4月10日路由题库的几道题

joward

求高手指导，QUESTION 222和QUESTION 202、QUESTION 223和QUESTION 220，好像答案有点问题

/ Q* U$ H, G! Y) e0 H, ~- U6 Q& HQUESTION 222
6 c! h5 A* i- D" WWhat’s uRPF checking first when the packet enters the interface ? or when unicast reverse patch forwarding is configured on interinterface.
A. it check the ingress access list
0 J+ f! P3 y7 Q9 a$ FB. it check the egress access list
C. Route available in FIB ot it verifies a reverse patch via the fib to the source
. l# V; A" P$ [+ ~D. it verify that the source has a......
Correct Answer: C
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) I/ E4 |# c" pQUESTION 202
( R0 f0 p: G) S% rWhen unicast reverse path forwarding is configured on an interface, which action does the interface take first when it receives a packet?
A. It check the ingress access list
B. It check the egress access list
C. It verifies that the source has a valid CEF adjacency
D. It verifies a reverse path via the FIB to the source
Correct Answer: A

7 m6 I4 W" @% J$ _9 nQUESTION 223
& g( g* l5 S5 `$ I* [5 vTwo scenarios for preventing fragmentation on GRE tunnel(Choose two)
A. TCP MSS
B. DF Bit Clear
C. IP MTU
D. PMTUD
E. http://bbs.hh010.com/
F. http://bbs.hh010.com/
' j5 }- U. ^5 T  e  _4 v+ D1 r' @# _Correct Answer: AD
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  Q3 r, p! F" T) ]1 ~QUESTION 220
Two GRE sccenarios for preventing(Choose two)
A. TCP MSS
- j; e2 A; i& u) I" Z; YB. DF Bit
C. http://bbs.hh010.com/
% J. O' b& p6 M/ i  uD. http://bbs.hh010.com/
* ^1 k$ _( o. k# O) MCorrect Answer: AB
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joward

joward

求答案

liugangpaul

& ], `) x7 s$ E+ W- ^5 D0 D3 M
QUESTION 202和222问的其实是一样的内容
2 U* ^; l6 F5 y  g参考CCNP学习指南英文版（300新版）关于uRPF的叙述：
: q% {* c; M5 j3 XNetwork administrators can use Unicast Reverse Path Forwarding (uRPF) to help limit
$ Z# F3 e1 z0 w$ V, tthe malicious traffic on an enterprise network. This security feature works with Cisco
Express Forwarding (CEF) by enabling the router to verify that the source of any IP
; M; H. l( ~7 B: Z/ ?  s# E7 cpackets received is in the CEF table and reachable via the routing table. If the source IP
8 E  L- Y# @( ?# a1 P, ^address is not valid, the packet is discarded.
7 k7 M' `3 b& y
7 r3 {( c1 ^1 o) m2 Aaccess list与ACL有关，可以排除
' W4 V7 B& M8 ^! o& s7 ]; f) DCEF和FIB，我倾向于选FIB，符合上述中的reachable via the routing table
4 H3 s+ E: l4 h: A
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请各位指教
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liugangpaul

220和223看起来也像同一道题，我选TCP MSS和PMTUD
& W4 I. R! {2 V
参见http://www.cisco.com/c/en/us/sup ... 5-pmtud-ipfrag.html

maomaoqd

请教有正确答案了吗?