From: Hossam Mahmoud (sam6626@yahoo.com)
Date: Tue Apr 22 2003 - 17:06:48 GMT-3
Dear All,
In most of the CCIE lab scenarios we have three routing domains (routing protocols). One is the backbone routing domain and two different edge routing domains. In the shown figure we have OSPF as the core routing domain, while RIP and EIGRP are the edge routing domains.
In some scenarios we need to do mutual redistribution between both the edge routing domains and the core domain. In the shown example we do mutual redistribution on the RIP/OSPF border (R2) and mutual redistribution on the EIGRP/OSPF border (R3).
In all mutual redistribution cases we need a technique to prevent routing loops that shows due to route feedbacks and other sources. I usually use a common technique in all similar cases to prevent these problems.
The technique I use as shown in the attached diagram is:
- Redistribute the backbone domain (OSPF in the shown case) into the first edge domain (RIP in the shown case) on R2 (Red. 21 as shown by the arrow).
- Redistribute the first edge domain (RIP in the shown case) into the backbone domain on R2 (Red. 12 as shown by the arrow) while using a route map that allows only the networks (routes) that I need to reach form the backbone and deny all other networks. In the shown example the route map will allow only the following networks
' Net 11 (Where Net xx stands for any subnet in the network x.x.x.x)
' Net 12
' Net 13
' Net 14
' Deny all
- This filter will prevent loops as it will only pass the required networks.
- Redistribute the backbone domain (OSPF in the shown case) into the second edge domain (EIGRP in the shown case) on R3 (Red. 34 as shown by the arrow).
- Redistribute the second edge domain (EIGRP in the shown case) into the backbone domain on R3 (Red. 43 as shown by the arrow) while using a route map that allows only the networks (routes) that I need to reach form the backbone and deny all other networks. In the shown example the route map will allow only the following networks
' Net 41
' Net 42
' Net 43
' Net 44
' Net 45
' Deny all
- This filter will prevent loops as it will only pass the required networks.
My question now is:
1- Does this technique ensures loop free network?
2- Is there any a consideration or problems related to the above technique?
Or can I use this technique wherever I have mutual redistribution?
Thanks a lot
Hossam
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