03-26-2013 05:53 AM - edited 03-07-2019 12:29 PM
I have a Catalyst switch that is redistributing some static routes into OSPF. These are received on a Nexus 7K and appear in the database however the 7K does not add them to its routing table, one of the routes is ignored and not added. I haven't got a clue why this is happening, can anyone please help with this?
The routes on the Catalyst are as follows with ID of 172.30.255.22:
ip route 172.24.59.0 255.255.255.0 10.56.7.46
ip route 192.168.168.0 255.255.255.0 10.56.7.62
on the 7K the database shows:
172.24.59.0 172.30.255.22 1374 0x80001a44 0x1a48 0
192.168.168.0 172.30.255.22 1374 0x80001a45 0x6c5b 0
The routing table shows:
sh ip ro 172.24.59.0/24
IP Route Table for VRF "default"
'*' denotes best ucast next-hop
'**' denotes best mcast next-hop
'[x/y]' denotes [preference/metric]
172.24.59.0/24, ubest/mbest: 1/0
*via 172.30.253.10, Po7, [110/20], 20w4d, ospf-NCC, type-2
sh ip ro 192.168.168.0/24
IP Route Table for VRF "default"
'*' denotes best ucast next-hop
'**' denotes best mcast next-hop
'[x/y]' denotes [preference/metric]
Route not found
Help!!!!!!!!!!!
Solved! Go to Solution.
03-26-2013 07:48 AM
Hello Paul,
the forwarding addresses are actually both learned via an external route
LS age: 2006
Options: 0x20 (No TOS-capability, DC)
LS Type: Type-5 AS-External
Link State ID: 10.56.0.0 (Network address)
Advertising Router: 10.104.7.18
LS Seq Number: 0x80000079
Checksum: 0x96c3
Length: 36
Network Mask: /16
Metric Type: 2 (Larger than any link state path)
TOS: 0
Metric: 20
Forward Address: 0.0.0.0
External Route Tag: 0
in this scenario both external routes SHOULD not be installed in the IP routing table of Nexus node!
To fix this you can on the ASBR node use:
router ospf XX
network 10.56.0.0 0.0.0.255 area YY
passive-interface
in this way you will generate an OSPF internal route for the IP next-hops / forwarding addresses
Hope to help
Giuseppe
03-26-2013 06:49 AM
Hello Paul,
the two routes have different next-hops on the ASBR node.
verify that the forwarding address in the LSA 5 type 2 data structure is reachable via an internal OSPF route.
OSPF does not accept an external route with a forwarding address that is reachable via another external route
Check with
show ip route 10.56.7.62
and look at the contents of the LSA type 5
Hope to help
Giuseppe
03-26-2013 07:06 AM
Giuseppe,
I have attached a log of the output from sh ip ospf data external detail. Could you please look at this and advise.
When looking a the route for 10.56.7.62 I get the below, but I also get this for 10.56.7.46 for the other static route.
Please advise/explain further.
Thanks,
Paul
sh ip ro 10.56.7.62
IP Route Table for VRF "default"
'*' denotes best ucast next-hop
'**' denotes best mcast next-hop
'[x/y]' denotes [preference/metric]
10.56.0.0/16, ubest/mbest: 1/0
*via 172.30.253.10, Po7, [110/20], 2d19h, ospf-NCC, type-2
sh ip ro 10.56.7.46
IP Route Table for VRF "default"
'*' denotes best ucast next-hop
'**' denotes best mcast next-hop
'[x/y]' denotes [preference/metric]
10.56.0.0/16, ubest/mbest: 1/0
*via 172.30.253.10, Po7, [110/20], 2d19h, ospf-NCC, type-2
03-26-2013 07:48 AM
Hello Paul,
the forwarding addresses are actually both learned via an external route
LS age: 2006
Options: 0x20 (No TOS-capability, DC)
LS Type: Type-5 AS-External
Link State ID: 10.56.0.0 (Network address)
Advertising Router: 10.104.7.18
LS Seq Number: 0x80000079
Checksum: 0x96c3
Length: 36
Network Mask: /16
Metric Type: 2 (Larger than any link state path)
TOS: 0
Metric: 20
Forward Address: 0.0.0.0
External Route Tag: 0
in this scenario both external routes SHOULD not be installed in the IP routing table of Nexus node!
To fix this you can on the ASBR node use:
router ospf XX
network 10.56.0.0 0.0.0.255 area YY
passive-interface
in this way you will generate an OSPF internal route for the IP next-hops / forwarding addresses
Hope to help
Giuseppe
03-26-2013 08:48 AM
Guiseppe,
Ok, thanks.
I think I understand. I'm going to do some reconfiguring on the ASBR and will let you know how I get on. Please come back and have a look in about a weeks time. I'll post an update.
Thanks,
Paul
03-27-2013 04:43 AM
Giuseppe, all fixed now
I looked at my ASBR (172.30.255.22) and saw that the link to the target network wasn't configured as a passive interface hence the next hop address of 10.56.7.62 was being advertised into OSPF. This link should be passive because there isn't an OSPF neighbour on that link.
I changed it to be passive and the database on the downstream 7K changed to have 0.0.0.0 as the forwarding address, everything then worked. The 7K placed a route into its routing table and this was passed downstream into the rest of the network.
Many thanks for your help. I've learn't something new.
Paul
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