UE4 – Protocoles de Routage

Présentation au sujet: "UE4 – Protocoles de Routage"— Transcription de la présentation:

1 UE4 – Protocoles de Routage
La Table de Routage

2 La Structure d’une Table de Routage
La structure d’une table de routage semble évidente Connaître le fonctionnement d’une table de routage peut être très utile lors d’un dépannage ou pour vérifier une configuration Router# show ip route /24 is subnetted, 4 subnets S is directly connected, Serial0/0/1 R [120/1] via , 00:00:08, Serial0/0/0 C is directly connected, Serial0/0/0 C is directly connected, FastEthernet0/0 /16 is subnetted, 1 subnets S is directly connected, Serial0/0/1 C /24 is directly connected, Serial0/0/1 S /24 is directly connected, Serial0/0/1 The structure of the routing table might seem obvious. Help you verify and troubleshoot routing issues because you will understand the routing table lookup process. You will know exactly what the Cisco IOS software does when it searches for a route.

3 Quelques exemples Différents types de route selon leurs sources
Réseaux directement connectés Routes statiques Protocoles de routage dynamique La source des routes n’affecte pas la structure de la table de routage Router# show ip route /24 is subnetted, 4 subnets S is directly connected, Serial0/0/1 R [120/1] via , 00:00:08, Serial0/0/0 C is directly connected, Serial0/0/0 C is directly connected, FastEthernet0/0 /16 is subnetted, 1 subnets S is directly connected, Serial0/0/1 C /24 is directly connected, Serial0/0/1 S /24 is directly connected, Serial0/0/1 Route entries from the following sources: Directly connected networks Static routes Dynamic routing protocols The source of the route does not affect the structure of the routing table

4 Quelques exemples L’hiérarchie des tables de routage IOS a été initialement implémentée avec un schéma de routage classful La table de routage incorpore les deux mécanismes, classful et classless Router# show ip route /24 is subnetted, 4 subnets S is directly connected, Serial0/0/1 R [120/1] via , 00:00:08, Serial0/0/0 C is directly connected, Serial0/0/0 C is directly connected, FastEthernet0/0 /16 is subnetted, 1 subnets S is directly connected, Serial0/0/1 C /24 is directly connected, Serial0/0/1 S /24 is directly connected, Serial0/0/1 Adresse Classful The routing table hierarchy in Cisco IOS software was originally implemented with the classful routing scheme. Although the routing table incorporates both classful and classless addressing, the overall structure is still built around this classful scheme. Sous-réseaux

5 Topologie pour l’exemple à venir
Notice that R3 also has a /24 subnet that is disconnected, or discontiguous, from the network that R1 and R2 share. The effects of this discontiguous subnet are examined later in this chapter when you look at the route lookup process.

6 Configurations des interfaces de R1 et R3
Pour l’instant on ne configure pas les interfaces de R2 R1(config)# interface FastEthernet0/0 R1(config-if)# ip address R1(config-if)# no shutdown R1(config-if)# interface Serial0/0/0 R1(config-if)# ip address R1(config-if)# clock rate 64000 R3(config)# interface FastEthernet0/0 R3(config-if)# ip address R3(config-if)# no shutdown R3(config-if)# interface Serial0/0/1 R3(config-if)# ip address

7 Routes de Niveau 1 Dès qu’on entre « no shutdown », la sortie de debug ip routing indique que cette route a été rajoutée à la table de routage R2# debug ip routing IP routing debugging is on R2# conf t R2(config)# interface serial 0/0/1 R2(config-if)# ip address R2(config-if)# clock rate 64000 R2(config-if)# no shutdown R2(config-if)# 00:11:06: %LINK-3-UPDOWN: Interface Serial0/0/1, changed state to up RT: add /24 via , connected metric [0/0] RT: interface Serial0/0/1 added to routing table R2(config-if)# end R2# undebug all All possible debugging has been turned off Serial 0/0/1 interface for R2 is configured with the /24 address As soon as no shutdown is entered, the output from debug ip routing shows that this route has been added to the routing table.

