Cisco – Why would Type-5 AS External OSPF Route not install in routing table

ciscocisco-asrcisco-ios-15ospf

I am redistributing an eBGP route into OSPF, I see the route flooded in the database, but it is not installed in the routing table on the other routers.

What would cause this route not to install in the routing table?

Below is the some troubleshooting output from dallas and atlanta. I'm expecting the route 172.16.192.0/19 to be available on atlanta.

asr1k/dallas#show run | sec router ospf 1

router ospf 1 vrf blue
 router-id 172.18.255.1
 ispf
 prefix-suppression
 timers throttle spf 10 100 1000
 timers throttle lsa 10 100 1000
 timers lsa arrival 50
 timers pacing flood 5
 timers pacing retransmission 60
 redistribute static subnets
 redistribute bgp 65001 subnets tag 0
 passive-interface default
 no passive-interface GigabitEthernet0/0/2.100
 no passive-interface Tunnel1000
 network 172.16.0.0 0.15.255.255 area 0
 neighbor 172.16.254.25
 neighbor 172.16.254.19
 neighbor 172.16.254.22
 neighbor 172.16.254.20
 neighbor 172.16.255.27 cost 5000
 maximum-paths 1

asr1k/dallas#show ip route vrf blue 172.16.192.0

Routing Table: blue
Routing entry for 172.16.192.0/19
  Known via "bgp 65001", distance 20, metric 100
  Tag 65000, type external
  Redistributing via ospf 1
  Advertised by ospf 1 subnets tag 0
  Last update from 169.254.13.109 03:37:09 ago
  Routing Descriptor Blocks:
  * 169.254.13.109, from 169.254.13.109, 03:37:09 ago
      Route metric is 100, traffic share count is 1
      AS Hops 2
      Route tag 65000
      MPLS label: none
      MPLS Flags: NSF

asr1k/dallas#show ip ospf 1 database

            OSPF Router with ID (172.18.255.1) (Process ID 1)

        Router Link States (Area 0)

Link ID         ADV Router      Age         Seq#       Checksum Link count
172.16.255.28   172.16.255.28   358         0x80005070 0x00C976 18
172.17.255.1    172.17.255.1    696         0x8000A4AB 0x003027 18
172.18.255.1    172.18.255.1    344         0x8002933B 0x00B226 23
172.19.255.1    172.19.255.1    1562        0x8000FEE0 0x00553C 22
172.20.255.1    172.20.255.1    762         0x800F04F8 0x00A1D6 23
172.21.255.1    172.21.255.1    1223        0x8002CAA2 0x00DFAF 3
172.22.255.1    172.22.255.1    125         0x8000D829 0x00DD6C 23
172.23.255.1    172.23.255.1    192         0x80004AD5 0x00EFB5 19
172.24.255.1    172.24.255.1    306         0x80006A76 0x0005AF 18
172.25.255.1    172.25.255.1    238         0x8000B51E 0x00B20C 23
172.27.255.1    172.27.255.1    159         0x8000588C 0x000254 19
172.30.255.1    172.30.255.1    1693        0x80001EC0 0x00045E 18
172.31.255.1    172.31.255.1    323         0x8000E561 0x004758 16
172.32.255.1    172.32.255.1    655         0x80003F20 0x00A33F 2

        Net Link States (Area 0)

Link ID         ADV Router      Age         Seq#       Checksum
172.16.253.0    172.25.255.1    2011        0x80003F1C 0x00E1E7

