Ticket #06

Ticket #06

Network diagram

IGP diagram


The problem:

R2 can't ping both R1's Lo11 and R4's Lo44 at the same time from all its interface. Fix the problem.

The solution:

First lets try to ping to to these addresses from R2. Notice: You might see some different results, the reason for that is explained later on.

On R2:

R2#ping 10.1.1.1

Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 10.1.1.1, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 1/9/24 ms
R2#ping 10.4.4.4

Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 10.4.4.4, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 4/10/16 ms
R2#ping 10.1.1.1 so lo 0

Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 10.1.1.1, timeout is 2 seconds:
Packet sent with a source address of 5.11.2.2
U.U.U
Success rate is 0 percent (0/5)
R2#ping 10.4.4.4 so lo 0

Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 10.4.4.4, timeout is 2 seconds:
Packet sent with a source address of 5.11.2.2
U.U.U
Success rate is 0 percent (0/5)

We can see that we where not able to ping to R4's Lo44 nad R1's Lo11 IP addresses from all R2's interfaces. Could it be that R1 and R4 do not have a route back to all R2's interfaces?

On R1:

R1#sh ip route 5.11.23.2
Routing entry for 5.11.23.0/24
  Known via "eigrp 11", distance 90, metric 30720, type internal
  Redistributing via eigrp 11
  Last update from 5.11.13.3 on FastEthernet0/0, 00:39:15 ago
  Routing Descriptor Blocks:
  * 5.11.13.3, from 5.11.13.3, 00:39:15 ago, via FastEthernet0/0
      Route metric is 30720, traffic share count is 1
      Total delay is 200 microseconds, minimum bandwidth is 100000 Kbit
      Reliability 255/255, minimum MTU 1500 bytes
      Loading 1/255, Hops 1

R1#sh ip route 5.11.2.2
Routing entry for 5.11.2.2/32
  Known via "eigrp 11", distance 90, metric 158720, type internal
  Redistributing via eigrp 11
  Last update from 5.11.13.3 on FastEthernet0/0, 00:39:18 ago
  Routing Descriptor Blocks:
  * 5.11.13.3, from 5.11.13.3, 00:39:18 ago, via FastEthernet0/0
      Route metric is 158720, traffic share count is 1
      Total delay is 5200 microseconds, minimum bandwidth is 100000 Kbit
      Reliability 255/255, minimum MTU 1500 bytes
      Loading 1/255, Hops 2

On R4:

R4#sh ip route 5.11.23.2
Routing entry for 5.11.23.0/24
  Known via "eigrp 11", distance 90, metric 30720, type internal
  Redistributing via eigrp 11
  Last update from 5.11.34.3 on FastEthernet0/0, 00:39:59 ago
  Routing Descriptor Blocks:
  * 5.11.34.3, from 5.11.34.3, 00:39:59 ago, via FastEthernet0/0
      Route metric is 30720, traffic share count is 1
      Total delay is 200 microseconds, minimum bandwidth is 100000 Kbit
      Reliability 255/255, minimum MTU 1500 bytes
      Loading 1/255, Hops 1

R4#sh ip route 5.11.2.2
Routing entry for 5.11.2.2/32
  Known via "eigrp 11", distance 90, metric 158720, type internal
  Redistributing via eigrp 11
  Last update from 5.11.34.3 on FastEthernet0/0, 00:40:02 ago
  Routing Descriptor Blocks:
  * 5.11.34.3, from 5.11.34.3, 00:40:02 ago, via FastEthernet0/0
      Route metric is 158720, traffic share count is 1
      Total delay is 5200 microseconds, minimum bandwidth is 100000 Kbit
      Reliability 255/255, minimum MTU 1500 bytes
      Loading 1/255, Hops 2

Both routers got the correct route back to R2's interfaces, pointing to R3.


Lets check the routing on R3 for both R2's interfaces and for R4's Lo44 IP address and R1's Lo11 IP address.