8 Routes de Niveau 1 La table de routage est une structure hiérarchique qui est censée accélérer la recherche d’une route lors de la transmission de paquets Dans cette hiérarchie, on y trouve plusieurs niveaux Pour simplicité, nous étudions toutes les routes en seulement deux niveaux RT: add /24 via , connected metric [0/0] RT: interface Serial0/0/1 added to routing table R2(config-if)# end R2# show ip route <output omitted> C /24 is directly connected, Serial0/0/1 The routing table is actually a hierarchical structure that is used to speed up the lookup process when locating routes and forwarding packets. Within this structure, the hierarchy includes several levels. For simplicity, we discuss all routes as one of two levels: level 1 or level 2.

9 Routes de Niveau 1 Une route de niveau 1 est une route avec un masque de sous-réseau égal ou inférieur au masque par défaut de la classe de l’adresse R2# show ip route <output omitted> C /24 is directly connected, Serial0/0/1 Celle-ci est une route niveau 1 L’adresse appartient à la classe C Le masque est égal ou inférieur à celui de la classe C A level 1 route is a route with a subnet mask equal to or less than the classful mask of the network address. /24 is a level 1 network route because the subnet mask is equal to the network’s classful mask. /24 is the classful mask for Class C networks, such as the network.

10 Routes de Niveau 1 Une route de niveau 1 peut être utilisée pour : Route par défaut: Une route par défaut est une route statique avec l’adresse /0 Route agrégée (supernet) : Une route avec un masque inférieur à celui de la classe du réseau Route pour un réseau : Une route avec un masque égal à celui de la classe du réseau A level 1 route can function as any of the following: Default route: A default route is a static route with the address /0. Supernet route: A supernet route is a network address with a mask less than the classful mask. Network route: A network route is a route that has a subnet mask equal to that of the classful mask. A network route can also be a parent route (next).

11 Routes de Niveau 1 La route de niveau /24 peut être aussi appelée « route définitive » (ultimate route) Une route définitive est une route qui inclut une ou toutes caractéristiques : Une adresse de prochain saut (next-hop) Une interface de sortie The level 1 route /24 can be further defined as an ultimate route. An ultimate route is a route that includes one or both of the following: A next-hop IP address (another path) An exit interface

12 Routes de Niveau 1 Comment on sait que la route directement connectée /24 : Est une route de niveau 1 ? Le masque du réseau est égal à celui de la classe Est une route définitive ? Contient l’interface de sortie Serial 0/0/1. Classe C Interface de Sortie Directly connected network /24 is a level 1 network route - subnet mask that is the same as its classful mask. ultimate route - contains the exit interface Serial 0/0/1.

13 Routes Parent et Enfant : Réseaux Classful
Un autre type de route niveau 1 est la route parent Lorsque le réseau a été rajouté, une entrée supplémentaire a été créée Que peut-on dire des routes parent de niveau 1 ? Aucune adresse de prochain saut ou interface de sortie sont indiquées R2(config)# interface fastethernet 0/0 R2(config-if)# ip address R2(config-if)# no shutdown R2(config-if)# end R2# show ip route Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, <text omitted> Gateway of last resort is not set /24 is subnetted, 1 subnets C is directly connected, FastEthernet0/0 C /24 is directly connected, Serial0/0/1 Another type of level 1 network route, a parent route. When the subnet was added to the routing table, Another route, also added. First entry: no next-hop IP address or exit interface information. This route is known as a level 1 parent route. Route Parent de Niveau 1

14 Routes Parent et Enfant : Réseaux Classful
Une route parent est une entête qui : Indique la présence de routes niveau 2, aussi connues comme routes enfant Une route parent de niveau 1 est créée automatiquement lorsqu’on rajoute un sous- réseau à la table de routage Une route parent est créée à chaque fois qu’une route avec un masque plus grand que celui de la classe est entrée dans la table de routage R2# show ip route Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, <text omitted> Gateway of last resort is not set /24 is subnetted, 1 subnets C is directly connected, FastEthernet0/0 C /24 is directly connected, Serial0/0/1 A parent route is a heading: Indicates the presence of level 2 routes, also known as child routes. A level 1 parent route is automatically created any time a subnet is added to the routing table. A parent route is created whenever a route with a mask greater than the classful mask is entered into the routing table. The subnet is the level 2 child route of the parent route Route Parent niveau 1 Route enfant niveau 2

