Cisco CCNP BSCI 3.0(EIGRP Updates and Queries in Hub-and-Spoke Topology)
在Cisco CCNP BSCI 3.0的教材中(P.2-84)，有一篇描敘EIGRP Query & Update的scenario，第一次看到這張圖片(如附圖)的同學一定看得頭昏眼花，根本不知道課本中想要表達的來龍去脈，更不知道為何會發生Stuck-In-Active(SIA)，因此我回頭查了一下舊版的BSCI教材，原來是新版的內容將部份內容加以省略了，但是個人認為這實在是應該要說明清楚，避免學生囫圇吞棗不知所以然，因此我特別將舊版中省略的所有流程及細節一一列出，希望對各位學習有立竿見影之成效。
1. B == QUERY ==> C,D,E and A
2. C,D,E == REPLY(Next-Hop:A) ==> B
A == QUERY ==> C,D,E(Then C,D,E will remove the route 10.1.8.0/24 from routing table)
3. C,D,E == QUERY ==> B
(B is still waiting for A's reply)
(A is still waiting for C,D,E's reply)
(C,D,E are still waiting for B's reply)
=> Deadlock ...
4. B - A => Stuck-In-Active(SIA)(more than 3 minutes without reply from A)
5. B -X- A (Disconnect neighbor relationship)
B == REPLY(Next-Hop:NULL) ==> C,D,E
C,D,E == REPLY(Next-Hop:NULL) ==> A
6. A - B (Neighbor relationship re-establish)
A will remove 10.1.8.0/24 from routing table
1. B == QUERY ==> C,D,E and A
2. C,D,E == REPLY(Next-Hop:A) ==> B
A == QUERY ==> C,D,E(Then C,D,E will remove the route 10.1.8.0/24 from routing table)
3. C,D,E == QUERY ==> B
(B is still waiting for A's reply)
(A is still waiting for C,D,E's reply)
(C,D,E are still waiting for B's reply)
=> Deadlock ...
4. B - A => Stuck-In-Active(SIA)(more than 3 minutes without reply from A)
5. B -X- A (Disconnect neighbor relationship)
B == REPLY(Next-Hop:NULL) ==> C,D,E
C,D,E == REPLY(Next-Hop:NULL) ==> A
6. A - B (Neighbor relationship re-establish)
A will remove 10.1.8.0/24 from routing table
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