On R3:

R3#sh ip route 5.11.23.2
Routing entry for 5.11.23.0/24
  Known via "connected", distance 0, metric 0 (connected, via interface)
  Redistributing via eigrp 11
  Routing Descriptor Blocks:
  * directly connected, via FastEthernet0/0.23
      Route metric is 0, traffic share count is 1

R3#sh ip route 5.11.2.2
Routing entry for 5.11.2.2/32
  Known via "eigrp 11", distance 90, metric 156160, type internal
  Redistributing via eigrp 11
  Last update from 5.11.23.2 on FastEthernet0/0.23, 00:41:25 ago
  Routing Descriptor Blocks:
  * 5.11.23.2, from 5.11.23.2, 00:41:25 ago, via FastEthernet0/0.23
      Route metric is 156160, traffic share count is 1
      Total delay is 5100 microseconds, minimum bandwidth is 100000 Kbit
      Reliability 255/255, minimum MTU 1500 bytes
      Loading 1/255, Hops 1

R3#sh ip route 10.1.1.1
Routing entry for 10.0.0.0/8
  Known via "eigrp 11", distance 90, metric 156160, type internal
  Redistributing via eigrp 11
  Last update from 5.11.34.4 on FastEthernet0/0.34, 00:41:30 ago
  Routing Descriptor Blocks:
    5.11.34.4, from 5.11.34.4, 00:41:30 ago, via FastEthernet0/0.34
      Route metric is 156160, traffic share count is 1
      Total delay is 5100 microseconds, minimum bandwidth is 100000 Kbit
      Reliability 255/255, minimum MTU 1500 bytes
      Loading 1/255, Hops 1
  * 5.11.13.1, from 5.11.13.1, 00:41:30 ago, via FastEthernet0/0.13
      Route metric is 156160, traffic share count is 1
      Total delay is 5100 microseconds, minimum bandwidth is 100000 Kbit
      Reliability 255/255, minimum MTU 1500 bytes
      Loading 1/255, Hops 1


R3#sh ip route 10.4.4.4
Routing entry for 10.0.0.0/8
  Known via "eigrp 11", distance 90, metric 156160, type internal
  Redistributing via eigrp 11
  Last update from 5.11.34.4 on FastEthernet0/0.34, 00:42:02 ago
  Routing Descriptor Blocks:
    5.11.34.4, from 5.11.34.4, 00:42:02 ago, via FastEthernet0/0.34
      Route metric is 156160, traffic share count is 1
      Total delay is 5100 microseconds, minimum bandwidth is 100000 Kbit
      Reliability 255/255, minimum MTU 1500 bytes
      Loading 1/255, Hops 1
  * 5.11.13.1, from 5.11.13.1, 00:42:02 ago, via FastEthernet0/0.13
      Route metric is 156160, traffic share count is 1
      Total delay is 5100 microseconds, minimum bandwidth is 100000 Kbit
      Reliability 255/255, minimum MTU 1500 bytes
      Loading 1/255, Hops 1

We can see that R3 have the correct routes to R2's interfaces IP addresses, but it got a strange routing information for R4's Lo44 and R2's Lo11 IP address.

For both Looback interfaces, R3 sees a 10.0.0.0/8 instead of a specific route, and both R4 and R1 advertise a 10.0.0.0/8 route instead of a /32 route for their Loopback interface.

Maybe a summary route is configured on R1's and R4's FastEthernet0/0 interface?

On R1:

R1#sh run int f0/0
Building configuration...

Current configuration : 94 bytes
!
interface FastEthernet0/0
 ip address 5.11.13.1 255.255.255.0
 duplex auto
 speed auto
end

There are no EIGRP configurations on R1's interface facing R3. Lets check all R1's EIGRP configurations.

On R1:

R1#sh run | sec router ei
router eigrp 11
 network 5.0.0.0
 network 10.0.0.0
 auto-summary

We can see the the problem! R1 is doing auto summary. Let check if we have the same problem on R4.

On R4:

R4#sh run | sec router ei
router eigrp 11
 network 5.0.0.0
 network 10.0.0.0
 auto-summary

We can see the same problem on R4.

Auto summary was left to its default enabled behavior. Thats why we see a /8 route for R4's Lo44 IP address and for R1's Lo11 IP address, instead of a /32 route.

Before fixing the problem, we need to explain to ourselves why R2 could ping to the loopbacks IP addresses from its FastEthernet0/0 interface but couldn't do so from its Lo0 IP address.