15 Routes Parent et Enfant : Réseaux Classful
Comme une route niveau 1, la source d’une route niveau 2 peut être : Un réseau directement connecté Une route statique Une route dynamique (avec un protocole classful ou classless) Route parent niveau 1 Route enfant niveau 2 A level 2 route is a route that is a subnet of a classful network address. Like a level 1 route, the source of a level 2 route can be a : directly connected network static route dynamic routing protocol. Note: This is the case even if a classless routing protocol is the source of the subnet route.

16 Routes Parent et Enfant : Réseaux Classful
Parent route: : The classful network address for our subnet. /24: The subnet mask for all the child routes. If the child routes have variable-length subnet masks (VLSM), the subnet mask will be excluded from the parent route and included with the individual child routes. (later). is subnetted, 1 subnets: This part of the route specifies that this is a parent route and in this case has one child route (that is, one subnet).

17 Route Enfant The subnet mask for this child route is the /24 mask included in its parent route, Child route: C: The route code for a directly connected network. : The specific route entry. is directly connected: Along with the route code of C, this specifies that this is a directly connected network with an administrative distance of 0. FastEthernet0/0: The exit interface for forwarding packets that match this specific route entry.

18 Rajouter une autre route enfant
Nous allons configure une autre interface Attention à l’endroit où cette route sera insérée Comme toutes les routes enfant ont le même masque, la route parent gardera le masque /24 mais indique désormais deux routes R2(config)# interface serial 0/0/0 R2(config-if)# ip address R2(config-if)# no shutdown R2(config-if)# end R2# show ip route /24 is subnetted, 2 subnets C is directly connected, Serial0/0/0 C is directly connected, FastEthernet0/0 C /24 is directly connected, Serial0/0/1 The routing table shows two child routes for the same /24 parent route. and are members both members of the /16 classful network. Because both child routes have the same subnet mask, the parent route still maintains the /24 mask but now shows two subnets. Later we will see the role of the parent route.

19 Suppression de toutes les routes enfant
Si toutes les routes enfant sont effacées alors la route parent le sera aussi If there is only a single level 2 child route and that route is removed, the level 1 parent route is automatically deleted. A level 1 parent route exists only when there is at least one level 2 child route.

20 Routes Parent et Enfant : Réseaux Classless
Pour illustrer ce cas, on change temporairement de topologie For this discussion, we switch briefly to the RouterX topology.

21 Routes Parent et Enfant : Réseaux Classless
On observe que les routes enfant ne partagent pas le même masque, comme c’était le cas dans les réseaux classful RouterX# show ip route /16 is variably subnetted, 3 subnets, 2 masks C /30 is directly connected, Serial0/0/0 C /30 is directly connected, Serial0/0/1 C /24 is directly connected, FastEthernet0/0 All three subnets belong to the classful network /16 and are therefore level 2 child routes. Notice that the child routes do not share the same subnet mask, as was the case in the classful example. Implementing a network addressing scheme with VLSM. Whenever there are two or more child routes with different subnet masks belonging to the same classful network, the routing table presents a slightly different view, which states that this parent network is variably subnetted.

