can anyone explain the following router output information. thanks

dannan lin · ‎10-03-2011

i just want to know how

Split Horizon works in here.

RIP: build update entries

network 192.168.2.0 metric 1

network 192.168.20.0 metric 2

network 192.168.30.0 metric 1

RIP: sending v1 update to 255.255.255.255 via Serial2/0 (192.168.2.1)

RIP: build update entries

network 192.168.3.0 metric 1

network 192.168.10.0 metric 2

network 192.168.30.0 metric 1

RIP: sending v1 update to 255.255.255.255 via Loopback2 (192.168.30.1)

RIP: build update entries

network 192.168.1.0 metric 2

network 192.168.2.0 metric 1

network 192.168.3.0 metric 1

network 192.168.10.0 metric 2

network 192.168.20.0 metric 2

RIP: received v1 update from 192.168.2.99 on Serial2/0

192.168.1.0 in 1 hops

192.168.10.0 in 2 hops

192.168.20.0 in 1 hops

RIP: received v1 update from 192.168.3.1 on Serial3/0

192.168.1.0 in 1 hops

192.168.10.0 in 1 hops

192.168.20.0 in 2 hops

RIP: sending v1 update to 255.255.255.255 via Serial3/0 (192.168.3.99)

RIP: build update entries

network 192.168.2.0 metric 1

network 192.168.20.0 metric 2

network 192.168.30.0 metric 1

RIP: sending v1 update to 255.255.255.255 via Serial2/0 (192.168.2.1)

RIP: build update entries

network 192.168.3.0 metric 1

network 192.168.10.0 metric 2

network 192.168.30.0 metric 1

RIP: sending v1 update to 255.255.255.255 via Loopback2 (192.168.30.1)

RIP: build update entries

network 192.168.1.0 metric 2

network 192.168.2.0 metric 1

network 192.168.3.0 metric 1

network 192.168.10.0 metric 2

network 192.168.20.0 metric 2

RIP: received v1 update from 192.168.2.99 on Serial2/0

192.168.1.0 in 1 hops

192.168.10.0 in 2 hops

192.168.20.0 in 1 hops

thanks for your help, i just want to know how to see

how Split Horizon works in here.

sorry i am newbie to the cisco. much appreciated.

turbo_engine26 · ‎10-11-2011

Dannan,

It will be much helpful if you post the network layout in order to get the needed answer.

Split Horizon is a mechanism to prevent a learned route to get advertised back to its originator. From the debug output, i can't tell which interfaces are connected to which interfaces.

HTH

A.M.

Richard Burts · ‎10-11-2011

AM

It is a bit like working out a puzzle. When you look at the messages posted there are clues:

RIP: sending v1 update to 255.255.255.255 via Serial2/0 (192.168.2.1)

so interface serial2/0 is 192.168.2.1

RIP: sending v1 update to 255.255.255.255 via Serial3/0 (192.168.3.99)

so interface serial3/0 is 192.168.3.99

RIP: sending v1 update to 255.255.255.255 via Loopback2 (192.168.30.1)

so interface loopback2 is 192.168.30.1

So we can determine that there are 3 local interfaces and now we know what networks are connected to each

serial2/0 192.168.2.0

serial3/0 192.168.3.0

loopback2 192.168.30.0

Now when we look at the output posted we can see that the local networks are being advertised. And we can see that some remote networks are being learned (focus on the messages about received update)

RIP: received v1 update from 192.168.2.99 on Serial2/0

192.168.1.0 in 1 hops

192.168.10.0 in 2 hops

192.168.20.0 in 1 hops

RIP: received v1 update from 192.168.3.1 on Serial3/0

192.168.1.0 in 1 hops

192.168.10.0 in 1 hops

192.168.20.0 in 2 hops

so there are 3 remote networks being learned and the same 3 networks are learned from each remote neighbor (serial2/0 and serial3/0)

So now we can understand that the routing table consists of these entries (and how they are learned)

192.168.1.0 remote via both serial2/0 and 3/0

192.168.2.0 connected on serial2/0

192.168.3.0 connected on serial3/0

192.168.10.0 remote via both serial2/0 and 3/0

192.168.20.0 remote via both serial2/0 and 3/0

192.168.30.0 connected on loopback2

so there are 6 entries in the routing table.

So now let us consider how split horizon affects the advertisement of routes. A RIP routing update sent will include all the routes in the table (6 entries) except for any route learned from that interface. The easy case is interface loopback2. Let us look at what is advertised out interface loopback2:

RIP: sending v1 update to 255.255.255.255 via Loopback2 (192.168.30.1)

RIP: build update entries

network 192.168.1.0 metric 2

network 192.168.2.0 metric 1

network 192.168.3.0 metric 1

network 192.168.10.0 metric 2

network 192.168.20.0 metric 2

there is only one network learned from that interface (and not advertised because of split horizon) and the other 5 networks are being advertised.

There is a similar process on interfaces serial2/0 and 3/0. For each interface there is one network that is connected and 2 networks learned with a metric of 1. Split horizon says that these networks will not be advertised out that interface and the other 3 networks will be advertised.

HTH

Rick

HTH

Rick

dannan lin · ‎10-12-2011

thank you very much.

turbo_engine26 · ‎10-12-2011

Please rate if the answer was helpful.

HTH

A.M.

turbo_engine26 · ‎10-12-2011

Hi Richard,

Sure yes, it is a sort of puzzle and i could have solved it but it would take some time to solve. It would be much more faster if the poster of the topic upload the layout as most of us are busy doing other things besides helping people here.

However, that was very smart analysis and explanation from your side. Hats off!

HTH

A.M.