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New Member

Secondary address

I work for a small ISP. Currently, the fastethernet interface of my 7206 router has 8 secondary addresses assigned to it. One for each /24 I route. I am running OSPF inside and BGP outside. Is there an alternative to this method? Any drawbacks?


Re: Secondary address

The largest draw back I can think of is that with all 8 /24's on one interface I assume that all the hosts on these networks are in one broadcase domain. With no separation at Layer 2 between these hosts broadcase from network 1 are heard, and might be unwanted, from network 2-8. VLAN segmentation in your switching environment will achieve Layer 2 segmentation, lessoning the Broadcast Domain size and increasing performance. Either multiple router interfaces or trunking will give you the L3 separation.

Hope this helps,


New Member

Re: Secondary address

Well, I am not sure how OSPF will react for secondary IP address on the ethernet. Please check

If your router supports trunking, go for subinterfaces.

The only thing that I remember about secondary IPs on an interface is that per to Cisco's recommendation, all routers you have on that same segment has to use a secondary address from the same subnet. I donno why though, but this is what I remember, cause I used to have the same problem.