! 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