I wanted to quickly attack a few points tonight as I am mentally dead between working and studying simultaneously.

One thing I found amazingly interesting when familiarizing myself with debug output for “debug eigrp packets” especially with passive interfaces, is that the loopback interface is creating as much if not unneeded output than the Fa0/0 interface I am trying to prove is wasting CPU:

R2#debug eigrp pack
EIGRP Packets debugging is on
(UPDATE, REQUEST, QUERY, REPLY, HELLO, IPXSAP, PROBE, ACK, STUB, SIAQUERY, SIAREPLY)
R2#
*Mar  1 09:57:49.767: EIGRP: Sending HELLO on Serial0/0
*Mar  1 09:57:49.767:   AS 100, Flags 0x0, Seq 0/0 idbQ 0/0 iidbQ un/rely 0/0
*Mar  1 09:57:49.972: EIGRP: Sending HELLO on FastEthernet0/0
*Mar  1 09:57:49.972:   AS 100, Flags 0x0, Seq 0/0 idbQ 0/0 iidbQ un/rely 0/0
*Mar  1 09:57:50.120: EIGRP: Sending HELLO on Loopback2
*Mar  1 09:57:50.120:   AS 100, Flags 0x0, Seq 0/0 idbQ 0/0 iidbQ un/rely 0/0
*Mar  1 09:57:50.120: EIGRP: Received HELLO on Loopback2 nbr 2.2.2.2
*Mar  1 09:57:50.124:   AS 100, Flags 0x0, Seq 0/0 idbQ 0/0
*Mar  1 09:57:50.124: EIGRP: Packet from ourselves ignored
R2#
*Mar  1 09:57:51.991: EIGRP: Received HELLO on FastEthernet0/0 nbr 172.12.23.3
*Mar  1 09:57:51.995:   AS 100, Flags 0x0, Seq 0/0 idbQ 0/0 iidbQ un/rely 0/0 peerQ un/rely 0/0
*Mar  1 09:57:54.439: EIGRP: Sending HELLO on FastEthernet0/0
*Mar  1 09:57:54.439:   AS 100, Flags 0x0, Seq 0/0 idbQ 0/0 iidbQ un/rely 0/0
*Mar  1 09:57:54.956: EIGRP: Sending HELLO on Loopback2
*Mar  1 09:57:54.956:   AS 100, Flags 0x0, Seq 0/0 idbQ 0/0 iidbQ un/rely 0/0
*Mar  1 09:57:54.956: EIGRP: Received HELLO on Loopback2 nbr 2.2.2.2
*Mar  1 09:57:54.960:   AS 100, Flags 0x0, Seq 0/0 idbQ 0/0
*Mar  1 09:57:54.960: EIGRP: Packet from ourselves ignored

THOSE LOOPBACK ADDRESSES ARE SENDING AND RECEIVING UNNECESSARY TRAFFIC EVERY 5 SECONDS, THAT IS A CPU CRIME, AND I WILL NOT STAND FOR IT!

The idea is, you want interfaces that don’t have EIGRP speaking routers sending EIGRP traffic, as it wastes CPU resources. I ran “debug eigrp pack” like I did in my training video, but on my equipment it showed that not only the Fa0/0 LAN portion that doesn’t need traffic on it is sending Hello’s every 5 seconds, but SO ARE THE LOOPBACK INTERFACES – And they even have an Ignore-Self-Traffic message at the end which makes you wonder WHY WOULD YOU EVEN SEND IT TO YOURSELF IN THE FIRST PLACE?!?

However, the above output shows the one humble Hello from the Serial Interface, than Loopback and FastEthernet traffic every 5 seconds on the dot, though I didn’t post the full output as fun as it is to read (but did color code the snapshot of output to make it clear the atrocity Loopback2 is committing). So I got into router config, passive-interface both fa0/0 and lo2 / lo3 on my spoke routers and life is good.

