Difference between Major Network Boundary and Classful Network Boundary

[yuchenglai]

Hello All,

I was wondering how EIGRP auto-summarization works.  I have seen documentation stating that when auto-summary is on, EIGRP will summarize to the classful boundary when passing major network boundaries.

What is the actual definition of a major network boundary? 

For example, would 145.1.11.0/25 &145.1.11.128/25 be considered to be in the same major network or different major networks?  This is a bit confusing because technically 145.x.x.x is within the 128-191.x.x.x range, which I believe is a class B range.  However, because of the /25 mask, I am wanting to say 145.1.11.0/25 & 145.1.11.128/25 are different major networks owing to the fact that their bits for the network portion of the address do not exactly match up for the full 25 bits.

If those networks are different major networks, would the classful boundary be 145.1.0.0/16?

Any insight would help!

Thanks,

David

[Mohamed Sobair]

David,

Eigrp Auto summrization summarizes to a classful boundary when passes through DIFFERENT major Network Boundaries.

Both 145.1.11.0/25 &145.1.11.128/25 

Falls On the SAME Major Network which is a class-B of 145.1.0.0/16, at this point no summarization takes place.

It has to be different major Network Boundary for summarization to take affect.

HTH

Mohamed