        Type-5 AS External Link States

Link ID         ADV Router      Age         Seq#       Checksum Tag
172.16.192.0    172.18.255.1    597         0x80000003 0x008B87 0
172.17.0.0      172.17.255.1    1461        0x800073C6 0x00CF1B 0
172.18.0.0      172.18.255.1    1881        0x8000739C 0x001003 0
172.19.0.0      172.19.255.1    1066        0x8000736F 0x0056E7 0
172.20.0.0      172.20.255.1    762         0x8000731A 0x00ECA4 0
172.22.0.0      172.22.255.1    1412        0x80007396 0x00CB45 0
172.23.0.0      172.23.255.1    1445        0x80003B75 0x00A2C5 0
172.24.0.0      172.24.255.1    306         0x800052F9 0x00408A 0
172.25.0.0      172.25.255.1    2011        0x80007341 0x003A26 0
172.27.0.0      172.27.255.1    1672        0x80003390 0x003419 0
172.28.0.0      172.16.255.28   601         0x8000442E 0x006F1E 0

And here is the output from a different router:

asr1k/atlanta#show run | sec router ospf 1

router ospf 1 vrf blue
 router-id 172.22.255.1
 ispf
 prefix-suppression
 timers throttle spf 10 100 1000
 timers throttle lsa 10 100 1000
 timers lsa arrival 50
 timers pacing flood 5
 timers pacing retransmission 60
 redistribute static subnets
 passive-interface default
 no passive-interface GigabitEthernet0/0/2.100
 no passive-interface Tunnel1000
 network 172.16.0.0 0.15.255.255 area 0
 neighbor 172.16.254.19
 neighbor 172.16.254.18
 neighbor 172.16.254.25
 neighbor 172.16.254.20
 neighbor 172.16.255.27 cost 5000
 maximum-paths 1

asr1k/atlanta#show ip route vrf blue 172.16.192.0

Routing Table: blue
% Subnet not in table

asr1k/atlanta#show ip ospf 1 database

            OSPF Router with ID (172.22.255.1) (Process ID 1)

        Router Link States (Area 0)

Link ID         ADV Router      Age         Seq#       Checksum Link count
172.16.255.28   172.16.255.28   515         0x80005070 0x00C976 18
172.17.255.1    172.17.255.1    853         0x8000A4AB 0x003027 18
172.18.255.1    172.18.255.1    501         0x8002933B 0x00B226 23
172.19.255.1    172.19.255.1    1718        0x8000FEE0 0x00553C 22
172.20.255.1    172.20.255.1    918         0x800F04F8 0x00A1D6 23
172.21.255.1    172.21.255.1    1380        0x8002CAA2 0x00DFAF 3
172.22.255.1    172.22.255.1    280         0x8000D829 0x00DD6C 23
172.23.255.1    172.23.255.1    347         0x80004AD5 0x00EFB5 19
172.24.255.1    172.24.255.1    462         0x80006A76 0x0005AF 18
172.25.255.1    172.25.255.1    394         0x8000B51E 0x00B20C 23
172.27.255.1    172.27.255.1    314         0x8000588C 0x000254 19
172.30.255.1    172.30.255.1    1849        0x80001EC0 0x00045E 18
172.31.255.1    172.31.255.1    480         0x8000E561 0x004758 16
172.32.255.1    172.32.255.1    811         0x80003F20 0x00A33F 2

        Net Link States (Area 0)

Link ID         ADV Router      Age         Seq#       Checksum
172.16.253.0    172.25.255.1    132         0x80003F1D 0x00DFE8

        Type-5 AS External Link States

Link ID         ADV Router      Age         Seq#       Checksum Tag
172.16.192.0    172.18.255.1    755         0x80000003 0x008B87 0
172.17.0.0      172.17.255.1    1619        0x800073C6 0x00CF1B 0
172.18.0.0      172.18.255.1    1           0x8000739D 0x000E04 0
172.19.0.0      172.19.255.1    1223        0x8000736F 0x0056E7 0
172.20.0.0      172.20.255.1    919         0x8000731A 0x00ECA4 0
172.22.0.0      172.22.255.1    1568        0x80007396 0x00CB45 0
172.23.0.0      172.23.255.1    1601        0x80003B75 0x00A2C5 0
172.24.0.0      172.24.255.1    463         0x800052F9 0x00408A 0
172.25.0.0      172.25.255.1    132         0x80007342 0x003827 0
172.27.0.0      172.27.255.1    1829        0x80003390 0x003419 0
172.28.0.0      172.16.255.28   759         0x8000442E 0x006F1E 0

asr1k/atlanta#show ip ospf 1 database external 172.16.192.0

            OSPF Router with ID (172.22.255.1) (Process ID 1)

