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

QUESTION 222
What’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
B. it check the egress access list
4 k1 P$ J* X9 B, ~' m4 y. t# \C. Route available in FIB ot it verifies a reverse patch via the fib to the source
D. it verify that the source has a......
% _8 h$ @- U9 L1 b8 F: ECorrect Answer: C

: b8 f/ X0 n6 @- q; `9 Y7 S! wQUESTION 202
When unicast reverse path forwarding is configured on an interface, which action does the interface take first when it receives a packet?
8 X9 L8 {- L. }. B! ?  \/ X) s) WA. It check the ingress access list
B. It check the egress access list
$ ~+ o- X/ x3 s! Q6 d& w# x* \3 mC. It verifies that the source has a valid CEF adjacency
, L' Q& |/ T: D8 i4 i. }4 HD. It verifies a reverse path via the FIB to the source
Correct Answer: A

QUESTION 223
  Y0 A) u' m. ?8 U8 w4 L' Z; ?Two scenarios for preventing fragmentation on GRE tunnel(Choose two)
A. TCP MSS
; f; B/ L& X) y# XB. DF Bit Clear
C. IP MTU
0 G0 i2 y8 |+ z! y( J, QD. PMTUD
9 U# J0 p  J2 q$ G. {! V$ YE. http://bbs.hh010.com/
; q; r$ {9 Z. Z9 d  {, v; y" iF. http://bbs.hh010.com/
Correct Answer: AD

QUESTION 220
% M7 N2 }! n- p7 J0 p2 kTwo GRE sccenarios for preventing(Choose two)
+ {! X( L# A: `& h/ K9 JA. TCP MSS
, o3 ?1 ]5 h5 b9 |, P  h6 DB. DF Bit
4 \) D3 C1 O; L& IC. http://bbs.hh010.com/
D. http://bbs.hh010.com/
Correct Answer: AB

joward

joward

求答案

liugangpaul

2 X# r9 e4 N0 C& b& I/ m1 F
* x4 p, F* \0 W  z( [) c5 ^QUESTION 202和222问的其实是一样的内容
参考CCNP学习指南英文版（300新版）关于uRPF的叙述：
Network administrators can use Unicast Reverse Path Forwarding (uRPF) to help limit
, L" {' _  W- ], x# Fthe malicious traffic on an enterprise network. This security feature works with Cisco
9 H# T/ A: L# P8 h, Y4 y7 CExpress Forwarding (CEF) by enabling the router to verify that the source of any IP
packets received is in the CEF table and reachable via the routing table. If the source IP
address is not valid, the packet is discarded.

access list与ACL有关，可以排除
CEF和FIB，我倾向于选FIB，符合上述中的reachable via the routing table

' `* Y. L, a) c' |- N
: S5 `1 u5 o1 V1 Z& Y
请各位指教
( ?$ l+ g- c; j: B

liugangpaul

220和223看起来也像同一道题，我选TCP MSS和PMTUD

1 N) A! `0 K% d4 Q/ L参见http://www.cisco.com/c/en/us/sup ... 5-pmtud-ipfrag.html

maomaoqd

请教有正确答案了吗?