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Need Advice for EIGRP-OSPF Migration

Hi,

  I'm currently planning an integration of our network from EIGRP to OPSF routing protocol. I attached the topology for better to understand my topology.

My plan is to migrate first the network under R2 and 3750-Core to OSPF then redistribute it to EIGRP. Can someone please verify my configuarations if this are correct or needs some more improvements/correction? Also just want to know on how IP addressing scheme on loopback interafaces will be much better for my design.

cheers!

reymon

4 ACCEPTED SOLUTIONS

Accepted Solutions
VIP Super Bronze

Re: Need Advice for EIGRP-OSPF Migration

Reymon,

You can turn on OSPF in conjunction with your EIGRP.  Since the AD for OSPF is 110 and for EIGRP is 90, EIGRP would still be the preferred routing protocol, this way you can test your OSPF for a week or 2  by making sure your OSPF neighbors are up, your database is maintaning the correct subnets before you completely delete EIGRP.  Also, make sure you have an unused subnet assigned to your Loopback interfaces.

You may want to make your area 70, 71, and 72 NSSA, this way they only use a default route to get to any other area and you don't have to maintain a bigger routing table on your 3560 and 3750s.

Of course make sure you do every thing during an outage.

HTH

Reza

Hall of Fame Super Blue

Re: Need Advice for EIGRP-OSPF Migration

I can't read the visio so this may not be relevant but just an additional note to Reza's post.

EIGRP is 90 AD and OSPF is 110. However if you have any redistributed routes into EIGRP such as static routes for example these will have an AD of 170 and therefore the OSPF routes could take precedence. You can account for this by changing the distance of OSPF to > than 170 while you migrate across.

One other thing worth noting. OSPF can be quite hard on router resources so make sure you do not have any routers/switches that already running a high CPU for example before enabling OSPF.

Jon

Hall of Fame Super Silver

Re: Need Advice for EIGRP-OSPF Migration

Hello Reymon,

actually as suggested by Reza I would consider a different approach:

I would deploy OSPF and EIGRP in parallel.

Then I would compare OSPF database and EIGRP database.

If the contents of the two database are the same set of routes you know that you can start to remove EIGRP process on single nodes.

In other words, there is not a real need for the mutual redistribution you have configured.

Be aware that mutual redistribution in the way you have configured is fine if there is a single router performing mutual redistribution.

if multiple routers will be configured for mutual redistribution you would need to use safety measures like route tags.

Hope to help

Giuseppe

Hall of Fame Super Silver

Re: Need Advice for EIGRP-OSPF Migration

Hello  Reymon,

what Jon has noted is important: the hierarchy of admin distance allows introduction of OSPF routes in parallel but OSPF external routes are preferred to EIGRP external routes (default AD 170 for D EX, 110 for O E1 or O E2).

So for migration this has to be considered you can manipulate OSPF AD per OSPF route type with

router ospf xx

distance ospf {external dist1 | inter-area dist2 | intra-area dist3}

see

http://www.cisco.com/en/US/docs/ios/iproute/command/reference/irp_osp1.html#wp1013195

About how to design the OSPF domain mutiple choices are possible: non zero areas can be made NSSA to leave you the possibility to redistribute routes from other protcols without importing all the OSPF area 0 database (no external LSAs are allowed to go into any form of LSA area).

A stub area or a totally stub area are good for access layer on sites where you choice to use network ... area yy command + passive-interface instead of redistribute connected that is allowed only on NSSA areas.

The suggestion is to avoid to create unnecessary external routes so network ... area yy command + passive-interface  has to be preferred to redistribute connected.

internal routes can be summarized or filtered at area border by ABR nodes this is no possible with external routes.

Internet connectivity:

if multiple internet exit points exist I recommend to generate OSPF default route of type O E1, this provides better control then using O E2 (default type of external routes).

O E1 routes are preferred over O E2 routes and this provides another level of control.