22 Routes Parent et Enfant : Réseaux Classless
The parent route of now contains the classful mask /16. In the classful example shown earlier the classful mask was not displayed. Parent route states that the child routes are variably subnetted. Includes the number of different masks of the child routes (2 masks). Each child route now contains the subnet mask for that specific route. In the non-VLSM example both child routes shared the same subnet mask, and the parent displayed their common subnet mask. Parent route: : The parent route, the classful network address associated with all child routes /16: The classful subnet mask of the parent route variably subnetted: States that the child routes are variably subnetted and that there are multiple masks for this classful network 3 subnets, 2 masks: Indicates the number of subnets and the number of different subnet masks for the child routes under this parent route Child route: C: The route code for a directly connected network : The specific route entry /30: The subnet mask for this specific route is directly connected: Along with the route code of C, specifies that this is a directly connected network with an administrative distance of 0 Serial0/0/0: The exit interface for forwarding packets that match this specific route entry

23 Fonctionnement de la table de routage
Paquet IP Table de Routage When a router receives a packet on one of its interfaces. The routing table lookup process compares the destination IP address of the incoming packet with the entries in the routing table. The best match between the packet’s destination IP address and the route in the routing table is used to determine to which interface to forward the packet. Trouver la meilleure correspondance

24 Configuration de RIPv1 Pour illustration, nous choisissons un protocole classful qui ne supportera pas le réseau non- contigu R1(config)# router rip R1(config-router)# network R2(config)# router rip R2(config-router)# network R2(config-router)# network R3(config)# router rip R3(config-router)# network R3(config-router)# network We have specifically chosen a classful routing protocol with our discontiguous subnets. The reason for this will become evident in a later section.

25 Étapes du processus de routage
Ni R1 ni R2 ont des routes pour R1# show ip route /24 is subnetted, 3 subnets C is directly connected, FastEthernet0/0 C is directly connected, Serial0/0/0 R [120/1] via , 00:00:25, Serial0/0/0 R /24 [120/1] via , 00:00:25, Serial0/0/0 R2# show ip route /24 is subnetted, 3 subnets R [120/1] via , 00:00:07, Serial0/0/0 C is directly connected, Serial0/0/0 C is directly connected, FastEthernet0/0 C /24 is directly connected, Serial0/0/1 Neither R1 nor R2 has a route to Also, R3 does not have routes to subnets /24, /24, or /24. R3# show ip route /24 is subnetted, 1 subnets C is directly connected, FastEthernet0/0 C /24 is directly connected, Serial0/0/1

26 Le processus du routage
Table de Routage Étape 1. Le routeur examine les routes de niveau 1 Step 1. The router examines level 1 routes, including network routes and supernet routes, for the best match with the destination address of the IP packet

27 Le processus du routage
Table de Routage Étape 1a. Si la meilleure correspondance est une route définitive de niveau 1 – un réseau classful, un supernet ou une route par défaut – cette route sera choisie If the best match is a level 1 ultimate route—a classful network, supernet, or default route—this route is used to forward the packet

28 Le processus du routage
Table de Routage Étape 1b. Si la meilleure correspondance est une route parent de niveau 1, avancer à l’étape 2 Étape 2. Le route examine les routes enfant (les sous-réseaux) de cette route parent à la recherche d’une correspondance Step 1b. If the best match is a level 1 parent route, proceed to Step 2 Step 2. The router examines child routes (the subnet routes) of the parent route for a best match.

29 Le processus du routage
Table de Routage Étape 2a. Si une correspondance avec une route niveau 2 est trouvée, celle-ci sera utilisée Step 2a. If there is a match with a level 2 child route, that subnet is used to forward the packet.

30 Le processus du routage
Table de routage Étape 2b. Si aucune correspondance avec une route niveau 2 est trouvée, procéder à l’étape 3 Step 2b. If there is not a match with any of the level 2 child routes, proceed to Step 3.

31 Le processus du routage
Table de routage Étape 3. Quel est le comportement du routeur ? (classful ou classless) Router(config)# no ip classless Router(config)# ip classless Step 3. Is the router implementing classful or classless routing behavior. (later) Router(config)# no ip classless Router(config)# ip classless

32 Le processus du routage
Table de routage Étape 3a. Si le comportement classful est actif, terminer le processus et jeter le paquet Router(config)# no ip classless Step 3a. If classful routing behavior is in effect, terminate the lookup process and drop the packet. Router(config)# no ip classless

33 Le processus du routage
Table de routage Étape 3b. Si le comportement classless est actif, continuer à chercher un supernet dans les routes niveau 1, voir une route par défaut si disponible Router(config)# ip classless Step 3b. If classless routing behavior is in effect, continue searching level 1 supernet routes in the routing table for a match, including the default route, if there is one.

