Facts to remember about EIGRP

EIGRP Filtering with Passive Interface

• The passive-interface command in EIGRP, stops the sending of updates out an interface. Unlike RIPv2, however, passive-interface in EIGRP will prevent forming of an adjacency on the interface because it stops sending EIGRP Hello packets as well
• The passive-interface default command can be used to make all interfaces passive, and then interfaces can have the passive feature selectively disabled with the no passive-interface command

R9:
router eigrp 100
 passive-interface default
 no passive-interface GigabitEthernet1.79

EIGRP MD5 & SHA-256 Authentication

• MD5 authentication in classic mode is applied at link level

SW1:
key chain SW1_KEY
 key 0
   key-string SW!_Key
!
interface Vlan121
 ip authentication mode eigrp 1 md5
 ip authentication key-chain eigrp 1 SW1_KEY
!

• MD5 authentication in Multi-AF (Named) Mode is applied at the af-interface mode 
• SHA-256 authentication can also be applied in name mode but it didn't support "key chains"
• In EIGRP Named Mode options applied to all links at the same time can be configured at the "af-interface default". Within the scope of authentication, this can be used to configure a default key for all interfaces, or a default fallback key for interfaces that do not have a specific key applied:

key chain MD5_KEYS
 key 1
   key-string MD5_PASS
!
router eigrp MULTI-AF
 !
 address-family ipv4 unicast autonomous-system 100
  !
  af-interface Tunnel0
   authentication mode hmac-sha-256 SHA_KEY
  exit-af-interface
  !
  af-interface GigabitEthernet1.146
   authentication mode md5
   authentication key-chain MD5_KEYS
  exit-af-interface

router eigrp MULTI-AF
 !
 address-family ipv4 unicast autonomous-system 100
  !
  af-interface default
   authentication mode hmac-sha-256 SHA_DEFAULT
  exit-af-interface
  !

How to make a stub router a transit router

In an EIGRP network you have been asked to make R8 a stub router (it will not receive QUERIES and it will not advertise other networks), If you do that R10 will not know how to reach other routes cause depends on R8. Your job is to configure R8 as a stub router but at the same time as a transit router for  R10. They also asked you that R8 advertises its connected routes

This is the configuration to make R8 a stub router and at the same time to advertise connected routers

router eigrp 100
 eigrp stub connected


A route by default to R8 would resolve the problem about R10 isolation. but how to spread a default route just for R10 ?.  doing a summary address by interface

conf term
interface g1.108
ip summary-address eigrp 100 0.0.0.0 0.0.0.0


Now R10 is using R8 as a default route. The problem now is R8 have a default route pointing to null with 5 as administrative distance, This is a default in EIGRP when we do a summary.

show ip route
D*    0.0.0.0/0 is a summary, 00:00:07, Null0

This default route will be replaced if we add a static default route (pointing to R5), cause static routes have 1 as administrative distance which is a better route

conf term
ip route 0.0.0.0 0.0.0.0 155.1.58.5

There we go, the only thing we have left is to tell R8 to advertise summary routes too,

router eigrp 100
 eigrp stub connected summary

Now R8 is a stub router and at the same time is a transit router only for R10

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