参考
https://unix.stackexchange.com/questions/348327/using-ip-what-does-m-down-mean
www.policyrouting.org/iproute2.doc.html#ss9.1
简介
是指上一级的接口的状态。
实例
4: erspan0@NONE: <BROADCAST,MULTICAST> mtu 1450 qdisc noop state DOWN mode DEFAULT group default qlen 1000
link/ether 00:00:00:00:00:00 brd ff:ff:ff:ff:ff:ff promiscuity 0 minmtu 68 maxmtu 0
erspan remote any local any ttl inherit nopmtudisc okey 0.0.0.0 erspan_index 0 erspan_ver 1 addrgenmode eui64 numtxqueues 1 numrxqueues 1 gso_max_size 65536 gso_max_segs 65535
7: net1@erspan0: <BROADCAST,MULTICAST,UP,LOWER_UP,M-DOWN> mtu 1500 qdisc noqueue state UNKNOWN mode DEFAULT group default