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CCNA試験対策 ch16 Configuring IPv4 Addresses and Static Routes

CCNA ネットワーク 勉強メモ

IP Routing

IPv4 Routing Process Reference

An Example of IP Routing

Host Forwards the IP Packet to the Default Router (Gateway)

  • routing tableにしたがってルータホップする
    1. Decide Whether to Process the Incoming Frame
    2. De-Encapsulation of the IP Packet
    3. Choosing Where to Forward the Packet
    4. Encapsulating the Packet in a New Frame

Configuring IP Addresses and Connected Routes

Connected Routes and the ip address Command

  • 各interfaceに割り当てたIPv4アドレスの確認
Router#show running-config 
Building configuration...

...
!
interface GigabitEthernet0/0/0
 ip address 192.168.1.21 255.255.255.0
 duplex auto
 speed auto
!
interface GigabitEthernet0/0/1
 ip address 192.168.2.21 255.255.255.0
 duplex auto
 speed auto
!
interface GigabitEthernet0/0/2
 no ip address
 duplex auto
 speed auto
 shutdown
!
interface Vlan1
 no ip address
 shutdown
!
...
Router>show ip route 
Codes: L - local, C - connected, S - static, R - RIP, M - mobile, B - BGP
       D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
       N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
       E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
       i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, ia - IS-IS inter area
       * - candidate default, U - per-user static route, o - ODR
       P - periodic downloaded static route

Gateway of last resort is not set

     192.168.1.0/24 is variably subnetted, 2 subnets, 2 masks
C       192.168.1.0/24 is directly connected, GigabitEthernet0/0/0
L       192.168.1.21/32 is directly connected, GigabitEthernet0/0/0
     192.168.2.0/24 is variably subnetted, 2 subnets, 2 masks
C       192.168.2.0/24 is directly connected, GigabitEthernet0/0/1
L       192.168.2.21/32 is directly connected, GigabitEthernet0/0/1

Router>

The ARP Table on a Cisco Router

Router>show ip arp 
Protocol  Address          Age (min)  Hardware Addr   Type   Interface
Internet  192.168.1.11            28  00D0.BC92.ADC9  ARPA   GigabitEthernet0/0/0
Internet  192.168.1.21            -   0002.16D5.8701  ARPA   GigabitEthernet0/0/0
Internet  192.168.2.11            27  0090.2BBE.8756  ARPA   GigabitEthernet0/0/1
Internet  192.168.2.21            -   0002.16D5.8702  ARPA   GigabitEthernet0/0/1

Configuring Static Routes

  • CCNAではstatic routesは4つのトピックに分類される
    • network routes
    • host routes
    • floating static routes
    • default routes

Static Network Routes

f:id:wand_ta:20200504200148p:plain

  • routingが定義されていないので、サブネット越えができない
R1#show ip route static
R1#
  • static routingを設定する
R1#configure terminal 
Enter configuration commands, one per line.  End with CNTL/Z.
R1(config)#ip route 192.168.2.0 255.255.255.0 172.16.1.21
R1(config)#
%SYS-5-CONFIG_I: Configured from console by console

R1(config)#
R1(config)#end
R1#
R1#
R1#show ip route static 
S    192.168.2.0/24 [1/0] via 172.16.1.21

R1#
R2#configure
Configuring from terminal, memory, or network [terminal]? 
Enter configuration commands, one per line.  End with CNTL/Z.
R2(config)#
R2(config)#
R2(config)#ip route 192.168.1.0 255.255.255.0 172.16.1.11
R2(config)#
R2(config)#end
R2#show ip route st
R2#show ip route static 
S    192.168.1.0/24 [1/0] via 172.16.1.11
  • サブネット越えできるようになる
C:\>ping 192.168.2.11

Pinging 192.168.2.11 with 32 bytes of data:

Reply from 192.168.2.11: bytes=32 time=1ms TTL=126
Reply from 192.168.2.11: bytes=32 time=1ms TTL=126
Reply from 192.168.2.11: bytes=32 time=1ms TTL=126
Reply from 192.168.2.11: bytes=32 time=1ms TTL=126

