fff-layer3-vxmesh: add babel MTU filters

A VXLAN Tunnel (IPv6, without inner VLAN tag) adds 70 bytes of overhead
to each packet. To support bridging our client interfaces with an MTU of
1500, VXLAN packets require a link with an MTU of 1570.

To avoid sending too large packets to peers over a link with an MTU less
than 1570, this patch adds filters to babel to ignore routes to peers
announced over small links.

Signed-off-by: Johannes Kimmel <fff@bareminimum.eu>

src/packages/fff/fff-layer3-vxmesh/Makefile

@@ -0,0 +1,29 @@
+include $(TOPDIR)/rules.mk
+
+PKG_NAME:=fff-layer3-vxmesh
+PKG_RELEASE:=1
+
+include $(INCLUDE_DIR)/package.mk
+
+define Package/fff-layer3-vxmesh
+	SECTION:=base
+	CATEGORY:=Freifunk
+	TITLE:=Freifunk-Franken layer3 configuration for mesh via vxlan
+	URL:=http://www.freifunk-franken.de
+	DEPENDS:=+vxlan
+endef
+
+define Package/fff-layer3-vxmesh/description
+	Adds a simple configuration to connect multple routers into one layer 2
+	network via vxlan.
+endef
+
+define Build/Compile
+	# nothing
+endef
+
+define Package/fff-layer3-vxmesh/install
+	$(CP) ./files/* $(1)/
+endef
+
+$(eval $(call BuildPackage,fff-layer3-vxmesh))

src/packages/fff/fff-layer3-vxmesh/files/etc/layer3.d/60-vxmesh

@@ -0,0 +1,161 @@
+#!/bin/sh
+
+. /lib/functions.sh
+
+configure() {
+	local proto
+	local peerip
+	local otherpeers
+	local fields="
+		proto
+		port
+		vid
+		ttl
+		tos
+		mtu
+		macaddr
+		zone
+		rxcsum
+		txcsum
+		srcportmin
+		srcportmax
+		ageing
+		maxaddress
+		learning
+		rsc
+		proxy
+		l2miss
+		l3miss
+		gbp
+		tunlink
+		ipaddr
+		ip6addr
+	"
+
+	# cleanup old vxmesh and peer entries
+	uci -q delete network.vxmesh0
+	while uci -q delete network.@vxlan_peer[-1]; do :; done
+
+	# remove vxmesh0 entry from the client bridge and remove extra whitespaces
+	uci set network.client.ifname="$(uci -q get network.client.ifname | sed s/vxmesh0// | xargs)"
+
+	# reset dns to authorative
+	uci set dhcp.@dnsmasq[0].authoritative="1"
+
+	# check if a vxmesh config is available, otherwise quit
+	uci -q get gateway.@vxmesh[0] > /dev/null || return 0
+
+	# check if proto is set and probe for the correct peer ip
+	proto="$(uci -q get gateway.@vxmesh[0].proto)"
+	case "$proto" in
+		vxlan6)
+			peerip="$(uci -q get gateway.@gateway[0].peer_ip6)"
+			;;
+		vxlan)
+			peerip="$(uci -q get gateway.@gateway[0].peer_ip)"
+			;;
+		*)
+			echo "FATAL: vxmesh: option proto 'vxlan|vxlan6' required!"
+			return 1
+			;;
+	esac
+
+	# vxmesh needs a separate peer ip as the ip on the client interface ip
+	# might be shared over multiple devices
+	[ -z "$peerip" ] && {
+		echo "FATAL: vxmesh: peer_ip|peer_ip6 required!"
+		return 1
+	}
+
+	uci -q get gateway.@vxmesh[0].vid > /dev/null || {
+		echo "FATAL: vxmesh: missing vid!"
+		return 1
+	}
+
+	# copy main options over
+	uci set network.vxmesh0="interface"
+	for option in $fields; do
+		uci set network.vxmesh0."$option"="$(uci -q get gateway.@vxmesh[0]."$option")"
+	done
+
+	# exclude peerip from the local router, so packets aren't sent to itself
+	otherpeers=$(uci -q get gateway.@vxmesh[0].peer | xargs -n1 | grep -v -e "$peerip")
+
+	for peer in $otherpeers; do
+		# create peer sections
+		if ! uci -q batch > /dev/null; then
+			echo "FATAL: vxmesh: error setting up peer!"
+			echo "       peer: \"$peer\""
+			return 1
+		fi <<- EOF
+			add network vxlan_peer
+			set network.@vxlan_peer[-1].vxlan="vxmesh0"
+			set network.@vxlan_peer[-1].dst="$peer"
+		EOF
+	done
+
+	# learn routes to other peers only over babel interfaces with sufficient mtu
+	#   - according to the rfc, vxlan packets must not be fragmented by a VTEP
+	#   - the vxlan tunnel requires an mtu of 1570 when using ipv6
+	#
+	#  -> to avoid sending too large packets over an interface with too small mtu,
+	#     don't learn a route to a peer over that interface in the first place
+	babel_filter_mtu() {
+		local config="$1"
+		local otherpeers="$2"
+		local mtu
+		local ifname
+
+		case $config in
+			babelpeer*) ;;
+			wireguardpeer*) ;;
+			*) return ;;
+		esac
+
+		config_get mtu "$config" mtu
+		config_get ifname "$config" ifname
+
+		[ "${mtu:-0}" -ge "1570" ] && return
+		[ -z "${ifname}" ] && {
+			echo "WARNING: could not determine ifname from \"$config\""
+			return
+		}
+		for peer in $otherpeers; do
+			if ! uci -q batch > /dev/null; then
+				echo "FATAL: error adding babel filter for vxlan peer!"
+				echo "       peer: \"$peer\""
+				echo "       interface: \"$ifname\""
+				return 1
+			fi <<- EOF
+				add babeld filter
+				set babeld.@filter[-1].type="in"
+				set babeld.@filter[-1].ip="$peer"
+				set babeld.@filter[-1].if="$ifname"
+				set babeld.@filter[-1].addedbyautoconfig="true"
+				set babeld.@filter[-1].action="deny"
+			EOF
+		done
+	}
+
+	config_load network
+	config_foreach babel_filter_mtu interface "$otherpeers"
+
+	# with multiple routers in the network, there shouldn't be an authoritative
+	# dhcp server
+	uci set dhcp.@dnsmasq[0].authoritative="0"
+
+	# add the vxlan interface to the client bridge
+	uci set network.client.ifname="$(uci -q get network.client.ifname) vxmesh0"
+}
+
+apply() {
+	uci commit network
+	uci commit dhcp
+	uci commit babeld
+}
+
+revert() {
+	uci revert network
+	uci revert dhcp
+	uci revert babeld
+}