On R3:

R3#sh ip cef exact-route 5.11.23.2 10.1.1.1
5.11.23.2 -> 10.1.1.1 => IP adj out of FastEthernet0/0.13, addr 5.11.13.1
R3#sh ip cef exact-route 5.11.23.2 10.4.4.4
5.11.23.2 -> 10.4.4.4 => IP adj out of FastEthernet0/0.34, addr 5.11.34.4
R3#sh ip cef exact-route 5.11.2.2 10.1.1.1
5.11.2.2 -> 10.1.1.1 => IP adj out of FastEthernet0/0.34, addr 5.11.34.4
R3#sh ip cef exact-route 5.11.2.2 10.4.4.4
5.11.2.2 -> 10.4.4.4 => IP adj out of FastEthernet0/0.13, addr 5.11.13.1

We can see that for traffic sourced by R2's FastEthernet0/0 interface, R3's CEF selected the correct route, while for packets source from R2's Lo0, R3's CEF selected the wrong paths. How does R3 select the paths when it got multi path routes? Its not published! We can just see the current state.

The path selecting depends on the HW and on the SW, so CEF decisions migh be different on your lab.

Lets disable auto summary on both R1 and R4, and check R3's routing table again.

On R1:

R1(config)#router ei 11
R1(config-router)#no auto-summary
R1(config-router)#
*Dec 25 21:38:42.039: %DUAL-5-NBRCHANGE: IP-EIGRP(0) 11: Neighbor 5.11.13.3 (FastEthernet0/0) is resync: summary configured

On R4:

R4(config)#router ei 11
R4(config-router)#no auto-summary
R4(config-router)#
*Dec 25 21:38:42.039: %DUAL-5-NBRCHANGE: IP-EIGRP(0) 11: Neighbor 5.11.34.3 (FastEthernet0/0) is resync: summary configured

Now lets have a look at R3's routing table entry for R4's Lo44 and R1's Lo11 IP addresses.

On R3:

R3#sh ip route 10.1.1.1
Routing entry for 10.1.1.1/32
  Known via "eigrp 11", distance 90, metric 156160, type internal
  Redistributing via eigrp 11
  Last update from 5.11.13.1 on FastEthernet0/0.13, 00:01:15 ago
  Routing Descriptor Blocks:
  * 5.11.13.1, from 5.11.13.1, 00:01:15 ago, via FastEthernet0/0.13
      Route metric is 156160, traffic share count is 1
      Total delay is 5100 microseconds, minimum bandwidth is 100000 Kbit
      Reliability 255/255, minimum MTU 1500 bytes
      Loading 1/255, Hops 1

R3#sh ip route 10.4.4.4
Routing entry for 10.4.4.4/32
  Known via "eigrp 11", distance 90, metric 156160, type internal
  Redistributing via eigrp 11
  Last update from 5.11.34.4 on FastEthernet0/0.34, 00:01:09 ago
  Routing Descriptor Blocks:
  * 5.11.34.4, from 5.11.34.4, 00:01:09 ago, via FastEthernet0/0.34
      Route metric is 156160, traffic share count is 1
      Total delay is 5100 microseconds, minimum bandwidth is 100000 Kbit
      Reliability 255/255, minimum MTU 1500 bytes
      Loading 1/255, Hops 1

Now R3 got a /32 routes for R4's Lo44 and R1's Lo11 IP address and the routes are pointing to the correct outgoing interfaces.

Lets try again to ping from R2 to these Loopback IP addresses.

On R2

R2#ping 10.1.1.1        

Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 10.1.1.1, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 4/9/16 ms
R2#ping 10.4.4.4        

Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 10.4.4.4, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 8/10/16 ms
R2#ping 10.1.1.1 so lo 0

Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 10.1.1.1, timeout is 2 seconds:
Packet sent with a source address of 5.11.2.2
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 8/8/8 ms
R2#ping 10.4.4.4 so lo 0

Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 10.4.4.4, timeout is 2 seconds:
Packet sent with a source address of 5.11.2.2
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 4/7/8 ms

Success!
                                          __ 
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