IP (192.168.1.254 in hex).
 === DHCP-lease erneuern ===