本文原创：中国科学技术大学 张焕杰
修改时间：2017.12.04
自己建立根DNS服务器，可以减少查询的延迟，少受外部网络的影响。
我使用的是CentOS 6，其他系统也类似。安装bind软件作为DNS服务器。
设置好以太网口的IPv4/v6地址，能正常上网即可。
将需要劫持的根DNS IP地址设置在 lo接口。我劫持了13个根DNS，使用如下命令
ip addr add 198.41.0.4/32 dev lo
ip addr add 2001:503:ba3e::2:30/128 dev lo
ip addr add 199.9.14.201/32 dev lo
ip addr add 2001:500:200::b/128 dev lo
ip addr add 192.33.4.12/32 dev lo
ip addr add 2001:500:2::c/128 dev lo
ip addr add 199.7.91.13/32 dev lo
ip addr add 2001:500:2d::d/128 dev lo
ip addr add 192.203.230.10/32 dev lo
ip addr add 2001:500:a8::e/128 dev lo
ip addr add 192.5.5.241/32 dev lo
ip addr add 2001:500:2f::f/128 dev lo
ip addr add 192.112.36.4/32 dev lo
ip addr add 2001:500:12::d0d/128 dev lo
ip addr add 198.97.190.53/32 dev lo
ip addr add 2001:500:1::53/128 dev lo
ip addr add 192.36.148.17/32 dev lo
ip addr add 2001:7fe::53/128 dev lo
ip addr add 192.58.128.30/32 dev lo
ip addr add 2001:503:c27::2:30/128 dev lo
ip addr add 193.0.14.129/32 dev lo
ip addr add 2001:7fd::1/128 dev lo
ip addr add 199.7.83.42/32 dev lo
ip addr add 2001:500:9f::42/128 dev lo
ip addr add 202.12.27.33/32 dev lo
ip addr add 2001:dc3::35/128 dev lo
vi /etc/named.conf修改配置，仅仅修改了默认文件的 listen-on listen-on-v6 allow-query recursion zone等很少的地方，增加了zone root-servers.net
options {
listen-on port 53 { any; };
listen-on-v6 port 53 { any; };
directory "/var/named";
dump-file "/var/named/data/cache_dump.db";
statistics-file "/var/named/data/named_stats.txt";
memstatistics-file "/var/named/data/named_mem_stats.txt";
allow-query { any; };
recursion no;
dnssec-enable yes;
dnssec-validation yes;
/* Path to ISC DLV key */
bindkeys-file "/etc/named.iscdlv.key";
managed-keys-directory "/var/named/dynamic";
};
logging {
channel default_debug {
file "data/named.run";
severity dynamic;
};
};
zone "." IN {
type master;
file "root.zone";
};
zone "ROOT-SERVERS.NET." IN {
type master;
file "root-servers.net.zone";
};
include "/etc/named.rfc1912.zones";
include "/etc/named.root.key";
编辑 /var/named/root-servers.net.zone文件(之前我没有加这个域，会有问题，原因可以参见 这里的Root Server Glue and BIND9)，内容为：
$TTL 1D
@ IN SOA @ fake.root. (
1 ; serial
1D ; refresh
1H ; retry
1W ; expire
3H ) ; minimum
IN NS a.root-servers.net.
IN NS b.root-servers.net.
IN NS c.root-servers.net.
IN NS d.root-servers.net.
IN NS e.root-servers.net.
IN NS f.root-servers.net.
IN NS g.root-servers.net.
IN NS h.root-servers.net.
IN NS i.root-servers.net.
IN NS j.root-servers.net.
IN NS k.root-servers.net.
IN NS l.root-servers.net.
IN NS m.root-servers.net.