Hope to help

Giuseppe

6 REPLIES
VIP Super Bronze

Re: Need Advice for EIGRP-OSPF Migration

Reymon,

You can turn on OSPF in conjunction with your EIGRP.  Since the AD for OSPF is 110 and for EIGRP is 90, EIGRP would still be the preferred routing protocol, this way you can test your OSPF for a week or 2  by making sure your OSPF neighbors are up, your database is maintaning the correct subnets before you completely delete EIGRP.  Also, make sure you have an unused subnet assigned to your Loopback interfaces.

You may want to make your area 70, 71, and 72 NSSA, this way they only use a default route to get to any other area and you don't have to maintain a bigger routing table on your 3560 and 3750s.

Of course make sure you do every thing during an outage.

HTH

Reza

Hall of Fame Super Blue

Re: Need Advice for EIGRP-OSPF Migration

I can't read the visio so this may not be relevant but just an additional note to Reza's post.

EIGRP is 90 AD and OSPF is 110. However if you have any redistributed routes into EIGRP such as static routes for example these will have an AD of 170 and therefore the OSPF routes could take precedence. You can account for this by changing the distance of OSPF to > than 170 while you migrate across.

One other thing worth noting. OSPF can be quite hard on router resources so make sure you do not have any routers/switches that already running a high CPU for example before enabling OSPF.

Jon

Hall of Fame Super Silver

Re: Need Advice for EIGRP-OSPF Migration

Hello Reymon,

actually as suggested by Reza I would consider a different approach:

I would deploy OSPF and EIGRP in parallel.

Then I would compare OSPF database and EIGRP database.

If the contents of the two database are the same set of routes you know that you can start to remove EIGRP process on single nodes.

In other words, there is not a real need for the mutual redistribution you have configured.

Be aware that mutual redistribution in the way you have configured is fine if there is a single router performing mutual redistribution.

if multiple routers will be configured for mutual redistribution you would need to use safety measures like route tags.

Hope to help

Giuseppe

New Member

Re: Need Advice for EIGRP-OSPF Migration

Hi Guislar,


   Thanks for your reply! So it will be better to deploy ospf and eigrp in parallel. I'm also planning to remove my internet connection on R1, R2 and R3 so I can separate WAN and Internet connection. This is to prepare implementing firewall and not IOS firewall use by router, will this be a good one? Can you suggest if where I can use stub or totally-stub  or nssa in this network because it makes me confuse of taking out internet connection from R1,R2 and R3 as the default route is pointing on them. I attached the new topology.

Thanks,

reymon

Hall of Fame Super Silver

Re: Need Advice for EIGRP-OSPF Migration

Hello  Reymon,

what Jon has noted is important: the hierarchy of admin distance allows introduction of OSPF routes in parallel but OSPF external routes are preferred to EIGRP external routes (default AD 170 for D EX, 110 for O E1 or O E2).

So for migration this has to be considered you can manipulate OSPF AD per OSPF route type with

router ospf xx

distance ospf {external dist1 | inter-area dist2 | intra-area dist3}

see

http://www.cisco.com/en/US/docs/ios/iproute/command/reference/irp_osp1.html#wp1013195

About how to design the OSPF domain mutiple choices are possible: non zero areas can be made NSSA to leave you the possibility to redistribute routes from other protcols without importing all the OSPF area 0 database (no external LSAs are allowed to go into any form of LSA area).

A stub area or a totally stub area are good for access layer on sites where you choice to use network ... area yy command + passive-interface instead of redistribute connected that is allowed only on NSSA areas.

The suggestion is to avoid to create unnecessary external routes so network ... area yy command + passive-interface  has to be preferred to redistribute connected.

internal routes can be summarized or filtered at area border by ABR nodes this is no possible with external routes.

Internet connectivity:

if multiple internet exit points exist I recommend to generate OSPF default route of type O E1, this provides better control then using O E2 (default type of external routes).

O E1 routes are preferred over O E2 routes and this provides another level of control.

Hope to help

Giuseppe

New Member

Re: Need Advice for EIGRP-OSPF Migration

Many thanks! Really help me a lot!

cheers!

reymon

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