Summarization challenge

This exercise was first post by Arwin Reprakash (http://ithitman.blogspot.com/2015/03/configuring-ospf-summarization-lab.html#more). I took his post and modify it to create a new requirement

 

Startup configuration (VIRL)

Final configuration (VIRL)

THE PROBLEM

Summarize 192.168.1.2/32 from Area 2 as 192.168.1.0/24 into area 0. You have no Access to R1


RESTRICCIONS

* You only have Access to routers R2 and R3
* Do not use area-range command or summary-address to summarize the routes into Area 0.
* R3 and other routers in Area 0 or any new additional areas should only have the summary address to reach 192.168.1.2.
* If prefix 192.168.1.2/32 is withdrawn (i.e shutdown loopback0 on R2) from R1 OSPF database then 192.168.1.0/24 should not be summarized/advertised into area 0.


THE SOLUTION

When you run the lab you will notice that all the routers know how to reach each other by ospf. That's is good cause now we could créate a BGP relationship between R2 and R3 bypassing R1, and then advertise a summary address for R3

This is the configuration in R2 to summarize and advertise 192.168.1.0 (summary-only)

R2#show run | section bgp
router bgp 1
 bgp log-neighbor-changes
 network 192.168.1.2 mask 255.255.255.255
 aggregate-address 192.168.1.0 255.255.255.0 summary-only
 neighbor 13.13.13.3 remote-as 1

This is the configuration in R3

R3#show run | section bgp
router bgp 1
 bgp log-neighbor-changes
 neighbor 12.12.12.2 remote-as 1


Finally let's check the routing table in R3

R3#show ip route bgp
B     192.168.1.0/24 [200/0] via 12.12.12.2, 00:08:21


Ok it work,
When l0 in R2 is down, the route will  disappear from R3 routing table




I use cisco virl for these labs but i think they will work ok in GNS3 too.
Please leave your feedback

EIGRP Troubleshooting (summary-metric)

This exercise was first post by Arwin Reprakash (http://ithitman.blogspot.com/2015/01/eigrp-troubleshooting-lab-1.html#more). I took his post and found a way to resolve the problem

The diagrams and original idea belongs to Arwin Reprakash, please check the above link to see more details

 

 

Startup configuration file (VIRL)

 

 

THE PROBLEM

Everytime gi0/2 on R1 goes down, the metric to reach loopback 1 from R2 changes
The goal is to keep this metric the same

When gi0/2 in R1 is up

R2#sh ip route
 D 10.0.0.0 [90/3072] via 1.1.1.1, 00:03:59, GigabitEthernet1

When gi0/2 in R1 is down

R2#sh ip route
D 10.0.0.0 [90/130816] via 1.1.1.1, 00:00:05, GigabitEthernet1 


R1 advertises the route 10.0.0.0/23 as a summary address to R2, this summary addres groups R1 interfaces l0 and g0/2:

• l0/0 --> 10.0.0.1 255.255.255.0
• g0/2 --> 10.0.1.1 255.255.255.0

THE SOLUTION

For EIGRP, the smallest metric among the component routes (routes contained in the summary) will be employed as the summary route metric. That's why the metric changes when g0/2 is up or down

We need to find a way to fix the metric when the summary route is advertise. We can accomplish this with the command "summary-metric" inside the "router eigrp" process, but this command will ask us for the following values:

• Minimum bandwidth (Kbits)
• Total delay (tens of microseconds)
• Reliability
• Load
• Minimum MTU

To check which values is using the summary address (10.0.0.0/23) when gi0/2 i s up, we use the  command "show ip eigrp topology A.B.C.D":


#show ip eigrp topology 10.0.0.0 255.255.254.0

EIGRP-IPv4 Topology Entry for AS(100)/ID(10.0.0.1) for 10.0.0.0/23
  State is Passive, Query origin flag is 1, 1 Successor(s), FD is 2816
  Descriptor Blocks:
  0.0.0.0 (Null0), from 0.0.0.0, Send flag is 0x0
      Composite metric is (2816/0), route is Internal
      Vector metric:
        Minimum bandwidth is 1000000 Kbit
        Total delay is 10 microseconds
        Reliability is 255/255
        Load is 1/255
        Minimum MTU is 1500
        Hop count is 0
        Originating router is 10.0.0.1

Those are the values that the summary address use when g0/2 is up so we'll use them with the "summary-metric" command


R1(config)#router eigrp 100
R1(config-router)#summary-metric 10.0.0.0/23 1000000 1 255 1 1500

We had to divide by 10 the delay cause it has to be in ten microsends


That's it, everytime we shutdown the interface g0/2 on R1, the metric in R2 to reach 10.0.0.0/23 will remain the same


R2#sh ip route
 D 10.0.0.0 [90/3072] via 1.1.1.1, 00:03:59, GigabitEthernet1



I use cisco virl for these labs but i think they will work ok in GNS3 too.

Please leave your feedback