A.ROOT-SERVERS.NET. A 198.41.0.4
A.ROOT-SERVERS.NET. AAAA 2001:503:ba3e::2:30
B.ROOT-SERVERS.NET. A 199.9.14.201
B.ROOT-SERVERS.NET. AAAA 2001:500:200::b
C.ROOT-SERVERS.NET. A 192.33.4.12
C.ROOT-SERVERS.NET. AAAA 2001:500:2::c
D.ROOT-SERVERS.NET. A 199.7.91.13
D.ROOT-SERVERS.NET. AAAA 2001:500:2d::d
E.ROOT-SERVERS.NET. A 192.203.230.10
E.ROOT-SERVERS.NET. AAAA 2001:500:a8::e
F.ROOT-SERVERS.NET. A 192.5.5.241
F.ROOT-SERVERS.NET. AAAA 2001:500:2f::f
G.ROOT-SERVERS.NET. A 192.112.36.4
G.ROOT-SERVERS.NET. AAAA 2001:500:12::d0d
H.ROOT-SERVERS.NET. A 198.97.190.53
H.ROOT-SERVERS.NET. AAAA 2001:500:1::53
I.ROOT-SERVERS.NET. A 192.36.148.17
I.ROOT-SERVERS.NET. AAAA 2001:7fe::53
J.ROOT-SERVERS.NET. A 192.58.128.30
J.ROOT-SERVERS.NET. AAAA 2001:503:c27::2:30
K.ROOT-SERVERS.NET. A 193.0.14.129
K.ROOT-SERVERS.NET. AAAA 2001:7fd::1
L.ROOT-SERVERS.NET. A 199.7.83.42
L.ROOT-SERVERS.NET. AAAA 2001:500:9f::42
M.ROOT-SERVERS.NET. A 202.12.27.33
M.ROOT-SERVERS.NET. AAAA 2001:dc3::35
注意这个文件需要对named可读。
cd /var/named
wget http://www.internic.net/domain/root.zone
使用iptables对外开放udp/tcp 53端口，注意IPv4/IPv6的都要允许。
service named start
dig @127.0.0.1 com. ns
延迟应该是0ms
劫持路由可以使用静态路由，也可以使用BGP动态路由。
以静态路由为例，只要在交换机上把13个根DNS IP的路由指向该Linux服务器即可。
我使用ExaBGP动态劫持，exabgp.conf配置为
neighbor 202.38.64.126 {
local-address 202.38.64.12;
peer-as 45081;
local-as 65500;
router-id 202.38.64.12;
static {
route 198.41.0.4/32 next-hop 202.38.64.12;
route 2001:503:ba3e::2:30/128 next-hop 2001:da8:d800::12;
route 199.9.14.201/32 next-hop 202.38.64.12;
route 2001:500:200::b/128 next-hop 2001:da8:d800::12;
route 192.33.4.12/32 next-hop 202.38.64.12;
route 2001:500:2::c/128 next-hop 2001:da8:d800::12;
route 199.7.91.13/32 next-hop 202.38.64.12;
route 2001:500:2d::d/128 next-hop 2001:da8:d800::12;
route 192.203.230.10/32 next-hop 202.38.64.12;
route 2001:500:a8::e/128 next-hop 2001:da8:d800::12;
route 192.5.5.241/32 next-hop 202.38.64.12;
route 2001:500:2f::f/128 next-hop 2001:da8:d800::12;
route 192.112.36.4/32 next-hop 202.38.64.12;
route 2001:500:12::d0d/128 next-hop 2001:da8:d800::12;
route 198.97.190.53/32 next-hop 202.38.64.12;
route 2001:500:1::53/128 next-hop 2001:da8:d800::12;
route 192.36.148.17/32 next-hop 202.38.64.12;
route 2001:7fe::53/128 next-hop 2001:da8:d800::12;
route 192.58.128.30/32 next-hop 202.38.64.12;
route 2001:503:c27::2:30/128 next-hop 2001:da8:d800::12;
route 193.0.14.129/32 next-hop 202.38.64.12;
route 2001:7fd::1/128 next-hop 2001:da8:d800::12;
route 199.7.83.42/32 next-hop 202.38.64.12;
route 2001:500:9f::42/128 next-hop 2001:da8:d800::12;
route 202.12.27.33/32 next-hop 202.38.64.12;
route 2001:dc3::35/128 next-hop 2001:da8:d800::12;
}
}
从其他DNS服务器（当然是路由受劫持影响的）上测试:
ping a.root-servers.net.