Ping statistics for 192.168.2.11:
    Packets: Sent = 4, Received = 4, Lost = 0 (0% loss),
Approximate round trip times in milli-seconds:
    Minimum = 1ms, Maximum = 1ms, Average = 1ms
  • ip routeの書式
R1(config)#ip route  ?
  A.B.C.D  Destination prefix
R1(config)#ip route  172.16.1.11 255.255.255.0 ?
  A.B.C.D          Forwarding router's address
  Dialer           Dialer interface
  Ethernet         IEEE 802.3
  FastEthernet     FastEthernet IEEE 802.3
  GigabitEthernet  GigabitEthernet IEEE 802.3z
  Loopback         Loopback interface
  Null             Null interface
  Serial           Serial
  Vlan             Catalyst Vlans
R1(config)#ip route  172.16.1.11 255.255.255.0
  • 第1引数: 宛先サブネット
    • A.B.C.D Destination prefix
  • 第2引数: いろいろ
    • A.B.C.D Forwarding router's address
      • 上で指定したのはこれ
    • interfaceを設定することもできる
R1(config)#ip route 192.168.2.0 255.255.255.0 S0/1/0
%Default route without gateway, if not a point-to-point interface, may impact performance
R1(config)#
R1(config)#
R1(config)#end
R1#
%SYS-5-CONFIG_I: Configured from console by console
show ip route st
R1#show ip route static 
S    192.168.2.0/24 [1/0] via 172.16.1.21
                    is directly connected, Serial0/1/0

R1#

Static Host Routes

ip route 10.1.1.0 255.255.255.0 10.2.2.2
ip route 10.1.1.9 255.255.255.255 10.9.9.9
  • 2つめは1つめと競合している
  • 2つめのほうが詳細なのでこちらが優先される

Floating Static Routes

  • あるstatic routeが別のstatic routeや、routing protocolにより学習されたrouteと競合したら？
    • OSPFとか
  • administrative distance に基づいてどれを使用するか決定される
  • デフォルトでは、static routeがOSPFで学習されたrouteよりも優先
    • staticのadministrative distance: 1
    • OSPFで学習されたroute: 110
R1>show ip route static 
S    192.168.2.0/24 [1/0] via 172.16.1.21
                    is directly connected, Serial0/1/0
R1>show ip route 192.168.2.0
Routing entry for 192.168.2.0/24
Known via "static", distance 1, metric 0 (connected)
  Routing Descriptor Blocks:
  * 172.16.1.21
      Route metric is 0, traffic share count is 1
    directly connected, via Serial0/1/0
      Route metric is 0, traffic share count is 1

R1>
  • administrative distance: 1
Known via "static", distance 1, metric 0 (connected)
  • ip routeコマンドで administrative distanceを指定できる
R1#configure  terminal 
Enter configuration commands, one per line.  End with CNTL/Z.
R1(config)#ip route 192.168.2.0 255.255.255.0 172.16.1.21 130
R1(config)#end
%SYS-5-CONFIG_I: Configured from console by console
R1#show ip route 192.168.2.0
Routing entry for 192.168.2.0/24
Known via "static", distance 130, metric 0 (connected)
  Routing Descriptor Blocks:
  * directly connected, via Serial0/1/0
      Route metric is 0, traffic share count is 1
    172.16.1.21
      Route metric is 0, traffic share count is 1

R1#show ip route static
S    192.168.2.0/24 is directly connected, Serial0/1/0
                    [130/0] via 172.16.1.21

Static Default Routes

R1#configure terminal 
Enter configuration commands, one per line.  End with CNTL/Z.
R1(config)#
R1(config)#
R1(config)#ip route 0.0.0.0 0.0.0.0 s0/1/0
%Default route without gateway, if not a point-to-point interface, may impact performance
R1(config)#end
R1#
%SYS-5-CONFIG_I: Configured from console by console
R1#show ip route
Codes: L - local, C - connected, S - static, R - RIP, M - mobile, B - BGP
       D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
       N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
       E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
       i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, ia - IS-IS inter area
       * - candidate default, U - per-user static route, o - ODR
       P - periodic downloaded static route

