# EIGRP IPv4

## EIGRP Basics

Begriffe und Konzepte in EIGRP

1. Feasible Distance (FD)
- Die Feasible Distance ist der metrische Gesamtwert (also die "Kosten"), die ein Router berechnet, um ein Zielnetzwerk zu erreichen.
    
    Sie setzt sich zusammen aus:
    
- Metrik zum direkten Nachbarn (next-hop)
- Metrik, die dieser Nachbar selbst bis zum Zielnetzwerk hat
- Es ist also die Gesamtkosten-Schätzung von deinem Router bis zum Zielnetzwerk – über einen bestimmten Nachbarn.
1. Reported Distance (RD)
- Die Reported Distance (auch bekannt als "Advertised Distance") ist die Metrik, die ein Nachbarrouter selbst zu einem Zielnetzwerk hat – also was er dir "meldet".
- Diese ist ein wichtiger Vergleichswert zur Berechnung des Feasible Successors.
1. Successor
- Der Successor ist der beste Pfad zum Zielnetzwerk – also der mit der niedrigsten Feasible Distance.
- Dieser Pfad wird immer in die Routing-Tabelle aufgenommen.
1. Feasible Successor (FS)
- Ein Feasible Successor ist ein Backup-Pfad zum Zielnetzwerk.
- Voraussetzung: Seine Reported Distance (RD) muss kleiner sein als die Feasible Distance (FD) des aktuellen Successors.> Das stellt sicher, dass der FS loop-free ist – also keine Routing-Schleifen entstehen können.

## Classic Configuration with Autonomous System 100

```
router eigrp 100
    eigrp router-id 2.2.2.2
  network 10.10.10.0 255.255.255.0
```

## Named Configuration with Autonomous System 100 (better option)

```
router eigrp LAB-EIGRP
    address-family ipv4 unicast autonomous-system 100
    eigrp router-id 1.1.1.1
    network 10.10.20.0 255.255.255.0
```

## Additional Configuration

### Stop unnecessary EIGRP neighbor discovery (Named)

```
router eigrp LAB-EIGRP
    address-family ipv4 unicast autonomous-system 100
    af-interface default
      passive-interface
      exit
    af-interface g0/1
      no passive-interface
      exit
```

### Stop unnecessary EIGRP neighbor discovery (classic)

```
router eigrp 100
    passive-interface default
  no passive-interface g0/0
  no passive-interface g0/1
```

### Authentication (on interface)

For MD5 classic and all connected to classic (you cannot mix sha256 and md5)

```
key chain EIGRP-AUTHEN-KEY
    key 1
  key-string mysecret
  exit

int g0/0
    ip authentication key-chain eigrp 100 EIGRP-AUTHEN-KEY
  ip authentication mode eigrp 100 md5
  exit
```

Named configuration also supports SHA256!!!

```
router eigrp LAB-EIGRP
    address-family ipv4 unicast autonomous-system 100
    af-interface g0/1
      authentication mode hmac-sha-256 mysupersecuresecret
      exit
```

### Load balancing and variance

Maybe adjust the brandwith on the interfaces

Allow routes with up to double RD:

```
router eigrp LAB-EIGRP
    address-family ipv4 unicast autonomous-system 100
    topology base
      variance 2
      exit
```

Otherwise only the equal to best distances will be taken into account.

### Timers (Named)

```
router eigrp LAB-EIGRP
    address-family ipv4 unicast autonomous-system 100
    af-interface g0/0
      hello-interval 10
      hold-time 30
```

### Timers (classic)

```
int g0/1
    ip hello-interval eigrp 100 10
  ip hold-time eigrp 100 30
```

### Summary Addresses

Summaries need to be placed on the interfaces that distribute routes, e.g. Int g0/0 has multiple Sub-interfaces and Int g0/1 is also a "Client"network, Int g0/2 is distributing all local networks into EIGRP summarized. If S1/0/1 is also connected to the EIGRP process, proceed accordingly.

Named:

```
router eigrp LAB-EIGRP
    address-family ipv4 unicast autonomous-system 100
    af-interface g0/2
      summary-address 10.10.0.0 255.255.0.0
       exit
```

Classic:

```
int g0/2
    ip summary-address eigrp 100 10.10.0.0 255.255.0.0
```

### Stub setup to reduce forwarding of queries with guranteed no-answer

Named:

```
router eigrp LAB-EIGRP
    address-family ipv4 unicast autonomous-system 100
    eigrp stub
    exit
```

Classic:

```
router eigrp 100
    eigrp stub
  exit
```

### Filtered Distribute List

Filter out a network from being updated to a peer.

