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--- notiz:dual-stack-lite-linux [2025/11/08 17:07] – angelegt clerie
+++ notiz:dual-stack-lite-linux [2025/11/20 20:09] (aktuell) – [References] clerie
@@ Zeile 1: / Zeile 1: @@
 ====== Dual Stack Lite (DS-Lite) B4 Element on Linux ======
-[[https://datatracker.ietf.org/doc/html/rfc6333|RFC6333]] specifies a so called B4 element on the CPE side. This is about this B4 element.
+[[https://datatracker.ietf.org/doc/html/rfc6333|RFC6333]] specifies a so called Basic Bridging BroadBand (B4) element on the CPE side. This is about this B4 element.
 What I write here is what I learned by figuring making [[https://git.clerie.de/clerie/nixfiles/commit/f3629c2653f311398bfa5fad876b2744ffc66b40|this NixOS configuration]].
@@ Zeile 7: / Zeile 7: @@
 It is tested against a FTTB connection from [[https://www.netcologne.de/privatkunden/|Netcologne]].
+===== WAN Interface =====
+I expect that you have a WAN interface with IPv6 working already.
+This can be a PPPoE tunnel or anything else.
 ===== Encapsulation =====
@@ Zeile 14: / Zeile 19: @@
 <code>
-ip tunnel add "${TUNNEL_INTERFACE_NAME}" mode ipip6 local "${WAN_INTERFACE_ADDRESS}" remote "${AFTR_ADDRESS}"
+ip tunnel add "${TUNNEL_INTERFACE_NAME}" mode ipip6 local "${WAN_INTERFACE_ADDRESS}" remote "${AFTR_ADDRESS}" encaplimit none
 </code>
+==== Tunnel Encapsulation Limit ====
+Generic Packet Tunneling in IPv6 allows setting a [[https://www.rfc-editor.org/rfc/rfc2473#section-4.1.1|Tunnel Encapsulation Limit]].
+That limit is passed as Destination Option for IPv6.
+Unfortunately to AFTR of my provider Netcologne just throws away packets that contain Destination Options, except they carry ICMP.
+The Linux Kernel is setting a Tunnel Encapsulation Limit by default.
+As a workaround one can set ''encaplimit none'' at creation of the tunnel.
+That way, there are no Destination Options set and IPv4 is encapsulated directly.
 ===== AFTR Address Discovery =====
@@ Zeile 32: / Zeile 48: @@
 ===== AFTR Name Discovery =====
-You can request the AFTR name on the WAN interface with DHCP6 using the ''aftr_name'' option.
+You can request the AFTR name on the WAN interface with DHCPv6 using the ''aftr_name'' option.
 With my provider Netcologne the ''aftr_name'' option was only answered while requesting a prefix delegation along it.
@@ Zeile 51: / Zeile 67: @@
   * aftr10.netcologne.de
+===== References =====
+  * [[https://git.archive.openwrt.org/?p=openwrt.git;a=blob;f=package/network/ipv6/ds-lite/files/dslite.sh;h=a7e0a10542b856aa640fd438558cfffe524d6c93;hb=575107bc975a3fb23ebc896e8035b043706be0b2|OpenWrt DS-Lite implementation]]
+  * [[https://www.netcologne.de/cms/api/fileadmin/user_upload/privatkunden/pdf/weitere-formulare/Schnittstellenbeschreibung.pdf|Netcologne Schnittstellenbeschreibung]]