34 Le processus du routage
Table de routage Étape 4. Correspondance – transmission du paquet Étape 5. Aucune correspondance – jeter le paquet Step 4. If there is now a lesser match with a level 1 supernet or default routes, the router uses that route to forward the packet. Step 5. If there is not a match with any route in the routing table, the router drops the packet.

35 Note : Modifier le comportement IOS
Si un protocole classless tel que OSPF est en utilisation, les autres routes seront examinées même si aucune correspondance est trouvée au niveau des routes enfant Ceci arrive indépendamment d’utiliser ip classless ou no ip classless Tourner un protocole classless est une manière de dépasser le no ip classless

36 Exemple : classful Destination du paquet : 172.30.4.1
RTC(config)# no ip classless RTC#show ip route Gateway of last resort is to network R /24 [120/1] via , 00:00:02, Serial1 C /24 is directly connected, Serial1 C /24 is directly connected, Ethernet0 /24 is subnetted, 3 subnets C is directly connected, Loopback1 C is directly connected, Loopback2 C is directly connected, Loopback3 S* /0 [1/0] via RTC#ping Sending 5, 100-byte ICMP Echoes to , timeout is 2 seconds: ..... Success rate is 0 percent (0/5) Destination du paquet :

37 Exemple : classless Destination du paquet : 172.30.4.1
RTC(config)# ip classless RTC# show ip route Gateway of last resort is to network R /24 [120/1] via , 00:00:02, Serial1 C /24 is directly connected, Serial1 C /24 is directly connected, Ethernet0 /24 is subnetted, 3 subnets C is directly connected, Loopback1 C is directly connected, Loopback2 C is directly connected, Loopback3 S* /0 [1/0] via RTC#ping Sending 5, 100-byte ICMP Echoes to , timeout is 2 seconds: !!!!! Success rate is 100 percent (5/5),round-trip min/avg/max=56/57/60 ms Destination du paquet :

38 Correspondance la plus grande
Le masque d’une route dans la table de routage est utilisé pour déterminer le nombre minimum de bits qui doivent correspondre (Digressing from topology) For there to be a match between the destination IP address of a packet and a route in the routing table, a minimum number of leftmost bits must match between the IP address of the packet and the route in the routing table. The subnet mask of the route in the routing table is used to determine the minimum number of leftmost bits that must match. IP packet only contains the IP address and not the subnet mask.

39 Meilleure correspondance
La meilleure correspondance est la route dans la table de routage qui contient le plus grand nombre de bits en commun avec l’adresse IP du paquet Quelle est la meilleure route ? The best match or longest match is the route in the routing table that has the greatest number of leftmost matching bits with the destination IP address of the packet. The route with the greatest number of equivalent leftmost bits, or the longest match, is always the preferred route. Subnet mask in routing table specifies the minimum number of leftmost matching bits – the only bits that are considered. All three routes match but Route 3 has the longest match.

40 Exemple : Route définitive de niveau 1

41 Exemple : Route définitive de niveau 1
PC1 envoie un ping à , l’interface série de R3 PC1 sends a ping to , the serial interface on R3. R1# show ip route /24 is subnetted, 3 subnets C is directly connected, FastEthernet0/0 C is directly connected, Serial0/0/0 R [120/1] via , 00:00:25, Serial0/0/0 R /24 [120/1] via , 00:00:25, Serial0/0/0

42 Le routeur examine d’abord les routes niveau 1 pour trouver une correspondance
R1# show ip route /24 is subnetted, 3 subnets C is directly connected, FastEthernet0/0 C is directly connected, Serial0/0/0 R [120/1] via , 00:00:25, Serial0/0/0 R /24 [120/1] via , 00:00:25, Serial0/0/0 The router first examines level 1 routes for the best match. R1# show ip route /24 is subnetted, 3 subnets R /24 [120/1] via , 00:00:25, Serial0/0/0

