Enterasys S series routing - OSPF Cost not as expected

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  • Updated 4 years ago
Our core network consists of Enterasys S series routers, all running firmware 8.12.04.003.

The routers are connected by point-to-point links, which are a mixture of 10Gb and 2Gb links.

They are configured in a single OSPF area.

On each router I have configured the cost manually on the point to point links, using 'ip ospf cost 10' for the 10Gb links, and 'ip ospf cost 50' for the 2Gb links.
I have also used the 'ip ospf network point-to-point' command on all the links between routers.

I would expect to see these costs reflected in the routing table, but I do not.
From
a router with one 10Gb link, and one 2Gb link, I'm seeing the same cost via each link to reach a remote subnet, and equal cost multipath routing even seems to be happening.

When I use 'show ip ospf database router 1.1.1.1', where 1.1.1.1 is a router connected via a 2Gb link, with configured cost of 50, I get the following:

Link connected to: point-to-point
     (Link ID) Neighboring Router ID: 5.5.5.5
     (Link Data) Router Interface Address: 192.168.90.17
     Number of TOS metrics: 0
     TOS 0 metric: 10

I have the same topology in GNS3 using Cisco 3700 routers with an identical OSPF configuration and there I get:

      Link connected to: another Router (point-to-point)
     (Link ID) Neighboring Router ID: 5.5.5.5
     (Link Data) Router Interface address: 192.168.90.17
      Number of TOS metrics: 0
       TOS 0 Metrics: 50

Route costs are also as expected, and the 2Gb links are not used to forward traffic.



Can anyone explain why the behaviour differs, or why the configured costs are not respected?
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Jon P

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Posted 4 years ago

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Jon P

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Further to the above -


Interface config on router A:

interface vlan.0.2015

  ip address 192.168.90.17 255.255.255.248 primary

  ip ospf network point-to-point

  ip ospf cost 50

  no shutdown


And on Router B:

interface vlan.0.2015

  ip address 192.168.90.18 255.255.255.248 primary

  ip ospf network point-to-point

  ip ospf cost 50

  no shutdown


So the interface cost should be 50.


But on Router A:


show ip ospf interface vlan.0.2015


vlan.0.2015 is up

  Internet Address 192.168.90.17, Mask 255.255.255.248, Area 0.0.0.0

  Process Id 1,  Router Id 1.1.1.1, Network Type POINT-TO-POINT, Cost: 10

  Transmit Delay is 1 sec, State POINT-TO-POINT, Priority 1

  No designated router on this network

  No backup designated router on this network

  Timer intervals configured: Hello 10, Dead 40, Wait 40, Retransmit 5

  Neighbor Count is 1, Adjacent neighbor count is 1



And on Router B:


show ip ospf interface vlan.0.2015


vlan.0.2015 is up

  Internet Address 192.168.90.18, Mask 255.255.255.248, Area 0.0.0.0

 Process Id 1,  Router Id 5.5.5.5, Network Type POINT-TO-POINT, Cost: 10

  Transmit Delay is 1 sec, State POINT-TO-POINT, Priority 1

  No designated router on this network

  No backup designated router on this network

  Timer intervals configured: Hello 10, Dead 40, Wait 40, Retransmit 5

  Neighbor Count is 1, Adjacent neighbor count is 1


Again, when I build the same topology in GNS3 with Cisco routers the cost is 50 as expected.


Why is the cost 10 rather than 50?