! First, the current successor route on R4 points out S0/0.1, to R1, metric 2048. 

R4# sh ip route
! lines omitted for brevity 
     172.31.0.0/16 is variably subnetted, 9 subnets, 2 masks 
D       172.31.211.0/24 [90/2048] via 172.31.14.1, 00:01:46, Serial0/0.1 

! Below, the FD is listed as 2048 as well. The topology entry for the successor 
! has the same 2048 metric listed as the first number in parentheses; the second 
! number is the RD on R1 (1280). The second topology entry for this route lists 
! metric 2560, RD 1792; with RD in the second route being less than the FD, this 
! second route meets the feasibility condition, making it an FS route. 

R4# show ip eigrp toplogy 
IP-EIGRP Topology Table for AS(1)/ID(172.31.104.4) 
Codes: P - Passive, A - Active, U - Update, Q - Query, R - Reply, 
r - reply Status, s - sia Status 
! lines omitted for brevity 
P 172.31.211.0/24, 1 successors, FD is 2048 
        via 172.31.14.1 (2048/1280), Serial0/0.1 
        via 172.31.24.2 (2560/1792), Serial0/0.2 

! Next, R4 loses Neighbor R1, with EIGRP Finite State Machine (FSM) debug on. 
R4# debig eigrp fsm
EIGRP FSM Events/Actions debugging is on 
Jan 12 07:17:42.391: %DUAL-5-NBRCHANGE: IP-EIGRP(0) 1: Neighbor 172.31.14.1 (Serial0/0.1) 
  is down: holding time expired 

! Below, debug messages have been edited to only show messages relating to 
! the route to 172.31.211.0/24. R4 looks for an FS, finds it, replaces the old 
! successor with the FS, and sends updates telling neighbors about the new route. 
Jan 12 07:17:42.399: DUAL: Destination 172.31.211.0/24 
Jan 12 07:17:42.399: DUAL: Find FS for dest 172.31.211.0/24. FD is 2048, RD is 2048 
Jan 12 07:17:42.399: DUAL: 172.31.14.1 metric 4294967295/4294967295 
Jan 12 07:17:42.399: DUAL: 172.31.24.2 metric 2560/1792 found Dmin is 2560 
Jan 12 07:17:42.399: DUAL: Removing dest 172.31.211.0/24, nexthop 172.31.14.1 
Jan 12 07:17:42.403: DUAL: RT installed 172.31.211.0/24 via 172.31.24.2 
Jan 12 07:17:42.403: DUAL: Send update about 172.31.211.0/24.  Reason: metric chg 
Jan 12 07:17:42.403: DUAL: Send update about 172.31.211.0/24.  Reason: new if
 
! Finally, note that the FD is unchanged; the FD is never raised until the route 
! has been actively queried. The new route info has been put in the routing table.
 
R4# show ip eigrp topology
! lines omitted for brevity 
P 172.31.211.0/24, 1 successors, FD is 2048 
        via 172.31.24.2 (2560/1792), Serial0/0.2 

R4# show ip route
! Lines omitted for brevity 
D       172.31.211.0/24 [90/2560] via 172.31.24.2, 00:00:25, Serial0/0.2 


=======================
=======================
=======================

! First, the show ip eigrp topology command only lists the successor route, and no 
! FS routes. This command does not list non-FS routes. <Edit by IPv6Freely: Poorly worded!!>
 
R4# show ip eigrp topology 
! Lines omitted for brevity 
P 172.31.151.0/24, 1 successors, FD is 1536 
        via 172.31.14.1 (1536/768), Serial0/0.1 

! Below, the show ip eigrp topology all-links command includes non-FS routes, 
! in this case including the non-FS route to 151.0/24 through R2. Note that this 
! alternate non-FS route’s RD is 1792, which is more than the FD of 1536. 

R4# show ip eigrp topology all-links
! Lines omitted for brevity 
P 172.31.151.0/24, 1 successors, FD is 1536, serno 175 
        via 172.31.14.1 (1536/768), Serial0/0.1 
        via 172.31.24.2 (2560/1792), Serial0/0.2
 
! Next, the FSM debug is again enabled, and R4 loses neighbor R1. 
R4# debug eigrp fsm
Jan 12 07:16:04.099: %DUAL-5-NBRCHANGE: IP-EIGRP(0) 1: Neighbor 172.31.14.1 (Serial0/0.1) 
  is down: holding time expired 
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! 
! Below, R4 looks for an FS for route 172.31.151.0/24, and does not find one— 
! so it enters active state. R4 sends a query to its one remaining neighbor (R2), 
! and keeps track of the number of outstanding Queries (1). Upon receiving the 
! Reply from R2, it can update its topology table, and repeat local computation, 
! and use the now-best route through R2. 
Jan 12 07:17:42.391: %DUAL-5-NBRCHANGE: IP-EIGRP(0) 1: Neighbor 172.31.14.1 (Serial0/0.1) 
  is down: holding time expired
Jan 12 07:17:42.391: DUAL: linkdown: start - 172.31.14.1 via Serial0/0.1 
Jan 12 07:17:42.391: DUAL: Destination 172.31.151.0/24 
Jan 12 07:17:42.391: DUAL: Find FS for dest 172.31.151.0/24. FD is 1536, RD is 1536 
Jan 12 07:17:42.395: DUAL:  172.31.14.1 metric 4294967295/4294967295 
Jan 12 07:17:42.395: DUAL:  172.31.24.2 metric 2560/1792 not found Dmin is 2560 
Jan 12 07:17:42.395: DUAL: Dest 172.31.151.0/24 entering active state. 
Jan 12 07:17:42.395: DUAL: Set reply-status table. Count is 1. 
Jan 12 07:17:42.395: DUAL: Not doing split horizon 
Jan 12 07:17:42.459: DUAL: rcvreply: 172.31.151.0/24 via 172.31.24.2 metric 2560/1792 
Jan 12 07:17:42.459: DUAL: reply count is 1 
Jan 12 07:17:42.459: DUAL: Clearing handle 0, count now 0 
Jan 12 07:17:42.463: DUAL: Freeing reply status table 
Jan 12 07:17:42.463: DUAL: Find FS for dest 172.31.151.0/24. FD is 4294967295, RD is 
  4294967295 found 
Jan 12 07:17:42.463: DUAL: Removing dest 172.31.151.0/24, nexthop 172.31.14.1 
Jan 12 07:17:42.463: DUAL: RT installed 172.31.151.0/24 via 172.31.24.2 
Jan 12 07:17:42.467: DUAL: Send update about 172.31.151.0/24.  Reason: metric chg 
Jan 12 07:17:42.467: DUAL: Send update about 172.31.151.0/24.  Reason: new if 
! Next, note that because R4 actively queried for the route, the FD could change. 
R4# show ip eigrp topology 
IP-EIGRP Topology Table for AS(1)/ID(172.31.104.4) 
Codes: P - Passive, A - Active, U - Update, Q - Query, R - Reply, 
       r - reply Status, s - sia Status 
P 172.31.151.0/24, 1 successors, FD is 2560 
via 172.31.24.2 (2560/1792), Serial0/0.2