43 Une correspondance est trouvée entre l’adresse destination 192. 168. 1
Une correspondance est trouvée entre l’adresse destination et la route définitive de /24 There is a match between the destination IP address and the level 1 ultimate route of /24. R1 uses this route and forwards the packet out interface Serial 0/0/0. R1# show ip route /24 is subnetted, 3 subnets R /24 [120/1] via , 00:00:25, Serial0/0/0

44 Exemple : Route définitive de niveau 1
Pourquoi avoir choisi la route niveau /24 au lieu de regarder les sous- réseaux de ? Car il faut un minimum de correspondance ! Why is there a match with the /24 level 1 route and not with one of the subnets? Why is there not a match with any of the /24 subnets in the routing table? /24 is a parent route of three subnets or child routes. Before a child route is examined for a match, there must be at least a match between the destination IP address of the packet and the classful address of the parent route, or /16. 16 bits (/16) must match the route /16 – no match!

45 Exemple : Route définitive de niveau 1
La route choisie respecte le minimum de 24 bits. Il y a même 30 bits en commun ! The route, , is a level 1 ultimate route and, therefore, it also contains the subnet mask, /24. Not only does the minimum of 24 bits match, but a total of 30 bits match. Because there is not a longer, more specific match, the packet is forwarded out the exit interface Serial 0/0/0.

46 Exemple : Route définitive de niveau 1
R1 transfère le paquet via Serial0/0/0. R1 forwards the packet out Serial0/0/0. R1# show ip route /24 is subnetted, 3 subnets C is directly connected, FastEthernet0/0 C is directly connected, Serial0/0/0 R [120/1] via , 00:00:25, Serial0/0/0 R /24 [120/1] via , 00:00:25, Serial0/0/0 nop ici

47 Meilleure correspondance : routes niveau 1 et 2

48 La première correspondance trouvée est celle de la route parent niveau 1 172.16.0.0
The first match that occurs is with the level 1 parent route, With non-VLSM subnets, the classful mask of the parent is not displayed. Before any child routes (subnets) are examined for a match, there must be a match with the classful address of the parent route. Because is a Class B address, 16 leftmost bits must match. 16 bits match the parent route, R1# show ip route /24 is subnetted, 3 subnets C is directly connected, FastEthernet0/0 C is directly connected, Serial0/0/0 R [120/1] via , 00:00:25, Serial0/0/0 R /24 [120/1] via , 00:00:25, Serial0/0/0 Ok

49 Comme on a une correspondance avec la route parent, les routes enfant seront examinées à la recherche d’une correspondance Le masque /24 indique le nombre minimum de bits qui doivent correspondre Because there is a match with the parent route, the level 2 child routes will be examined for a match. The actual subnet mask of /24 is used for the minimum number of leftmost bits that must match. R1# show ip route /24 is subnetted, 3 subnets C is directly connected, FastEthernet0/0 C is directly connected, Serial0/0/0 R [120/1] via , 00:00:25, Serial0/0/0 R /24 [120/1] via , 00:00:25, Serial0/0/0 Vérifie les routes enfant

50 Le processus de recherche regarde les routes enfant
Le processus de recherche regarde les routes enfant. Des trois sous-réseaux, seulement un a une correspondance à 24 bits The route lookup process searches the child routes for a match. In this case, there must be a minimum of 24 bits that match. Of the three subnets there is only one route that has 24 bits that match: R1# show ip route /24 is subnetted, 3 subnets C is directly connected, FastEthernet0/0 C is directly connected, Serial0/0/0 R [120/1] via , 00:00:25, Serial0/0/0 R /24 [120/1] via , 00:00:25, Serial0/0/0 Ici !