Named:

```
ip acess-list standard EIGRP-FILTER
    deny 10.10.0.0 0.0.255.255
  permit any
  exit

router eigrp LAB-EIGRP
    address-family ipv4 unicast autonomous-system 100
    topology base
    distribute-list EIGRP-FILTER out g0/2
    exit
```

Classic:

```
ip access-list standard EIGRP-FILTER
    deny 10.10.0.0 0.0.255.255
  permit any
  exit

router eigrp 100
    distribute-list EIGRP-FILTER out g0/2
  exit
```

# EIGRP IPv6

IPv6 unicast-routing MUST BE ENABLED

On IPv6 ONLY devices, the router-id must be set

## Classic Configuration with Autonomous System 100

```
ipv6 router eigrp 100
    eigrp router-id 2.2.2.2
    exit
int g0/0
    ipv6 eigrp 100
  exit
int g0/1
    ipv6 eigrp 100
  exit
int lo1
    ipv6 eigrp 100
  exit
```

## Named Configuration with Autonomous System 100 (better option)

```
router eigrp LAB-EIGRP
    address-family ipv6 unicast autonomous-system 100
    eigrp router-id 2.2.2.2
```

Now it is enabled on all interfaces by default (that have IPv6 configured). Adjust:

```
router eigrp LAB-EIGRP
    address-family ipv6 unicast autonomous-system 100
    af-interface default
      passive-interface
      exit
    af-interface lo1
      shutdown
      exit
    af-interface g0/0
      no passive-interface
      exit
```

## Additional Configuration

### Passive Interfaces

for Named above

Classic:

```
ipv6 router eigrp 100
    passive-interface default
  no passive-interface g0/0
  no passive-interface g0/1
  exit
```

### Redistribution of routes

Classical:

```
ipv6 route ::/0 2001:db8:acad::1:2

ipv6 router eigrp 100
    redistribute static
  exit
```

Named:

```
router eigrp LAB-EIGRP
    address-family ipv6 unicast autonomous-system 100
    topology base
      redistribute static
      exit
```

### Summary Adresses

Alternative default gateway advertisement:

Classic:

```
int g0/0
    ipv6 summary-address eigrp 100 ::/0
  exit
```

Named:

```
router eigrp LAB-EIGRP
    address-family ipv6 unicast autonomous-system 100
    af-interface g0/0
      summary-address 2001:db8:abcd::/56
      exit
```

### Authentication (on interface)

Classic only allows MD5, Named adds support for SHA256

Classic:

```
key chain EIGRPv6-AUTHEN-KEY
    key 1
  key-string mysecret
  exit

int g0/0
    ipv6 authentication key-chain eigrp 100 EIGRPv6-AUTHEN-KEY
  ipv6 authentication mode eigrp 100 md5
```

Named:

```
key chain EIGRPv6-AUTHEN-KEY
    key 1
  key-string mysecret
  exit

router eigrp LAB-EIGRP
    address-family ipv6 unicast autonomous-system 100
    af-interface g0/0
      authenication key-chain EIGRPv6-AUTHEN-KEY
      authentication mode md5
      exit
    af-interface g0/1
      authentication mode hmac-sha-256 mysupersecuresecret
      exit
```

### Load balancing and variance

Utilizing maximum-paths to setup up to 32 instead of 4 destinations

Adjust brandwith again (for example to 800000)

```
router eigrp LAB-EIGRP
    address-family ipv6 unicast autonomous-system 100
    topology base
      variance 2
      exit
```

### Filter with prefix list

Classic:

```
ipv6 prefix-list DROP-BRANCH-1 seq 10 deny 2001:db8:cafe:1::/64
ipv6 prefix-list DROP-BRANCH-1 seq 20 permit ::/0

ipv6 router eigrp 100
    distribute-list prefix-list DROP-BRANCH-1 out g0/1
  exit
```

Named:

```
ipv6 prefix-list DROP-BRANCH-1 seq 10 deny 2001:db8:cafe:1::/64
ipv6 prefix-list DROP-BRANCH-1 seq 20 permit ::/0

router eigrp LAB-EIGRP
    address-family ipv6 unicast autonomous-system 100
    topology base
      destribute-list prefix-list DROP-BRANCH-1 out g0/1
      exit
```

# Redistribution

## OSPF into EIGRP

Redistribute OSPF routes into EIGRP

```
router eigrp 100
    redistribute ospf 100 metric 10000 100 255 1 1500
  exit
```

```
router eigrp LAB-EIGRP
    address-family ipv4 unicast autonomous-system 100
    topology base
      redistribute ospfv3 100 metric 1000000 10 255 1 1500
      exit
    exit
  address-family ipv6 autonomous-system 100
    topology base
      default-metric 1000000 10 255 1 1500
      redistribute ospf 100
      ! assumes opsfv3 since in an IPv6 AF
      ! optionally with include-connected
```

Routes redistributed into EIGRP require emtrics to be set.

