请问这道题的开销是20还是30？

789qw789

请问这道题的开销是20还是30？

如图所示IS-IS网络中， RTA、 RTB、RTC配置如下：

RTA]isis

RTA-isis-1]is-level level-1

RTA-isis-1]network-entit01.1111.1111.1111.00

RTA-isis-1]interface serial 2/0

RTA-Serial2/0]isis enable 1

RTB]isis

RTB-isis-1]is-level level-1

RTB-isis-1]network-entit01.2222.2222.2222.00

RTB-isis-1]interface serial 1/0

RTB-Serial1/0]isis enable 1

RTB-Serial1/0]interface Ethernet 0/0

RTB-Ethernet0/0]isis enable 1

RTC]isis

RTC-isis-1]is-level level-1

RTC-isis-1]network-entit01.3333.3333.3333.00

RTC-isis-1]interface Ethernet 0/0

RTC-Ethernet0/0]isis enable 1

RTC-Ethernet0/0]interface Ethernet 0/1

RTC-Ethernet0/1]isis enable 1

各路由器路由稳定后，RTA 上IS-IS路由 192.168.3.0/24的开销是 ______。

A. 3

B. 2

C. 1563

D. 30

E. 20