51 Le routeur vérifie la route enfant 172. 16. 3
Le routeur vérifie la route enfant /24 et trouve une correspondance Parent ok Nop /24 The router checks the last child route for /24 and finds a match. The first 24 bits do match. Nop ICI Il faut 24 bits en commun

52 Et si le routeur ne trouve pas une route
Dans ce scénario, il jette le paquet R1# show ip route /24 is subnetted, 3 subnets C is directly connected, FastEthernet0/0 C is directly connected, Serial0/0/0 R [120/1] via , 00:00:25, Serial0/0/0 R /24 [120/1] via , 00:00:25, Serial0/0/0 Parent ok Nop Nop Nop If this child route did not have an exit interface and only included a next-hop IP address, the next-hop IP address would need to be resolved to an exit interface. The lookup process would need to start from the beginning, this time searching the routing table for the nexthop IP address. What happens if the router does not have a route? In this scenario, it discards the packet.

53 Exemple : Processus de routage avec VLSM

54 Exemple : Processus de routage avec VLSM
Destination du paquet : L’utilisation de VSLM ne modifie pas le processus de routage La seule différence est que les routes enfant affichent leurs propres masques RouterX# show ip route /16 is variably subnetted, 3 subnets, 2 masks C /30 is directly connected, Serial0/0/0 C /30 is directly connected, Serial0/0/1 C /24 is directly connected, FastEthernet0/0 Match Parent Packet’s destination IP Address: Using VSLM does not change the lookup process. The only difference with VLSM is that child routes display their own specific subnet masks. 16 bits match the parent route, For there to be a match with the child route, a minimum of 30 leftmost bits must match because the subnet mask is /30 Match child

55 Comportement de routage

56 Comportement de routage classful et classless
Que arrive-t-il s’il y a une correspondance avec une route parent niveau 1, mais aucune correspondance avec le routes enfant niveau 2 ? R2# show ip route /24 is subnetted, 3 subnets R [120/1] via , 00:00:00, Serial0/0/0 C is directly connected, Serial0/0/0 C is directly connected, FastEthernet0/0 C /24 is directly connected, Serial0/0/1 S* /0 is directly connected, Serial0/0/1 Parent ok Nop What happens when there is a match between the packet’s destination IP address and a level 1 parent route, but there is not a match with any of the level 2 child routes? We might assume the routing table lookup process continues looking for a less-specific match in the routing table. However, you will see that this might or might not be the case depending on the configuration of the router. Nop Nop Et alors?

57 Comportement de routage classful et classless
Avoir un comportement classful ou classless n’est pas la même chose qu’être un protocole classful ou classless Pas si vrai, les protocoles classless forcent le comportement classless Être un protocole classful ou classless affecte comment la table sera remplie Avoir un comportement classful ou classless détermine comment chercher dans la table de routage Classless and classful routing behaviors are not the same as classless and classful routing protocols. Classful and classless routing protocols affect how the routing table is populated. Classful and classless routing behaviors determine how the routing table is searched after it is populated.

58 Encore une topologie Lrs protocoles classful comme RIPv1 ne supportent pas les réseaux non contigus Cela n’empêche pas qu’on force son fonctionnement grâce à des routes statiques Classful routing protocols such as RIPv1 do not support discontiguous networks. Even though our current topology has discontiguous networks, we can configure static routes to reach those networks.

59 Encore une topologie R2(config)# ip route 0.0.0.0 0.0.0.0 s0/0/1
R2(config)# router rip R2(config-router)# default-information originate R2(config-router)# no network R2(config-router)# end R2# show ip route /24 is subnetted, 3 subnets R [120/1] via , 00:00:00, Serial0/0/0 C is directly connected, Serial0/0/0 C is directly connected, FastEthernet0/0 C /24 is directly connected, Serial0/0/1 S* /0 is directly connected, Serial0/0/1

60 Encore une topologie On voit que la route statique pour le même réseau devient une route enfant dans la table de routage R3(config)# ip route s0/0/1 R3(config)# no router rip R3(config-router)# end R3# show ip route /16 is variably subnetted, 2 subnets, 2 masks C /24 is directly connected, FastEthernet0/0 S /16 is directly connected, Serial0/0/1 C /24 is directly connected, Serial0/0/1 Notice that the static route for the same network as the parent route is a child route in the routing table. This is because there is a child route for that parent. If there wasn’t a /24 child route, then this /16 static route would be a level 1 ultimate route.

