EIGRP redistribution

[sukesh tandon]

hi,

I have three routers R1 connected to R2. and R2 is connected to R3 ..One interface os R2 is advertised in ospf and other in EIGRP.

R1

int s0/0/0

ip address 10.1.1.1 255.255.255.252

router ospf 1

net 10.1.1.1 0.0.0.0 area 0

R2

int s0/0/0

ip address 10.1.1.2 255.255.255.252

int s0/1/0

ip address 10.2.2.1 255.255.255.252

router ospf 1

net 10.1.1.2 0.0.0.0

router eigrp 1

net 10.0.0.0

no auto-summary

R3

int s0/1/0

ip address 10.2.2.2 255.255.255.252

router eigrp 1

net 10.0.0.0

I have a doubt that when i m advertising 10.0.0.0 net in EIGRO with no auto summary command.what difference does this no uto summary command make during redistribution.

Thanks

Sukesh Tandon.

Dimension data

[Bilal Nawaz]

Hello, the auto summary is normally enabled by default, e.g. Eigrp, RIP
Auto summary automatically summarises the 'network x.x.x.x' command and advertises these out as classful networks

With your config, there will be no auto summary that is active.

R1
int s0/0/0
ip address 10.1.1.1 255.255.255.252

router ospf 1
net 10.1.1.1 0.0.0.0 area 0

###(Enabled only on s0/0/0 and will advertise specific prefix)

R2
int s0/0/0
ip address 10.1.1.2 255.255.255.252

int s0/1/0
ip address 10.2.2.1 255.255.255.252

router ospf 1
net 10.1.1.2 0.0.0.0

### (Will only enable ospf on s0/0/0 and will advertise out specific prefix)

router eigrp 1
net 10.0.0.0
no auto-summary
### (enables EIGRP on both interfaces and advertises out specific prefix of interfaces because no auto summary command is configured)

R3
int s0/1/0
ip address 10.2.2.2 255.255.255.252

router eigrp 1
net 10.0.0.0

### (auto summary is enabled by default and I assume this will enable EIGRP on the interface and will advertise out specific prefixes - it's meant to advertise the summary right?)

Auto-summary: When a router running Eigrp and has Auto-summary enabled, this router summarizes all network updates between (DIFFERENT MAJOR NETWORK BOUNDARIES).

This means, if the major network between different routers running eigrp with auto-summary enabled are the SAME, then it WILL NOT summarize any network updates.

R1 ---- R2 ---- R3

E.g. If R1 and R2 was sharing a 192.168.1.0 network and R3 is connected to R2 sharing a 10.1.1.1 network. Lets say that R2 had auto summary enabled.

On R2 we have

Router Eigrp 1
Network 192.168.0.0
Network 10.0.0.0


By default auto summary is enabled. It will advertise out the 10.0.0.0 /8 network to R1

But in your case all your routes and addresses live in the 10 network, therefor will only advertise prefix and not summary.

And it makes sense right? You can't go and advertise out the whole 10 network when another connected router has a 10 network off of another interface!

This is my understanding. Hope this helps

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