Question about BGP Aggregate with AS-SET

Hi Experts,

I have three router in AS 100

R1=Fa0/0-----------------Fa0/0=R2
                |
                |
              Fa0/0
                |
                R3

R1 is getting the route 112.0.0.0/8 to 119.0.0.0/8 from as-path 54 50 60 and advertsie it to R3

R1 SH IP BGP Output:-

*> 112.0.0.0 1.1.1.254 0 0 54 50 60 i
*> 113.0.0.0 1.1.1.254 0 0 54 50 60 i
*> 114.0.0.0 1.1.1.254 0 0 54 i
*> 115.0.0.0 1.1.1.254 0 0 54 i
*> 116.0.0.0 1.1.1.254 0 0 54 i
*> 117.0.0.0 1.1.1.254 0 0 54 i
*> 118.0.0.0 1.1.1.254 0 0 54 i
*> 119.0.0.0 1.1.1.254 0 0 54 i

R3 SH IP BGP Output:-

*>i112.0.0.0 1.1.1.254 0 100 0 54 50 60 i
*>i113.0.0.0 1.1.1.254 0 100 0 54 50 60 i
*>i114.0.0.0 1.1.1.254 0 100 0 54 i
*>i115.0.0.0 1.1.1.254 0 100 0 54 i
*>i116.0.0.0 1.1.1.254 0 100 0 54 i
*>i117.0.0.0 1.1.1.254 0 100 0 54 i
*>i118.0.0.0 1.1.1.254 0 100 0 54 i
*>i119.0.0.0 1.1.1.254 0 100 0 54 i

If try to aggregate above subnets into one prefix on R1 with:-

router bgp 100
aggregate-address 112.0.0.0 248.0.0.0 summary-only as-set

I can see that the router is setting up the AS-SET in BGP table, as per below output:-

s>i112.0.0.0 1.1.1.254 0 100 0 54 50 60 i
*> 112.0.0.0/5 0.0.0.0 100 32768 {54,50,60} i
s>i113.0.0.0 1.1.1.254 0 100 0 54 50 60 i
s>i114.0.0.0 1.1.1.254 0 100 0 54 i
s>i115.0.0.0 1.1.1.254 0 100 0 54 i
s>i116.0.0.0 1.1.1.254 0 100 0 54 i
s>i117.0.0.0 1.1.1.254 0 100 0 54 i
s>i118.0.0.0 1.1.1.254 0 100 0 54 i
s>i119.0.0.0 1.1.1.254 0 100 0 54 i

but instead of aggregating all route,if I try to aggregate 112.0.0.0/8 and 113.0.0.0/8 into on 112.0.0.0/7 prefix, router generate the aggregate prefix in BGP table instead of showing the AS-SET it shows the AS-PATH-SEQ on aggregated prefix.

router bgp 100
aggregate-address 112.0.0.0 254.0.0.0 summary-only as-set

s>i112.0.0.0 1.1.1.254 0 100 0 54 50 60 i
*> 112.0.0.0/7 0.0.0.0 100 32768 54 50 60 i
s>i113.0.0.0 1.1.1.254 0 100 0 54 50 60 i
*>i114.0.0.0 1.1.1.254 0 100 0 54 i
*>i115.0.0.0 1.1.1.254 0 100 0 54 i
*>i116.0.0.0 1.1.1.254 0 100 0 54 i
*>i117.0.0.0 1.1.1.254 0 100 0 54 i
*>i118.0.0.0 1.1.1.254 0 100 0 54 i
*>i119.0.0.0 1.1.1.254 0 100 0 54 i

I tried it on two differenet IOS version with same result,I am missing something here?

-Imran

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Received on Sat Apr 17 2010 - 21:32:57 ART