### ACLs

Filter a network from being redistributed into EIGRP from OSPF

```
ip access-list standard OSPF-FILTER
    remark Used with DList to filter OSPF
  deny <network> <wildcard>
  permit any
  exit

router eigrp 100
    distribute-list OSPF-FILTER out ospf 100
```

### Filtering using route maps

```
ip access-list standard LOOP-ACL
    permit 10.10.10.10 0.0.0.0
  permit 10.10.10.11 0.0.0.0
  exit
route-map LOOP-FILTER deny 10
    match ip address LOOP-ACL
  exit
route-map LOOP-FILTER permit 20
    exit

router eigrp 100
    redistribute ospf 100 route-map LOOP-FILTER metric 1000000 100 255 1 1500
  exit
```

## EIGRP into EIGRP

One-way redistribution:

```
router eigrp 100
    redistribute eigrp 50
```

Now EIGRP AS 100 obtains the routes from EIGRP 50 while 50 does NOT btain the routes from 100.

```
router eigrp LAB-EIGRP
    address-family ipv4 unicast autonomous-system 50
    topology base
      redistribute eigrp 100
       exit
```

Now a two-way redistribution is established

Only allow some networks to be sent towards a peer on a specific interface:

Default route and a network

```
ip prefix-list FILTER-INT seq 5 permit 0.0.0.0/0
ip prefix-list FILTER-INT seq 10 permit 10.1.1.0/24
ip prefix-list FILTER-INT seq 15 deny 0.0.0.0/0 le 32

router eigrp 100
    distribute-list prefix FILTER_INT out <int>
  exit
```

## EIGRP Authentication

Sonstiges:

Classic EIGRP supports key-chain based MD5-hashed keys, while Named EIGRP adds support for SHA256-hashed keys. The two are not compatible.

Keychain erstellen

```
key chain EIGRP-AUTH-KEY
  key 1
  key-string cisco123
```

Named EIGRP

```
router eigrp WSC2024
  address-family ipv4 autonomous-system 24
    af-interface gig0/1
    authentication key-chain EIGRP-AUTH-KEY
    authentication mode md5
```

Standard EIGRP

```
Interface gig0/1
  ip authentication key-chain eigrp 24 EIGRP-AUTH-KEY
  ip authentication mode eigrp 24 md5
```

## Unequal Cost Load Balancing mit variance

EIGRP balanciert standardmäßig nur über Pfade mit gleichen Kosten (gleicher FD). OSPF ebenfalls.

Was macht variance?

- Variance ist ein Multiplikator, der entscheidet, welche zusätzlichen Pfade mit in die Routing-Tabelle aufgenommen werden dürfen – auch wenn sie nicht gleich teuer sind wie der beste Pfad.
- Standardwert ist 1, was bedeutet: Nur gleich teure Pfade (FD gleich der besten FD) dürfen genutzt werden.

Beispiel:

Bester Pfad (FD) = 1000

Zweitbester Pfad (FD) = 1400

variance = 2 → erlaubt Pfade mit FD ≤ 1000 × 2 = 2000 → also auch 1400

Konfiguration:

Beispiel:

```
R3# show ip eigrp topology | section 192.168.1.0
        P 192.168.1.0/24, 1 successors, FD is **2621440**
        via 172.16.13.2 (**2621440**/1966080), GigabitEthernet0/0/1
        via 10.0.23.2 (2785280/2129920), GigabitEthernet0/0/0
```

- Die Route über 10.0.23.2 taucht nicht im Routing Table auf, weil die FD zu groß ist. (wegen 100mbit Verbindung)
- Durch "variance 2" (2621400 x 2 = 5242880) ist 2785280 ebenfalls kleiner oder gleich 5242880

```
router eigrp BASIC-EIGRP-LAB
    address-family ipv4 unicast autonomous-system 27
  topology base
    variance 2
    end
```