CCIE-R&S笔试题疑问？求大神解答

wukunpeng

Which two options are causes of out-of-order packets? (Choose two.)
A. a routing loop
B. a router in the packet flow path that is intermittently dropping packets
C. high latency
D. packets in a flow traversing multiple paths through the network
E. some packets in a flow being process-switched and others being interrupt-switched on a transit router
Correct Answer: DE

这道题为什么选E啊    选DE我可以理解，毕竟如果在cisco上关闭cef的话是可以两条路由都进行转发负载的，有可能导致收到的数据包无序；为什么C是错误的解释呢  C为高延迟，如果链路延迟比较高的话也有可能先收到3号包再收到1号包吧，E是说一些包在流经转发路由器时 有的进行了正常转发/队列转发、有的进行了转发中断/中断转发  这个也有可能，不管是UDP还是TCP   TCP进行重传的话包自然无序UDP不管是否重传中断传输部分的包肯定也是无序的，但是为什么C是错误的呢

zjie

延迟不管大小，在一条链路上，其数据包的传输都是顺序的，如果因为某设备负载性能问题，延迟加大，并不影响数据包的传输顺序

zjie

倒是interrupt-switched不是太理解，它跟process-switched如何区分，都要走cpu的呀，是不是interrupt-switched优先？

zjie

了解了，原来interrupt switching就指的是fast switching， optimum switching，cef

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tobe钢铁侠

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zhaochunhui

zjie 发表于 2014-8-15 10:11
了解了，原来interrupt switching就指的是fast switching， optimum switching，cef

Also, if some packets are process switched quickly by the routing engine of the router while others
are interrupt switched (which takes more time) then it could result in out of order packets. 从解释上看。应该是 process switched 转发速度比 interrupt switched要更快。所以导致收到无序包

你好啊123

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