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README.md

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+# etherip-kmod
+
+Out-of-tree Linux kernel module for RFC3378 EtherIP over IPv6 endpoints.
+
+The module registers a rtnetlink link kind named `etherip6`.  A companion
+`etherip6ctl` helper is included because stock iproute2 does not know how to
+encode this module's private tunnel attributes.
+
+## Build
+
+On Arch Linux, install headers matching the kernel you will load into:
+
+```sh
+sudo pacman -S linux-headers
+make
+```
+
+If you need to build against a specific headers tree:
+
+```sh
+make KDIR=/usr/lib/modules/$(uname -r)/build
+```
+
+## Load
+
+```sh
+sudo insmod etherip6.ko
+```
+
+## Create a Tunnel
+
+```sh
+sudo ./etherip6ctl add eip0 local 2001:db8:1::1 remote 2001:db8:1::2
+sudo ip link set eip0 up
+sudo ip addr add 192.0.2.1/30 dev eip0
+```
+
+For link-local IPv6 endpoints, specify the egress interface:
+
+```sh
+sudo ./etherip6ctl add eip0 local fe80::1 remote fe80::2 link eth0
+```
+
+Delete the device with:
+
+```sh
+sudo ./etherip6ctl del eip0
+```
+
+## Fragmentation
+
+The transmit path permits local IPv6 fragmentation for encapsulated EtherIP
+packets that exceed the outer path MTU.  This lets a larger inner Ethernet
+frame be split into multiple outer IPv6 fragments by the local host.
+
+You can still set a smaller tunnel MTU when you want to avoid IPv6 fragments:
+
+```sh
+sudo ip link set eip0 mtu 1444
+```
+
+For a 1500-byte outer link, 1444 leaves room for the 40-byte IPv6 header,
+2-byte EtherIP header, and 14-byte Ethernet header carried inside EtherIP.
+
+## Wire Format
+
+The outer IPv6 packet uses Next Header 97.  The EtherIP header is the RFC3378
+two-byte version/reserved field with version 3, followed by the complete
+Ethernet frame.