61 Comportement classful : no ip classless
Avant l’ IOS 11.3, no ip classless était le comportement par défaut La commande no ip classless indique au routeur qu’il faut utiliser la recherche selon le comportement classful Match Parent R2# show ip route /24 is subnetted, 3 subnets R [120/1] via , 00:00:00, Serial0/0/0 C is directly connected, Serial0/0/0 C is directly connected, FastEthernet0/0 C /24 is directly connected, Serial0/0/1 S* /0 is directly connected, Serial0/0/1 No match No match No match What happens when there is a match with a parent, but none of the child routes match? Before Cisco IOS Software Release 11.3, no ip classless was the default behavior for Cisco routers. The command no ip classless means that the route lookup process uses classful routing table lookups by default. Et alors ? R1(config)# no ip classless R2(config)# no ip classless R3(config)# no ip classless

62 Comportement classful : no ip classless
Comportement classful : no ip classless Et maintenant ? On a un paquet qui arrive en direction de Le routeur R2 jette le paquet La route par défaut n’est jamais atteinte et utilisée !!!! R2# show ip route /24 is subnetted, 3 subnets R [120/1] via , 00:00:00, Serial0/0/0 C is directly connected, Serial0/0/0 C is directly connected, FastEthernet0/0 C /24 is directly connected, Serial0/0/1 S* /0 is directly connected, Serial0/0/1 Match Parent No match No match So, what happens next? Router R2 drops the packet. Default route is never checked or used. Why does classful routing behavior perform like this? The general idea of classful routing behavior comes from the time when all networks were of a classful nature. At the beginning of the Internet’s growth, an organization received a Class A, Class B, or Class C major network address. When an organization had a classful IP major network address, that organization would also administer all the subnets for that classful address. All routers belonging to the organization would know about all the subnets for the major network. If a subnet was not in the routing table, the subnet did not exist No match Et alors? Jeter le paquet

63 Comportement classful : no ip classless
Comportement classful : no ip classless So, what happens next? Router R2 drops the packet. Default route is never checked or used. Why does classful routing behavior perform like this? The general idea of classful routing behavior comes from the time when all networks were of a classful nature. At the beginning of the Internet’s growth, an organization received a Class A, Class B, or Class C major network address. When an organization had a classful IP major network address, that organization would also administer all the subnets for that classful address. All routers belonging to the organization would know about all the subnets for the major network. If a subnet was not in the routing table, the subnet did not exist

64 Comportement classless : ip classless
Comportement classless : ip classless R2 reçoit un paquet destiné à PC3 ( ) Remember: R2 receives a packet destined for PC3 at

65 Comportement classless : ip classless
Comportement classless : ip classless R2# show ip route /24 is subnetted, 3 subnets R [120/1] via , 00:00:00, Serial0/0/0 C is directly connected, Serial0/0/0 C is directly connected, FastEthernet0/0 C /24 is directly connected, Serial0/0/1 S* /0 is directly connected, Serial0/0/1 Match Parent No match No match No match Now what? Cisco IOS 11.3, Cisco changed the default routing behavior from classful to classless. ip classless command is configured by default. Classless routing behavior means that the routing process no longer assumes that all subnets for a major classful network can be reached only within the child routes of the parent. Classless routing behavior works well for discontiguous networks and classless interdomain routing (CIDR) supernets. R1(config)# ip classless R2(config)# ip classless R3(config)# ip classless

66 Comportement classless : ip classless
Comportement classless : ip classless R2# show ip route /24 is subnetted, 3 subnets R [120/1] via , 00:00:00, Serial0/0/0 C is directly connected, Serial0/0/0 C is directly connected, FastEthernet0/0 C /24 is directly connected, Serial0/0/1 S* /0 is directly connected, Serial0/0/1 Match Parent No match No match No match Now what? Continue searching level 1 supernet routes. The default route is a match, so I is used to forward the packet. Le routeur continue la recherche des routes parent niveau 1. La route par défaut correspond, alors on l’utilise pour transférer le paquet