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Problem with two ospf processes on ME-3600x

                 Hi , I have a problem with ME-3600x running two ospf processes. Proc1 is WAN and PRoc2 is LAN. I am redistributing routes into both directions. After a WAN outage ,  certain wan routes did not get redistributed into the LAN process. I had to do a clear ip route to fix the problem. Has anynoe seen such a scenario with ME-3600x or any other switch/router - thanks 

8 REPLIES

Re: Problem with two ospf processes on ME-3600x

Stephen,

My understanding is that clear ip route is only repopulating the routing table from the routing databases from the processes that are running on the device. Have you checked bugs to see if any exist for the ios version that you have? I don't suspect it's a problem with ospf, otherwise I would think you would have needed to clear the ospf process.

HTH,

John

HTH, John *** Please rate all useful posts ***
Hall of Fame Super Silver

Re: Problem with two ospf processes on ME-3600x

Hello Stephen,

multiple OSPF routing processes are executed with a "ships in the night" model: both routing processes are in competition to propose IP prefixes to populate the IP routing table.

The most important aspect is that OSPF type of route is not compared between different routing processes.

Within a single OSPF process OSPF internal route are preferred over OSPF inter area route then are preferred OSPF exernal type 1 over OSPF external type 2.

This information is lost when the comparison is performed in the IP routing table by the IP routing table manager process.

So the risk is that an OSPF external route in process 2 that was originated by redistribution of OSPF process 1 into process 2 is selected and placed in the IP routing table instead of the original route ( that was internal to process 1)

The recommended best practice to have a deterministic behaviour is to use the distance OSPF command to differentiate the Administrative distance for the different type of OSPF routes in both routing processes building a clear hierarchy.

The clear ip route gives a chance for competition between the OSPF processes

see

http://www.cisco.com/en/US/tech/tk365/technologies_white_paper09186a0080531fd2.shtml#singlered

What you can do is something like this

router ospf 1

distance ospf external 120

router ospf 2

distance ospf external 130

Where ospf 1 is the core protocol (WAN side) and ospf 2 is the edge protocol.

This is specially useful when multiple points of mutual redistribution exist in the network.

With a configuration like this you get a deterministic behaviour with each OSPF process that is able to install its own internal routes and with a clear preference of OSPF process 1 external routes over OSPF 2 external routes.

the distance ospf command allows also to modify the cost of internal OSPF routes and of OSPF inter-area routes if needed.

Hope to help

Giuseppe

Re: Problem with two ospf processes on ME-3600x

The clear ip route gives a chance for competition between the OSPF processes

So, that's why that worked Great post Giuseppe!

HTH, John *** Please rate all useful posts ***
Community Member

Re: Problem with two ospf processes on ME-3600x

Thanks John for getting back so quickly

Community Member

Re: Problem with two ospf processes on ME-3600x

THanks a million Giuseppe

I think your explanation is what i was seeing for certain routes. OSPF1 WAN routes were being seen from LAN ospf 2 originating from router#2. Router#2 was getting the WAN routes from Router#1 via OSPF1 WAN process thus a loop occurred

Do you think this shall fix it. Setting all ospf 2 prefixes to distance 200 in ospf1 and vice versa. I have two routers involved so presume i do the same on both

#Router 1

router ospf 1

redist ospf 2 metric 1 metric-type 1 subnets route-map BP2LAN

distance 200 0.0.0.0 255.255.255.255 2

!

router ospf 2

redist ospf 1 metric 1 metric-type 1 subnets route-map WAN

distance 200 0.0.0.0 255.255.255.255 1

default-information originate metric 1 metric-type 1

#Router 2

router ospf 1

redist ospf 2 metric  1 metric-type 1 subnets route-map BP2LAN

distance 200 0.0.0.0 255.255.255.255 2

!

router ospf 2

redist ospf 1 metric 1 metric-type 1 subnets route-map WAN

distance 200 0.0.0.0 255.255.255.255 1

thanks

Hall of Fame Super Silver

Problem with two ospf processes on ME-3600x

Hello Stephen,

I have used the distance ospf approach and in other cases route tags.

the configuration that you have reported is present in the document that I have linked, it should work but it requires that you write in access-list 1 and access-list 2 what are the IP prefixes expected in each OSPF routing domain.

Hope to help

Giuseppe

Community Member

Problem with two ospf processes on ME-3600x

Hi Giuseppe

I am using a definitive  ip prefix-list in the route-maps. Example

ip prefix-list WANsubnets 10.71.0.0/18

!

ip prefix-list BP2subnets 10.231.176.0/24

!

route-map WAN

match ip prefix-list WANsubnets

!

route-map BP2LAN

match ip prefix-list BP2subnets

I have default-originate added to OSPF PROC 2. How does the admin distance command treat this ? One of the problems was that the default route was being seen from LAN proc 2 instead of WAN Proc 1

thanks

Hall of Fame Super Silver

Problem with two ospf processes on ME-3600x

Hello Stephen,

a default route is just an external route in OSPF the only difference is that you cannot redistribute it between processes.

The suggestion is that if you have AD 120 for external routes of OSPF proc 1 (WAN) and AD 130 for external routes of OSPF process 2 ( LAN) the right core facing default route is installed in the IP routing table of both ASBR routers.

We used the distance ospf approach and it worked for us including default routes.

Hope to help

Giuseppe

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