dig @a.root-servers.net
延迟应该为0ms
根DNS服务器中，CERNET已经对除了h.root-servers.net之外的做了镜像（劫持），所以我们仅仅对 以下14个IP地址进行劫持
ip addr add 198.97.190.53/32 dev lo
ip addr add 2001:503:ba3e::2:30/128 dev lo
ip addr add 2001:500:200::b/128 dev lo
ip addr add 2001:500:2::c/128 dev lo
ip addr add 2001:500:2d::d/128 dev lo
ip addr add 2001:500:a8::e/128 dev lo
ip addr add 2001:500:2f::f/128 dev lo
ip addr add 2001:500:12::d0d/128 dev lo
ip addr add 2001:500:1::53/128 dev lo
ip addr add 2001:7fe::53/128 dev lo
ip addr add 2001:503:c27::2:30/128 dev lo
ip addr add 2001:7fd::1/128 dev lo
ip addr add 2001:500:9f::42/128 dev lo
ip addr add 2001:dc3::35/128 dev lo
为了能在named进程正常时发布路由，异常时自动撤回路由，增加了脚本
/var/named/healthcheck.sh
#!/bin/bash
status=0
while true; do
dig +time=1 @127.0.0.1 a.root-servers.net > /dev/null 2>/dev/null
newstatus=$?
if [ $newstatus -eq 0 ]; then
newstatus=1
else
newstatus=0
fi
# echo status $status newstatus $newstatus
if [ $status -eq 0 ] ; then
if [ $newstatus -eq 1 ]; then # service up
status=1
echo announce route 198.97.190.53/32 next-hop 202.38.64.12
echo announce route 2001:503:ba3e::2:30/128 next-hop 2001:da8:d800::12
echo announce route 2001:500:200::b/128 next-hop 2001:da8:d800::12
echo announce route 2001:500:2::c/128 next-hop 2001:da8:d800::12
echo announce route 2001:500:2d::d/128 next-hop 2001:da8:d800::12
echo announce route 2001:500:a8::e/128 next-hop 2001:da8:d800::12
echo announce route 2001:500:2f::f/128 next-hop 2001:da8:d800::12
echo announce route 2001:500:12::d0d/128 next-hop 2001:da8:d800::12
echo announce route 2001:500:1::53/128 next-hop 2001:da8:d800::12
echo announce route 2001:7fe::53/128 next-hop 2001:da8:d800::12
echo announce route 2001:503:c27::2:30/128 next-hop 2001:da8:d800::12
echo announce route 2001:7fd::1/128 next-hop 2001:da8:d800::12
echo announce route 2001:500:9f::42/128 next-hop 2001:da8:d800::12
echo announce route 2001:dc3::35/128 next-hop 2001:da8:d800::12
fi
fi
if [ $status -eq 1 ] ; then
if [ $newstatus -eq 0 ]; then # service down
status=0
echo withdraw route 198.97.190.53/32
echo withdraw route 2001:503:ba3e::2:30/128
echo withdraw route 2001:500:200::b/128
echo withdraw route 2001:500:2::c/128
echo withdraw route 2001:500:2d::d/128
echo withdraw route 2001:500:a8::e/128
echo withdraw route 2001:500:2f::f/128
echo withdraw route 2001:500:12::d0d/128
echo withdraw route 2001:500:1::53/128
echo withdraw route 2001:7fe::53/128
echo withdraw route 2001:503:c27::2:30/128
echo withdraw route 2001:7fd::1/128
echo withdraw route 2001:500:9f::42/128
echo withdraw route 2001:dc3::35/128
fi
fi
sleep 1
done
然后把 /etc/exabgp.conf修改为
neighbor 202.38.64.126 {
local-address 202.38.64.12;
peer-as 45081;
local-as 65500;
router-id 202.38.64.12;
process service-dns {
run /var/named/healthcheck.sh;
}
}
定期下载root.zone文件，有更新时重启named服务即可。
建立 /var/named/Makefile:
all:
wget -O root.zone http://www.internic.net/domain/root.zone
chgrp named *
/sbin/service named configtest
/sbin/service named restart
git commit -a -m `date +"%F_%T"`
增加如下crontabl
15 * * * * cd /var/named && make
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