        Type-5 AS External Link States

  LS age: 764
  Options: (No TOS-capability, DC, Downward)
  LS Type: AS External Link
  Link State ID: 172.16.192.0 (External Network Number )
  Advertising Router: 172.18.255.1
  LS Seq Number: 80000003
  Checksum: 0x8B87
  Length: 36
  Network Mask: /19
    Metric Type: 2 (Larger than any link state path)
    MTID: 0
    Metric: 1
    Forward Address: 0.0.0.0
    External Route Tag: 0

EDIT

I also tried removing tag 0 on the redistributing router, I have the same behavior in Atlanta.

asr1k/atlanta#show ip ospf 1 database  external 172.16.192.0

            OSPF Router with ID (172.22.255.1) (Process ID 1)

        Type-5 AS External Link States

  LS age: 23
  Options: (No TOS-capability, DC, Downward)
  LS Type: AS External Link
  Link State ID: 172.16.192.0 (External Network Number )
  Advertising Router: 172.18.255.1
  LS Seq Number: 80000001
  Checksum: 0x9D99
  Length: 36
  Network Mask: /19
    Metric Type: 2 (Larger than any link state path)
    MTID: 0
    Metric: 1
    Forward Address: 0.0.0.0
    External Route Tag: 3489667571

asr1k/atlanta# show ip route vrf blue 172.16.192.0

Routing Table: blue
% Network not in table

Best Answer

capability vrf-lite is missing under router ospf

This article has a good explanation. Essentially, the command tells OSPF to ignore the DN bit and use the LSA in the SPF calculations.

https://supportforums.cisco.com/discussion/12754196/where-configure-capability-vrf-lite-ce-or-pe

Related Solutions

Routing – OSPF and routing table

OSPF is a link state protocol that uses multicast. It sends Link State Advertisements (LSAs) that are flooded.

Every router builds a tree by running SPF where the router itself is the root of the tree. In OSPF we have transit networks and stub networks. Transit networks are networks that are used for transit to reach networks while stub networks are the endpoints or leaves as you described it.

If we are in the same area then the router LSA (type-1) is examined to find the destination. Here is a router-LSA to reach the network of R1 which has a RID of 1.1.1.1.

R2#sh ip ospf data router 1.1.1.1

            OSPF Router with ID (2.2.2.2) (Process ID 1)

                Router Link States (Area 0)

  LS age: 256
  Options: (No TOS-capability, DC)
  LS Type: Router Links
  Link State ID: 1.1.1.1
  Advertising Router: 1.1.1.1
  LS Seq Number: 80000005
  Checksum: 0x4B09
  Length: 60
  Number of Links: 3

    Link connected to: a Stub Network
     (Link ID) Network/subnet number: 1.1.1.1
     (Link Data) Network Mask: 255.255.255.255
      Number of TOS metrics: 0
       TOS 0 Metrics: 1

    Link connected to: a Transit Network
     (Link ID) Designated Router address: 13.13.13.1
     (Link Data) Router Interface address: 13.13.13.1
      Number of TOS metrics: 0
       TOS 0 Metrics: 10

    Link connected to: a Transit Network
     (Link ID) Designated Router address: 12.12.12.2
     (Link Data) Router Interface address: 12.12.12.1
      Number of TOS metrics: 0
       TOS 0 Metrics: 10

R1 has a cost of 1 to this stub network. R2 can reach this network through the 12.12.12.0/24 transit network. So we need to add a cost of 10 which brings the total metric to 11.

