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2010年3月アーカイブの最新記事

MPLS-VPNのトラブル その1 【CCIEレベル】

（所属カテゴリー：IPルーティング | シスコ---投稿日時：2010年3月12日）

ネットワーク構成

下記のネットワーク構成で、MPLS-VPNを通じてR4とR5間の通信ができるようにしたいと考えています。

図 MPLS-VPN ネットワーク構成

ルータの役割は、次の通りです。

PEルータ:R1、R3
Pルータ :R2
CEルータ:R4、R5

PEルータであるR1、R3ではともにVRFとして次のように定義します。

VRF名:VPN
RD:100:100
Import RT:100:100
Export RT:100:100

設定概要

各ルータで行われているMPLS-VPNでの通信に関連する設定は次の通りです。

R1
━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━
ip vrf VPN
 rd 100:100
 route-target export 100:100
 route-target import 100:100
!
interface Loopback0
 ip address 192.168.0.1 255.255.255.255
!
interface FastEthernet0/0
 ip vrf forwarding VPN
 ip address 10.14.14.1 255.255.255.0
!
interface Serial1/0
 ip address 192.168.12.1 255.255.255.0
 encapsulation ppp
 mpls ip
 no peer neighbor-route
!
router ospf 14 vrf VPN
 log-adjacency-changes
 redistribute bgp 100 subnets
 network 10.14.14.1 0.0.0.0 area 0
!
router ospf 1
 log-adjacency-changes
 network 192.168.0.0 0.0.255.255 area 0
!
router bgp 100
 no synchronization
 bgp log-neighbor-changes
 neighbor 192.168.0.3 remote-as 100
 neighbor 192.168.0.3 update-source Loopback0
 no auto-summary
 !
 address-family vpnv4
  neighbor 192.168.0.3 activate
  neighbor 192.168.0.3 send-community extended
 exit-address-family
 !
 address-family ipv4 vrf VPN
  redistribute ospf 14 vrf VPN
  no synchronization
 exit-address-family
━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

R2
━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━
interface Loopback0
 ip address 192.168.0.2 255.255.255.255
!
interface Serial1/0
 ip address 192.168.12.2 255.255.255.0
 encapsulation ppp
 no peer neighbor-route
!
interface Serial1/1
 ip address 192.168.23.2 255.255.255.0
 encapsulation ppp
 mpls ip
 no peer neighbor-route
!
router ospf 1
 log-adjacency-changes
 network 192.168.0.0 0.0.255.255 area 0
━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

R3
━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━
ip vrf VPN
 rd 100:100
 route-target export 100:100
 route-target import 100:100
!
interface Loopback0
 ip address 192.168.0.3 255.255.255.255
!
interface FastEthernet0/0
 ip vrf forwarding VPN
 ip address 10.35.35.3 255.255.255.0
 duplex auto
 speed auto
!
interface Serial1/0
 ip address 192.168.23.3 255.255.255.0
 encapsulation ppp
 mpls ip
 no peer neighbor-route
!
router ospf 35 vrf VPN
 log-adjacency-changes
 redistribute bgp 100 subnets
 network 10.35.35.3 0.0.0.0 area 0
!
router ospf 1
 log-adjacency-changes
 network 192.168.0.0 0.0.255.255 area 0
!
router bgp 100
 no synchronization
 bgp log-neighbor-changes
 neighbor 192.168.0.1 remote-as 100
 neighbor 192.168.0.1 update-source Loopback0
 no auto-summary
 !
 address-family vpnv4
  neighbor 192.168.0.1 activate
  neighbor 192.168.0.1 send-community extended
 exit-address-family
 !
 address-family ipv4 vrf VPN
  redistribute ospf 35 vrf VPN
  no synchronization
 exit-address-family
━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

R4
━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━
interface Loopback0
 ip address 172.16.4.4 255.255.255.0
 ip ospf network point-to-point
!
interface FastEthernet0/0
 ip address 10.14.14.4 255.255.255.0
!
router ospf 1
 log-adjacency-changes
 network 10.14.14.4 0.0.0.0 area 0
 network 172.16.4.4 0.0.0.0 area 0
━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

R5
━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━
interface Loopback0
 ip address 172.16.5.5 255.255.255.0
 ip ospf network point-to-point
!
interface FastEthernet0/0
 ip address 10.35.35.5 255.255.255.0
!
router ospf 1
 log-adjacency-changes
 network 10.35.35.5 0.0.0.0 area 0
 network 172.16.5.5 0.0.0.0 area 0
━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

