我试图理解为什么最近的 Linux 内核中存在 ipv6 默认路由到环回
::/0 :: !n -1 1 4 lo
是为了防止循环吗？为什么下面的输出中有两条这样的路由？
root@ubuntu:/# ip -6 route show table all
fd00:1::/64 dev eth0 proto kernel metric 256 expires 2591833sec
fd00:1::/64 dev eth1 proto kernel metric 256 expires 2591833sec
fd00:2::/64 via fd00:1::1 dev eth0 metric 1
fe80::/64 dev eth0 proto kernel metric 256
fe80::/64 dev eth1 proto kernel metric 256
default via fe80::21f:12ff:fe31:5600 dev eth0 proto kernel metric 1024 expires 1309sec
default via fe80::21f:12ff:fe31:5600 dev eth1 proto kernel metric 1024 expires 1309sec
unreachable default dev lo table unspec proto kernel metric -1 error -101
local ::1 via :: dev lo table local proto none metric 0
local fd00:1::250:56ff:fe8a:596a via :: dev lo table local proto none metric 0
local fd00:1::250:56ff:fe8a:596b via :: dev lo table local proto none metric 0
local fd00:1::18ec:2a1:3b2e:8302 via :: dev lo table local proto none metric 0
local fd00:1::59b1:42d0:b380:a32d via :: dev lo table local proto none metric 0
local fe80::250:56ff:fe8a:596a via :: dev lo table local proto none metric 0
local fe80::250:56ff:fe8a:596b via :: dev lo table local proto none metric 0
ff00::/8 dev eth0 table local metric 256
ff00::/8 dev eth1 table local metric 256
unreachable default dev lo table unspec proto kernel metric -1 error -101
root@ubuntu:/# route -nA inet6
Kernel IPv6 routing table
Destination Next Hop Flag Met Ref Use If
fd00:1::/64 :: UAe 256 0 1 eth0
fd00:1::/64 :: UAe 256 0 0 eth1
fd00:2::/64 fd00:1::1 UG 1 0 0 eth0
fe80::/64 :: U 256 0 0 eth0
fe80::/64 :: U 256 0 0 eth1
::/0 fe80::21f:12ff:fe31:5600 UGDAe 1024 0 0 eth0
::/0 fe80::21f:12ff:fe31:5600 UGDAe 1024 0 0 eth1
::/0 :: !n -1 1 4 lo
::1/128 :: Un 0 1 12 lo
fd00:1::250:56ff:fe8a:596a/128 :: Un 0 1 0 lo
fd00:1::250:56ff:fe8a:596b/128 :: Un 0 1 0 lo
fd00:1::18ec:2a1:3b2e:8302/128 :: Un 0 1 0 lo
fd00:1::59b1:42d0:b380:a32d/128 :: Un 0 1 0 lo
fe80::250:56ff:fe8a:596a/128 :: Un 0 1 0 lo
fe80::250:56ff:fe8a:596b/128 :: Un 0 1 0 lo
ff00::/8 :: U 256 0 0 eth0
ff00::/8 :: U 256 0 0 eth1
::/0 :: !n -1 1 4 lo
root@ubuntu:/#
输出形式
root@ubuntu:/# uname -a
Linux ubuntu 3.5.0-23-generic #35~precise1-Ubuntu SMP Fri Jan 25 17:13:26 UTC 2013 x86_64 x86_64 x86_64 GNU/Linux
答案1
正如标志!n所示，这是对 IN6ADDR_ANY 流量的拒绝。此路由条目的含义是该lo设备永远不会被用作默认路由。
此处显示的表中的等效线ip route是：
unreachable default dev lo table unspec proto kernel metric -1 error -101
（另请注意，正如手册页警告您的那样，该route命令已过时，您应该改用ip route。）