RIPv2 Auto-summary

TK1979TK1979 Posts: 2Registered Users ■□□□□□□□□□
I was doing one of the INE workbook exercises where the task was simple enough, re-enable auto-summary for RIP and observe the changes to what is advertised. I couldnt get my head around a few things. Here is the output of the interfaces and RIP config:

Ethernet0/1.45 155.1.45.4 YES TFTP up up
Loopback0 150.1.4.4 YES TFTP up up
Tunnel0 155.1.0.4 YES TFTP up up

router rip
version 2
network 150.1.0.0
network 155.1.0.0
no auto-summary

Now once auto-summary is re-enabled the debug output is below as well as the explanation from INE but what i cant understand is:
the 150.1.4.4/32 route changed after auto-summary was enabled, but why did the 155.1.0.0/24 route stay the same and not change to a /16 address


Before auto-summary is enabled:

R4#debug ip ripRIP: sending v2 update to 224.0.0.9 via GigabitEthernet1.45 (155.1.45.4)RIP: build update entries 150.1.4.4/32 via 0.0.0.0, metric 1, tag 0 155.1.0.0/24 via 0.0.0.0, metric 1, tag 0RIP: sending v2 update to 224.0.0.9 via Tunnel0 (155.1.0.4)RIP: build update entries 150.1.4.4/32 via 0.0.0.0, metric 1, tag 0 155.1.45.0/24 via 0.0.0.0, metric 1, tag 0After auto-summary is enabled, R4 summarizes the specific 150.1.4.4/32 prefix of its Loopback0 into the 150.1.0.0/16 and sends it outbound on its RIP-enabled interfaces. Because R4's Ethernet interface on VLAN 146 is disabled, there are no RIP updates sent or received on the interface.


RIP: sending v2 update to 224.0.0.9 via GigabitEthernet1.45 (155.1.45.4)RIP: build update entries 150.1.0.0/16 via 0.0.0.0, metric 1, tag 0 155.1.0.0/24 via 0.0.0.0, metric 1, tag 0RIP: sending v2 update to 224.0.0.9 via Tunnel0 (155.1.0.4)RIP: build update entries 150.1.0.0/16 via 0.0.0.0, metric 1, tag 0 155.1.45.0/24 via 0.0.0.0, metric 1, tag 0

Comments

  • bermovickbermovick Posts: 1,134Member ■■■■□□□□□□
    Auto-summarization only happens when crossing a classful boundary, which isn't being done on G1.45 for the 155.x.x.x network.


    Create a G1.54 interface between R4 and R5, put them in a 156.1.45.x/24 subnet and enable RIP and you'd see the 155 network get summarized when being sent out the 1.54 interface then.
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  • TK1979TK1979 Posts: 2Registered Users ■□□□□□□□□□
    Ok i think i get it, thnx
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