R2#sh ip route 1.1.1.1
Routing entry for 1.1.1.1/32
  Known via "ospf 1", distance 110, metric 11, type intra area
  Last update from 12.12.12.1 on FastEthernet0/0, 00:06:49 ago
  Routing Descriptor Blocks:
  * 12.12.12.1, from 1.1.1.1, 00:06:49 ago, via FastEthernet0/0
      Route metric is 11, traffic share count is 1

This is an intra area route. For inter area routes OSPF actually behaves like a distance vector protocol because traffic is sent through the ABR. How can we identify an ABR?

R4#sh ip ospf data router 2.2.2.2

            OSPF Router with ID (4.4.4.4) (Process ID 1)

                Router Link States (Area 1)

  Routing Bit Set on this LSA
  LS age: 573
  Options: (No TOS-capability, DC)
  LS Type: Router Links
  Link State ID: 2.2.2.2
  Advertising Router: 2.2.2.2
  LS Seq Number: 80000002
  Checksum: 0xCCB6
  Length: 36
  **Area Border Router**
  Number of Links: 1

    Link connected to: a Transit Network
     (Link ID) Designated Router address: 24.24.24.2
     (Link Data) Router Interface address: 24.24.24.2
      Number of TOS metrics: 0
       TOS 0 Metrics: 10

The B bit is set in the OSPF header which makes a router an ABR.

This can be seen in a packet capture.

OSPF ABR B bit

To find the metric of an inter area route the metric of the ABR to the destination + the metric of the local route to the ABR is added.

R4#sh ip ospf border-routers 

OSPF Process 1 internal Routing Table

Codes: i - Intra-area route, I - Inter-area route

i 2.2.2.2 [10] via 24.24.24.2, FastEthernet0/0, ABR, Area 1, SPF 4
i 3.3.3.3 [10] via 34.34.34.3, FastEthernet0/1, ABR, Area 1, SPF 4
R4#

Here the cost is 10 to reach the two ABRs. Because the cost was 11 from the ABR to the destination that should mean that R4 has a metric of 21.

R4#sh ip route 1.1.1.1
Routing entry for 1.1.1.1/32
  Known via "ospf 1", distance 110, metric 21, type inter area
  Last update from 24.24.24.2 on FastEthernet0/0, 00:09:37 ago
  Routing Descriptor Blocks:
  * 34.34.34.3, from 3.3.3.3, 00:09:37 ago, via FastEthernet0/1
      Route metric is 21, traffic share count is 1
    24.24.24.2, from 2.2.2.2, 00:09:37 ago, via FastEthernet0/0
      Route metric is 21, traffic share count is 1

Which it is. Because there are two ABRs here with the same cost both routes are installed into the RIB/FIB. If we increase the cost to one ABR then only one entry will be installed.

R4#conf t
Enter configuration commands, one per line.  End with CNTL/Z.
R4(config)#int f0/0
R4(config-if)#ip ospf cost 11
R4(config-if)#^Z
R4#sh ip route 1.1.1.1
Routing entry for 1.1.1.1/32
  Known via "ospf 1", distance 110, metric 21, type inter area
  Last update from 34.34.34.3 on FastEthernet0/1, 00:10:58 ago
  Routing Descriptor Blocks:
  * 34.34.34.3, from 3.3.3.3, 00:10:58 ago, via FastEthernet0/1
      Route metric is 21, traffic share count is 1

There really is no concept of AS in OSPF but you can originate a default route and then the best metric would win. I recommend that you read through RFC 2328 and OSPF: Anatomy of an Internet Routing Protocol if you want more understanding of OSPF.

Cisco – Network not participating in OSPF. Does not appear in the routing table

Your loopback 100 address is 172.168.100.0/24, but your network statement is 172.16.100.0/24, so Loopback 100 is not in the OSPF domain.

Best Answer

Related Solutions

Routing – OSPF and routing table

Cisco – Network not participating in OSPF. Does not appear in the routing table

Related Topic