トラブルの症状

R4、R5のルーティングテーブルを見ると、お互いのルートを確認できます。

R4 show ip route
━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━
R4#show ip route
～省略～

Gateway of last resort is not set

     172.16.0.0/24 is subnetted, 2 subnets
C       172.16.4.0 is directly connected, Loopback0
O E2    172.16.5.0 [110/2] via 10.14.14.1, 00:20:00, FastEthernet0/0
     10.0.0.0/24 is subnetted, 2 subnets
O E2    10.35.35.0 [110/1] via 10.14.14.1, 00:20:00, FastEthernet0/0
C       10.14.14.0 is directly connected, FastEthernet0/0
━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

R5 show ip route
━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━
R5#show ip route
～省略～

Gateway of last resort is not set

     172.16.0.0/24 is subnetted, 2 subnets
O E2    172.16.4.0 [110/2] via 10.35.35.3, 00:23:01, FastEthernet0/0
C       172.16.5.0 is directly connected, Loopback0
     10.0.0.0/24 is subnetted, 2 subnets
C       10.35.35.0 is directly connected, FastEthernet0/0
O E2    10.14.14.0 [110/1] via 10.35.35.3, 00:23:01, FastEthernet0/0
━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

ところが、実際には通信ができません。R4から172.16.5.5へPingすると失敗します。

R4から172.16.5.5へPing
━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━
R4#ping 172.16.5.5 source loopback 0

Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 172.16.5.5, timeout is 2 seconds:
Packet sent with a source address of 172.16.4.4
.....
Success rate is 0 percent (0/5)
━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

CEルータであるR4、R5でお互いのルートが確認できているので、R4とR5には設定ミスがないことが明らかです。そこで、MPLS-VPNバックボーンを構成するR1、R2、R3でそれぞれ次のshowコマンドで原因の切り分けを行いました。

R1
show mpls interface
show mpls ldp neighbor
show ip bgp summary
show ip bgp vpnv4 all
show ip route vrf VPN
show ip cef vrf VPN 172.16.5.0

R2
show mpls interface
show mpls ldp neighbor
show mpls forwarding-table

R3
show mpls interface
show mpls ldp neighbor
show ip bgp summary
show ip bgp vpnv4 all
show ip route vrf VPN
show ip cef vrf VPN 172.16.4.0

R1 showコマンドの結果
━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━
R1#show mpls interface
Interface              IP            Tunnel   Operational
Serial1/0              Yes (ldp)     No       Yes
R1#show mpls ldp neighbor

R1#show ip bgp summary
BGP router identifier 192.168.0.1, local AS number 100
BGP table version is 1, main routing table version 1

Neighbor        V    AS MsgRcvd MsgSent   TblVer  InQ OutQ Up/Down  State/PfxRcd
192.168.0.3     4   100      43      43        1    0    0 00:33:52        0
R1#show ip bgp vpnv4 all
BGP table version is 9, local router ID is 192.168.0.1
Status codes: s suppressed, d damped, h history, * valid, > best, i - internal,
              r RIB-failure, S Stale
Origin codes: i - IGP, e - EGP, ? - incomplete

   Network          Next Hop            Metric LocPrf Weight Path
Route Distinguisher: 100:100 (default for vrf VPN)
*> 10.14.14.0/24    0.0.0.0                  0         32768 ?
*>i10.35.35.0/24    192.168.0.3              0    100      0 ?
*> 172.16.4.0/24    10.14.14.4               2         32768 ?
*>i172.16.5.0/24    192.168.0.3              2    100      0 ?
R1#show ip route vrf VPN

Routing Table: VPN
Codes: 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
       i - IS-IS, su - IS-IS summary, 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

     172.16.0.0/24 is subnetted, 2 subnets
O       172.16.4.0 [110/2] via 10.14.14.4, 00:35:16, FastEthernet0/0
B       172.16.5.0 [200/2] via 192.168.0.3, 00:33:31
     10.0.0.0/24 is subnetted, 2 subnets
B       10.35.35.0 [200/0] via 192.168.0.3, 00:33:31
C       10.14.14.0 is directly connected, FastEthernet0/0
R1#show ip cef vrf VPN 172.16.5.0
172.16.5.0/24, version 14, epoch 0, cached adjacency to Serial1/0
0 packets, 0 bytes
  tag information set
    local tag: VPN-route-head
    fast tag rewrite with
        Recursive rewrite via 192.168.0.3/32, tags imposed {21}
  via 192.168.0.3, 0 dependencies, recursive
    next hop 192.168.12.2, Serial1/0 via 192.168.0.3/32
    valid cached adjacency
    tag rewrite with
        Recursive rewrite via 192.168.0.3/32, tags imposed {21}
━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