src/packages/fff/fff-layer3/Makefile

@@ -1,7 +1,7 @@
 include $(TOPDIR)/rules.mk
 
 PKG_NAME:=fff-layer3
-PKG_RELEASE:=8
+PKG_RELEASE:=9
 
 include $(INCLUDE_DIR)/package.mk
 
@@ -36,7 +36,7 @@ define Package/fff-layer3
 	         +mtr \
 	         +tc \
 	         +tcpdump \
-	         +vxlan
+	         +fff-layer3-vxmesh
 endef
 
 define Package/fff-layer3/description

src/packages/fff/fff-network/Makefile

@@ -1,7 +1,7 @@
 include $(TOPDIR)/rules.mk
 
 PKG_NAME:=fff-network
-PKG_RELEASE:=31
+PKG_RELEASE:=32
 
 include $(INCLUDE_DIR)/package.mk
 

src/packages/fff/fff-network/files/usr/lib/nodewatcher.d/50-clients.sh

@@ -12,7 +12,7 @@ debug "Collecting information about connected clients"
 
 client_count=0
 dataclient=""
-CLIENT_INTERFACES=$(ls "/sys/class/net/$MESH_INTERFACE/brif" | grep -v '^bat')
+CLIENT_INTERFACES=$(ls "/sys/class/net/$MESH_INTERFACE/brif" | grep -v -e '^bat' -v -e '^vxmesh')
 for clientif in ${CLIENT_INTERFACES}; do
 	cc=$(bridge fdb show br "$MESH_INTERFACE" brport "$clientif" | grep -v self | grep -v permanent -c)
 	client_count=$((client_count + cc))