Summary routes cannot get a whole lot more straight forward, you do have to remember to enter all the different networks into EIGRP via the network command, and then the single statement on the interface to advertise the networks from. In my case I made loopbacks for networks 100.1.0.0 – 100.7.0.0 /24, which summarization math turns to 100.0.0.0 /13, then on interface S0/0 entered:

R1(config-if)#ip summary-address eigrp 100 100.0.0.0 255.248.0.0
R1(config-if)#
*Mar  1 12:12:03.411: %DUAL-5-NBRCHANGE: IP-EIGRP(0) 100: Neighbor 172.12.123.3 (Serial0/0) is resync: summary configured
*Mar  1 12:12:03.411: %DUAL-5-NBRCHANGE: IP-EIGRP(0) 100: Neighbor 172.12.123.2 (Serial0/0) is resync: summary configured
R1(config-if)#

However I did learn after going to R2 and doing ‘sh ip route’ that it will not show the summary route without the networks being entered into EIGRP configuration. Also to note of course to see it’s Summary address of 5 you must be on the router with the summary address configured, and type in “show ip route 100 100.0.0.0 255.248.0.0” or in the “show run” it will show the number 5 after the summary address in the configuration.

The following will be some pretty boring output to most, but this is going to be me making the two spokes R2 and R3 stub routers in this EIGRP network, and I’m just going to throw the chunks of info up and go through the output after it, and its for both routers so it should be a large chunk of output:

R3(config-router)#eigrp stub
R3(config-router)#
*Mar  1 13:36:58.257: %DUAL-5-NBRCHANGE: IP-EIGRP(0) 100: Neighbor 172.12.123.1 (Serial0/2) is down: peer info changed
R3(config-router)#
R3(config-router)#do sh ip route
(Route codes redacted)

Gateway of last resort is not set

3.0.0.0/32 is subnetted, 1 subnets
C       3.3.3.3 is directly connected, Loopback3
172.12.0.0/24 is subnetted, 2 subnets
C       172.12.23.0 is directly connected, FastEthernet0/0
C       172.12.123.0 is directly connected, Serial0/2
R3(config-router)#
*Mar  1 13:37:07.364: %DUAL-5-NBRCHANGE: IP-EIGRP(0) 100: Neighbor 172.12.123.1 (Serial0/2) is up: new adjacency
R3(config-router)#do sh ip route
(Route codes redacted)

Gateway of last resort is not set

1.0.0.0/32 is subnetted, 1 subnets
D       1.1.1.1 [90/2297856] via 172.12.123.1, 00:00:08, Serial0/2
2.0.0.0/32 is subnetted, 1 subnets
D       2.2.2.2 [90/2809856] via 172.12.123.1, 00:00:08, Serial0/2
100.0.0.0/13 is subnetted, 1 subnets
D       100.0.0.0 [90/2297856] via 172.12.123.1, 00:00:08, Serial0/2
3.0.0.0/32 is subnetted, 1 subnets
C       3.3.3.3 is directly connected, Loopback3
172.12.0.0/24 is subnetted, 2 subnets
C       172.12.23.0 is directly connected, FastEthernet0/0
C       172.12.123.0 is directly connected, Serial0/2
R3(config-router)#

So it took a hit on its neighbor relationships by about 10 seconds given the timestamps on the output, and it still has all EIGRP routes it should, let us see R1’s ‘sh ip route’ output:

R1#sh ip route
(Route codes redacted)

Gateway of last resort is not set

1.0.0.0/32 is subnetted, 1 subnets
C       1.1.1.1 is directly connected, Loopback1
2.0.0.0/32 is subnetted, 1 subnets
D       2.2.2.2 [90/2297856] via 172.12.123.2, 00:35:53, Serial0/0
100.0.0.0/8 is variably subnetted, 8 subnets, 2 masks
C       100.4.0.0/16 is directly connected, Loopback104
C       100.5.0.0/16 is directly connected, Loopback105
C       100.6.0.0/16 is directly connected, Loopback106
C       100.7.0.0/16 is directly connected, Loopback107
D       100.0.0.0/13 is a summary, 00:34:06, Null0
C       100.1.0.0/16 is directly connected, Loopback101
C       100.2.0.0/16 is directly connected, Loopback102
C       100.3.0.0/16 is directly connected, Loopback103
3.0.0.0/32 is subnetted, 1 subnets
D       3.3.3.3 [90/2297856] via 172.12.123.3, 00:05:02, Serial0/0
172.12.0.0/24 is subnetted, 2 subnets
D       172.12.23.0 [90/2172416] via 172.12.123.3, 00:05:02, Serial0/0
[90/2172416] via 172.12.123.2, 00:05:02, Serial0/0
C       172.12.123.0 is directly connected, Serial0/0
R1#

