04-25-2013 08:34 PM - edited 03-03-2019 07:03 AM
OSPF the router ID is assigned base on what?
I remember that it was based on first loopback address.
if there're two loopback address than the first one is picked or the one with the highest IP address get picked?
Also what the point of loopback address for OSPF?
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04-26-2013 04:47 AM
Hello John,
As Matthew said, this is order in which router choose OSPF ID.
1. configured router ID
2. IP of highest up/up loopback
3. IP of highest up/up physical interface
As you know, OSPF is link state routing protocol, it knows entire topology which belongs to same area. This topology is created based on router ID. So router ID for each router has to be stable. You can imagine that if router has to change router ID (physical interface went down) entire topology on all routers has to be rebuilt.
Best Regards
Please rate all helpful posts and close solved questions
04-25-2013 10:30 PM
The router ID is based on the highest IP address configured on the router unless there is a loopback configured. Then it is the highest loopback address.
Physical interfaces can go down though. A logical interface like a loopback is always up. That's why you want your router ID attached to a loopback interface.
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04-26-2013 04:47 AM
Hello John,
As Matthew said, this is order in which router choose OSPF ID.
1. configured router ID
2. IP of highest up/up loopback
3. IP of highest up/up physical interface
As you know, OSPF is link state routing protocol, it knows entire topology which belongs to same area. This topology is created based on router ID. So router ID for each router has to be stable. You can imagine that if router has to change router ID (physical interface went down) entire topology on all routers has to be rebuilt.
Best Regards
Please rate all helpful posts and close solved questions
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