Gateway of last resort is 0.0.0.0 to network 0.0.0.0

     172.16.0.0/16 is variably subnetted, 2 subnets, 2 masks
C       172.16.1.0/24 is directly connected, Serial0/1/0
L       172.16.1.11/32 is directly connected, Serial0/1/0
     192.168.1.0/24 is variably subnetted, 2 subnets, 2 masks
C       192.168.1.0/24 is directly connected, GigabitEthernet0/0/0
L       192.168.1.21/32 is directly connected, GigabitEthernet0/0/0
S    192.168.2.0/24 is directly connected, Serial0/1/0
                    [130/0] via 172.16.1.21
S*   0.0.0.0/0 is directly connected, Serial0/1/0

R1#
Gateway of last resort is 0.0.0.0 to network 0.0.0.0
  • 他のどれにもマッチしなければここに送る

Troubleshooting Static Routes

  • routeの設定誤り
  • routeの設定がない
  • 設定は正しいがパケットがとどかない

Troubleshooting Incorrect Static Routes That Appear in the IP Routing Table

The Static Route Dows Not Appear in the IP Routing Table

  • up/up でないとrouting tableに現れなくなる
R1#
%LINK-3-UPDOWN: Interface Serial0/1/0, changed state to down

%LINEPROTO-5-UPDOWN: Line protocol on Interface Serial0/1/0, changed state to down

%LINK-5-CHANGED: Interface Serial0/1/0, changed state to up
show ip route
Codes: L - local, C - connected, S - static, R - RIP, M - mobile, B - BGP
       D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
       N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
       E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
       i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, ia - IS-IS inter area
       * - candidate default, U - per-user static route, o - ODR
       P - periodic downloaded static route

Gateway of last resort is not set

     192.168.1.0/24 is variably subnetted, 2 subnets, 2 masks
C       192.168.1.0/24 is directly connected, GigabitEthernet0/0/0
L       192.168.1.21/32 is directly connected, GigabitEthernet0/0/0
  • up/upでなくても残す場合はpermanentをつけるらしい
    • Packet Tracerでは動作せず
R1(config)#ip route 192.168.2.0 255.255.255.0 s0/1/0 permanent
                                                     ^
% Invalid input detected at '^' marker.

The Correct Static Route Appears but Works Poorly

  • routingは悪くないかも
    • 【所感】end device側のデフォゲ設定忘れとかね

IP Forwarding with the Longest Prefix Match

Using show ip route to Find the Best Route

R1#show ip route static
S    192.168.2.0/24 is directly connected, Serial0/1/0
S*   0.0.0.0/0 is directly connected, Serial0/1/0
  • いちばんマッチする部分が長いrouteが選択される

Using show ip route address to Find the Best Route

R1#show ip route 192.168.2.11
Routing entry for 192.168.2.0/24
Known via "static", distance 1, metric 0 (connected)
  Routing Descriptor Blocks:
  * directly connected, via Serial0/1/0
      Route metric is 0, traffic share count is 1

R1#
  • 指定のアドレスやsubnet宛のパケットがどのrouteで伝送されるか

Interpreting The IP Routing Table

R1#show ip route
Codes: L - local, C - connected, S - static, R - RIP, M - mobile, B - BGP
       D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
       N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
       E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
       i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, ia - IS-IS inter area
       * - candidate default, U - per-user static route, o - ODR
       P - periodic downloaded static route

Gateway of last resort is 0.0.0.0 to network 0.0.0.0

     172.16.0.0/16 is variably subnetted, 2 subnets, 2 masks
C       172.16.1.0/24 is directly connected, Serial0/1/0
L       172.16.1.11/32 is directly connected, Serial0/1/0
     192.168.1.0/24 is variably subnetted, 2 subnets, 2 masks
C       192.168.1.0/24 is directly connected, GigabitEthernet0/0/0
L       192.168.1.21/32 is directly connected, GigabitEthernet0/0/0
S    192.168.2.0/24 is directly connected, Serial0/1/0
                    [130/0] via 172.16.1.21
S*   0.0.0.0/0 is directly connected, Serial0/1/0

R1#
idea value in example description
Classful Network 172.16.0.0/16
# subnets 2 subnets
# masks 2 masks
prefix/prefix length 172.16.1.0/24
administrative distance 130
metric 130/0 の 0
next-hop router via 172.16.1.21 このルータにホップするよ、ってやつ
outgoing interface Serial0/1/0