Both Loopbacks and the LAN network are still there, it is unaffected by the Stub command on R2 which it should be. However it is taught that two stubs on the same network cannot form an EIGRP adjacency, so I am looking forward to what sort of mess that will cause making that a stub next. Here is the change output from R3:

R3(config-router)#eigrp stub
R3(config-router)#^Z
R3#
*Mar  1 13:47:03.966: %SYS-5-CONFIG_I: Configured from console by console
R3#show ip route
(Route codes redacted)

Gateway of last resort is not set

1.0.0.0/32 is subnetted, 1 subnets
D       1.1.1.1 [90/2297856] via 172.12.123.1, 00:10:02, Serial0/2
2.0.0.0/32 is subnetted, 1 subnets
D       2.2.2.2 [90/2809856] via 172.12.123.1, 00:10:02, Serial0/2
100.0.0.0/13 is subnetted, 1 subnets
D       100.0.0.0 [90/2297856] via 172.12.123.1, 00:10:02, Serial0/2
3.0.0.0/32 is subnetted, 1 subnets
C       3.3.3.3 is directly connected, Loopback3
172.12.0.0/24 is subnetted, 2 subnets
C       172.12.23.0 is directly connected, FastEthernet0/0
C       172.12.123.0 is directly connected, Serial0/2

I was fully expecting to lose a route or see some DUAL DON’T PLAY THAT HOMIE console messages, but I got nothing when making that stub change, all routes are as they should be. Then I started to think of the wording, an adjacency is a neighbor relationship:

R3#show ip eigrp nei
IP-EIGRP neighbors for process 100
H   Address                 Interface       Hold Uptime   SRTT   RTO  Q  Seq
(sec)         (ms)       Cnt Num
0   172.12.123.1            Se0/2            154 00:11:31   58   348  0  19

So to test if that is correct I will take off stub routing quick, I jumped on both spoke routers, and removed the stub routing command from EIGRP but they still only showed R1 as their only EIGRP neighbor, so I decided to turn off passive-interface to see if it’s something with the NBMA network and if the LAN would allow the neighborship to form:

R2#conf t
Enter configuration commands, one per line.  End with CNTL/Z.
R2(config)#router eigrp 100
R2(config-router)#no passive-interface fa0/0
R2(config-router)#
ASR#3
[Resuming connection 3 to r3 … ]

*Mar  1 13:52:48.543: %DUAL-5-NBRCHANGE: IP-EIGRP(0) 100: Neighbor 172.12.123.1 (Serial0/2) is up: new adjacency
R3(config-router)#no passive-interface fa0/0
R3(config-router)#
*Mar  1 13:56:39.530: %DUAL-5-NBRCHANGE: IP-EIGRP(0) 100: Neighbor 172.12.23.2 (FastEthernet0/0) is up: new adjacency
R3(config-router)#^Z
R3#
*Mar  1 13:56:46.745: %SYS-5-CONFIG_I: Configured from console by console
R3#sh ip eigrp nei
IP-EIGRP neighbors for process 100
H   Address                 Interface       Hold Uptime   SRTT   RTO  Q  Seq
(sec)         (ms)       Cnt Num
1   172.12.23.2             Fa0/0             14 00:00:19   10   200  0  22
0   172.12.123.1            Se0/2            160 00:04:10   50   300  0  26
R3#

And immediately we are all neighbors again, so that proved it was something to do with the Hub and Spoke / NBMA nature of the network. So I will leave those passive, so my spokes can have more than one neighbor to say Hello to, though those Loopbacks shall stay suppressed.

I still need to try getting ip default-network to propagate to my spoke routers, but I am officially 100% fried on networking for today, I’ll have a micro-segment regarding that if I get to it before some OSPF re-labbing 🙂