Buffalo WZR-600DHP OpenWrt使用Comcast的IPv6

路由器

根據https://wiki.openwrt.org/toh/buffalo/wzr-600dhp在Buffalo WZR-600DHP上安裝OpenWrt。Buffalo路由器的好處在於brick了還能借助bootloader用tftp安裝。

我的Internet service provider爲COMCAST-7922 - Comcast Cable Communications, LLC, US，提供了4個IPv6 delegated prefix /64。

配置odhcpd的DHCPv6 relay，修改/etc/config/dhcp：

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config dhcp 'wan6'
        option dhcpv6 relay
        option ra relay
        option ndp relay
        option master 1

修改/etc/config/network。wan和wan6的bridge沒啥用，註釋掉option type 'bridge'。

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config interface 'wan'
        ......
        #option type 'bridge'

config interface 'wan6'
        ......
        #option type 'bridge'

config interface 'lan'
        ......
        option ip6assign '60'

如果不填寫ip6assign '60'的話，在連接路由器的設備上dhcpcd -6會看到：

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% sudo dhcpcd -6 wlp3s0
DUID 00:01:00:01:1d:04:34:19:d0:7e:35:f4:c6:3a
wlp3s0: IAID 35:f4:c6:3a
wlp3s0: soliciting an IPv6 router
wlp3s0: Router Advertisement from fe80::b2c7:45ff:fe75:9e90
wlp3s0: adding default route via fe80::b2c7:45ff:fe75:9e90
wlp3s0: soliciting a DHCPv6 lease
wlp3s0: fe80::b2c7:45ff:fe75:9e90: DHCPv6 REPLY missing IA Address
wlp3s0: no useable IA found in lease
wlp3s0: fe80::b2c7:45ff:fe75:9e90: DHCPv6 REPLY missing IA Address
wlp3s0: no useable IA found in lease
wlp3s0: fe80::b2c7:45ff:fe75:9e90: DHCPv6 REPLY missing IA Address
wlp3s0: no useable IA found in lease
wlp3s0: fe80::b2c7:45ff:fe75:9e90: DHCPv6 REPLY missing IA Address
wlp3s0: no useable IA found in lease
^Creceived SIGINT, stopping
wlp3s0: removing interface
dhcpcd exited

我使用的openwrt-15.05.1-ar71xx-generic-wzr-600dhp-squashfs-sysupgrade.bin比較古怪，默認禁用了eth0(lan)及eth1(wan)的IPv6。

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root@OpenWrt:~# sysctl -a | grep disable_ipv6
......
net.ipv6.conf.eth0.disable_ipv6 = 1
net.ipv6.conf.eth1.disable_ipv6 = 1
......

用sysctl把它們改成0。要持久化配置的話，修改/etc/config/firewall：

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config defaults
	options disable_ipv6 0

修改完兩個文件後/etc/init.d/network reload; /etc/init.d/dhcp reload。

筆記本電腦

我的筆記本電腦安裝Arch Linux，使用netctl、netctl-auto管理網絡。向/etc/netctl/$profile添加兩行：

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IP6=dhcp
DHCP6Client=dhcpcd

默認的DHCPv6客戶端dhclient不工作，不明原因，觀察/usr/lib/network/ip發現設置DHCP6Client即可指定DHCPv6客戶端。

之後訪問http://test-ipv6-ct.comcast.net，查看IPv6評分，10 of 10。

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Your IPv4 address on the public Internet appears to be x.x.x.x
Your IPv6 address on the public Internet appears to be x:x:x:x:x:x:x:x
Your Internet Service Provider (ISP) appears to be COMCAST-7922 - Comcast Cable Communications, LLC, US
Since you have IPv6, we are including a tab that shows how well you can reach other IPv6 sites. [more info]
Good news! Your current configuration will continue to work as web sites enable IPv6.
Your DNS server (possibly run by your ISP) appears to have IPv6 Internet access.

診斷

路由器上opkg install tcpdump，之後在筆記本電腦上mkfifo fifo; ssh root@192.168.1.1 'tcpdump -s0 -Unw - -i eth1' > fifo，另一個shell裏wireshark -ki fifo。

IPv6一直弄不好，在TUNA羣裏大家討論診斷了很久，王邈給出了很多診斷建議。小結下有這些東西：

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ip -6 a         # address
ip -6 r s t all # route
ip -6 ru        # rule
sysctl -a | grep net.ipv6.conf.$iface    # $ifame 填 eth0 eth1 br-lan br-wan 等
ip6tables -nL

注意以下值： 

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net.ipv6.conf.eth1.accept_ra = 1
net.ipv6.conf.eth1.autoconf = 1
net.ipv6.conf.eth1.disable_ipv6 = 0

怕ip6tables產生影響的話，ip6tables -F; ip6tables -P ACCEPT FORWARD。

對於OpenWrt系統，當disable_ipv6=1的時候，如果接口外面套了bridge，那麼對外發送IPv6包(如connect、sendto等syscall)找不到路由時會報告EACCES(Permision denied)；即使有路由，tcpdump也看不到有包發出去。當心套上bridge後會丟失一些錯誤信息，ip -6 a a $ip6 dev br-wan不會報錯，但ip -6 a a $ip6 dev eth1會報告EACCES(Permission denied)。

其他

之前使用D-Link DIR-860 B1，https://www.amazon.com上有打折後$30.75的。通過網頁界面安裝OpenWrt很方便，但是室友報告Steam上很多遊戲有明顯丟包。