R2 showコマンドの結果
━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━
R2#show mpls interface
Interface              IP            Tunnel   Operational
Serial1/1              Yes (ldp)     No       Yes
R2#show mpls ldp neighbor
    Peer LDP Ident: 192.168.0.3:0; Local LDP Ident 192.168.0.2:0
        TCP connection: 192.168.0.3.48691 - 192.168.0.2.646
        State: Oper; Msgs sent/rcvd: 89/90; Downstream
        Up time: 01:12:09
        LDP discovery sources:
          Serial1/1, Src IP addr: 192.168.23.3
        Addresses bound to peer LDP Ident:
          192.168.23.3    192.168.0.3
R2#show mpls forwarding-table
Local  Outgoing    Prefix            Bytes tag  Outgoing   Next Hop
tag    tag or VC   or Tunnel Id      switched   interface
16     Untagged    192.168.0.1/32    3317       Se1/0      point2point
17     Pop tag     192.168.0.3/32    2809       Se1/1      point2point
━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

R3 showコマンドの結果
━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━
R3#show mpls interface
Interface              IP            Tunnel   Operational
Serial1/0              Yes (ldp)     No       Yes
R3#show mpls ldp neighbor
    Peer LDP Ident: 192.168.0.2:0; Local LDP Ident 192.168.0.3:0
        TCP connection: 192.168.0.2.646 - 192.168.0.3.48691
        State: Oper; Msgs sent/rcvd: 90/90; Downstream
        Up time: 01:12:51
        LDP discovery sources:
          Serial1/0, Src IP addr: 192.168.23.2
        Addresses bound to peer LDP Ident:
          192.168.12.2    192.168.23.2    192.168.0.2
R3#show ip bgp summary
BGP router identifier 192.168.0.3, local AS number 100
BGP table version is 1, main routing table version 1

Neighbor        V    AS MsgRcvd MsgSent   TblVer  InQ OutQ Up/Down  State/PfxRcd
192.168.0.1     4   100      45      45        1    0    0 00:35:25        0
R3#show ip bgp vpnv4 all
BGP table version is 9, local router ID is 192.168.0.3
Status codes: s suppressed, d damped, h history, * valid, > best, i - internal,
              r RIB-failure, S Stale
Origin codes: i - IGP, e - EGP, ? - incomplete

   Network          Next Hop            Metric LocPrf Weight Path
Route Distinguisher: 100:100 (default for vrf VPN)
*>i10.14.14.0/24    192.168.0.1              0    100      0 ?
*> 10.35.35.0/24    0.0.0.0                  0         32768 ?
*>i172.16.4.0/24    192.168.0.1              2    100      0 ?
*> 172.16.5.0/24    10.35.35.5               2         32768 ?
R3#show ip route vrf VPN

Routing Table: VPN
Codes: 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
       i - IS-IS, su - IS-IS summary, 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

     172.16.0.0/24 is subnetted, 2 subnets
B       172.16.4.0 [200/2] via 192.168.0.1, 00:35:09
O       172.16.5.0 [110/2] via 10.35.35.5, 00:36:41, FastEthernet0/0
     10.0.0.0/24 is subnetted, 2 subnets
C       10.35.35.0 is directly connected, FastEthernet0/0
B       10.14.14.0 [200/0] via 192.168.0.1, 00:35:09
R3#show ip cef vrf VPN 172.16.4.0
172.16.4.0/24, version 14, epoch 0, cached adjacency to Serial1/0
0 packets, 0 bytes
  tag information set
    local tag: VPN-route-head
    fast tag rewrite with Se1/0, point2point, tags imposed: {16 22}
  via 192.168.0.1, 0 dependencies, recursive
    next hop 192.168.23.2, Serial1/0 via 192.168.0.1/32
    valid cached adjacency
    tag rewrite with Se1/0, point2point, tags imposed: {16 22}
━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

R1～R3のshowコマンドによって設定ミスがわかったので修正すると、正常にMPLS-VPNを通じてR4-R5間の通信ができるようになりました。

問題

• R4、R5ではお互いのルートを学習できているのになぜ通信できないのですか？
• MPLS-VPN経由でR4-R5間の通信ができるようにするためには、どのように設定を修正すればよいですか？