The next writing will be sample written content from your approaching CCIE R&S On-line Troubleshooting Bootcamp. Precisely what may cause an EIGRP membership in order to flap? According to Cisco, numerous motives. Listed here is a made clear checklist:
Actual hyperlink flaps.
Misconfigured howdy in addition to maintain time intervals. Your EIGRP maintain period of time is usually established independently from the howdy period of time if you issue the ip hold-time eigrp control. When you established a maintain period of time more compact compared to the howdy period of time, it brings about the friends flapping consistently. Cisco suggests that this maintain time become at the very least triple the howdy period of time. Should the importance is defined a lot less than thrice the howdy period of time, there exists the possibility for hyperlink flapping or neighborship flapping.
Decrease of Hi there packets: Hi there packets is usually dropped with extremely congested hyperlinks or error-prone hyperlinks (CRC mistakes, Figure mistakes, or extreme collisions).
Lifestyle of unidirectional hyperlinks.
Path moves stuck-in-active. When a router makes its way into the stuck-in-active express, the friends from which the response had been estimated tend to be reinitialized, plus the router moves productive with many tracks figured out from those people friends.
Supply of inadequate bandwidth for the EIGRP process. Whenever adequate bandwidth just isn't available, packets is usually dropped, which in turn causes friends to travel lower.
Poor serial wrinkles.
Wrongly established bandwidth phrases.
One-way multicast traffic.
Query hard thunder storms.
In this posting, allow us to verify the 2nd bullet position in excellent details with the control brand.
In this particular case, I've developed an effective EIGRP neighborship involving R4 in addition to R5 on the serial screen.
R5#show ip eigrp nei IP-EIGRP neighbors for process 100 H Address Interface Hold Uptime SRTT RTO Q Seq (sec) (ms) Cnt Num 0 10.10.10.4 Se0/0/0 10 00:00:18 5 200 0 3 R5#Let us examine the default hello and hold-time values for this circuit:
R5#show ip eigrp 100 interfaces detail s0/0/0 IP-EIGRP interfaces for process 100 Xmit Queue Mean Pacing Time Multicast Pending Interface Peers Un/Reliable SRTT Un/Reliable Flow Timer Routes Se0/0/0 1 0/0 5 0/15 50 0 Hello interval is 5 sec Next xmit serial Un/reliable mcasts: 0/0 Un/reliable ucasts: 0/3 Mcast exceptions: 0 CR packets: 0 ACKs suppressed: 2 Retransmissions sent: 0 Out-of-sequence rcvd: 0 Authentication mode is not set Use unicast R5#
As we can see the default hello interval is 5 seconds. We will trust Cisco in that the default hold-time is three times this interval. First of all, are differing timer values an issue on the two peers? Let us find out for sure:R5#conf t Enter configuration commands, one per line. End with CNTL/Z. R5(config)#int s0/0/0 R5(config-if)#ip hello-interval eigrp 100 30 R5(config-if)#ip hold-time eigrp 100 90 R5(config-if)#end R5# *Apr 19 18:50:20.251: %DUAL-5-NBRCHANGE: IP-EIGRP(0) 100: Neighbor 10.10.10.4 (Serial0/0/0) is down : Interface Goodbye received R5# *Apr 19 18:50:21.703: %SYS-5-CONFIG_I: Configured from console by console R5# *Apr 19 18:50:24.747: %DUAL-5-NBRCHANGE: IP-EIGRP(0) 100: Neighbor 10.10.10.4 (Serial0/0/0) is up: new adjacency R5#
Here we set the timers to 30 seconds and 90 seconds respectively. This tears down and reestablishes the adjacency, but it is indeed stable with no flapping. What are the timers that are in use now?R5#show ip eigrp 100 interfaces detail s0/0/0 IP-EIGRP interfaces for process 100 Xmit Queue Mean Pacing Time Multicast Pending Interface Peers Un/Reliable SRTT Un/Reliable Flow Timer Routes Se0/0/0 1 0/0 3 0/15 50 0 Hello interval is 30 sec Next xmit serial Un/reliable mcasts: 0/0 Un/reliable ucasts: 1/6 Mcast exceptions: 0 CR packets: 0 ACKs suppressed: 4 Retransmissions sent: 0 Out-of-sequence rcvd: 0 Authentication mode is not set Use unicast R5# Pod102ts1>4 [Resuming connection 4 to r4 ... ] * R4#show ip eigrp 100 interfaces detail s0/1/0 IP-EIGRP interfaces for process 100 Xmit Queue Mean Pacing Time Multicast Pending Interface Peers Un/Reliable SRTT Un/Reliable Flow Timer Routes Se0/1/0 1 0/0 5 0/15 50 0 Hello interval is 5 sec Next xmit serial Un/reliable mcasts: 0/0 Un/reliable ucasts: 2/6 Mcast exceptions: 0 CR packets: 0 ACKs suppressed: 3 Retransmissions sent: 0 Out-of-sequence rcvd: 0 Authentication mode is not set Use unicast R4#
Here we can see the hello intervals are set different with a stable neighborship. What is the actual interval in use? Let us check with debug eigrp packets:R4# *Apr 19 18:58:27.715: EIGRP: Received HELLO on Serial0/1/0 nbr 10.10.10.5 *Apr 19 18:58:27.715: AS 100, Flags 0x0, Seq 0/0 idbQ 0/0 iidbQ un/rely 0/0 peerQ un/rely 0/0 *Apr 19 18:58:27.731: EIGRP: Sending HELLO on Serial0/1/0 *Apr 19 18:58:27.731: AS 100, Flags 0x0, Seq 0/0 idbQ 0/0 iidbQ un/rely 0/0 R4# *Apr 19 18:58:32.703: EIGRP: Sending HELLO on Serial0/1/0 *Apr 19 18:58:32.703: AS 100, Flags 0x0, Seq 0/0 idbQ 0/0 iidbQ un/rely 0/0 R4# *Apr 19 18:58:37.111: EIGRP: Sending HELLO on Serial0/1/0 *Apr 19 18:58:37.111: AS 100, Flags 0x0, Seq 0/0 idbQ 0/0 iidbQ un/rely 0/0 R4# *Apr 19 18:58:41.451: EIGRP: Sending HELLO on Serial0/1/0 *Apr 19 18:58:41.451: AS 100, Flags 0x0, Seq 0/0 idbQ 0/0 iidbQ un/rely 0/0 R4# *Apr 19 18:58:46.319: EIGRP: Sending HELLO on Serial0/1/0 *Apr 19 18:58:46.319: AS 100, Flags 0x0, Seq 0/0 idbQ 0/0 iidbQ un/rely 0/0 R4# *Apr 19 18:58:51.059: EIGRP: Sending HELLO on Serial0/1/0 *Apr 19 18:58:51.059: AS 100, Flags 0x0, Seq 0/0 idbQ 0/0 iidbQ un/rely 0/0 R4# *Apr 19 18:58:55.891: EIGRP: Sending HELLO on Serial0/1/0 *Apr 19 18:58:55.891: AS 100, Flags 0x0, Seq 0/0 idbQ 0/0 iidbQ un/rely 0/0 R4# *Apr 19 18:58:57.619: EIGRP: Received HELLO on Serial0/1/0 nbr 10.10.10.5 *Apr 19 18:58:57.619: AS 100, Flags 0x0, Seq 0/0 idbQ 0/0 iidbQ un/rely 0/0 peerQ un/rely 0/0 R4#
Here we can see that R4 is sending Hello packets every 5 seconds, and it is receiving them from R5 every 30 seconds. Now to produce the flapping neighbor issue as Cisco describes:R5#conf t Enter configuration commands, one per line. End with CNTL/Z. R5(config)#int s0/0/0 R5(config-if)#no ip hello-interval eigrp 100 30 R5(config-if)#no ip hold-time eigrp 100 90 R5(config-if)#ip hello-interval eigrp 100 30 R5(config-if)#ip hold-time eigrp 100 15 R5(config-if)# Pod102ts1>4 [Resuming connection 4 to r4 ... ] * R4#conf t Enter configuration commands, one per line. End with CNTL/Z. R4(config)#int s0/1/0 R4(config-if)# R4(config-if)#ip hello-interval eigrp 100 30 R4(config-if)# R4(config-if)#ip hold-time eigrp 100 15 R4(config-if)#end R4# *Apr 19 19:07:13.067: %SYS-5-CONFIG_I: Configured from console by console *Apr 19 19:07:13.443: %DUAL-5-NBRCHANGE: IP-EIGRP(0) 100: Neighbor 10.10.10.5 (Serial0/1/0) is down : holding time expired R4# *Apr 19 19:07:25.603: %DUAL-5-NBRCHANGE: IP-EIGRP(0) 100: Neighbor 10.10.10.5 (Serial0/1/0) is up: new adjacency R4# *Apr 19 19:07:42.635: %DUAL-5-NBRCHANGE: IP-EIGRP(0) 100: Neighbor 10.10.10.5 (Serial0/1/0) is down : holding time expired R4# *Apr 19 19:07:54.451: %DUAL-5-NBRCHANGE: IP-EIGRP(0) 100: Neighbor 10.10.10.5 (Serial0/1/0) is up: new adjacency R4#
Here we see the flapping neighborship as a result of this misconfiguration of the timer values.
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