What does known via "connected" exaclty mean

Answered Question
Feb 5th, 2008

c2611#sh ip route 192.168.1.101

Routing entry for 192.168.1.0/24

Known via "connected", distance 0, metric 0 (connected, via interface)

Redistributing via eigrp 1

Routing Descriptor Blocks:

* directly connected, via FastEthernet0/0

Route metric is 0, traffic share count is 1

on the fe0/0 is a switch. How is a connected interface routing?

I have this problem too.
0 votes
Correct Answer by Jon Marshall about 8 years 11 months ago

"Is it only learning about this network becuase I have an interface configured on the router with the 10.10.10.2 /24 address"

Yes.

the 192.168.50.1 interface. The route will only appear in the routing table if the interface is up.

Jon

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andrew.butterworth Tue, 02/05/2008 - 09:45

What it means is this network is directly reachable via a local interface on the router because it has an IP address in the network. If you look at the configuration of your router you should see something like:

interface FastEthernet0/0

ip address 192.168.1.254 255.255.255.0

When the router receives a packet (on a different interface) with a destination address in the network 192.168.1.0/24 it makes a routing decision and knows that it has an interface directly attached to this network. It will then check it's ARP table for the destination IP address and forward it directly at Layer-2 (MAC).

HTH

Andy

Danilo Dy Tue, 02/05/2008 - 09:48

Hi,

It's either the IP address is configured in fe0/0 or in the host connected to fe0/0 and in the same network of the IP address configured in fe0/0.

They are categorize as local network or local route because routing is network-oriented, IP makes routing decisions based on the network portion of the address. The IP module determines the network part of the destination's IP address by applying the network mask to the address. If the destination network is the local network, the mask that is applied may be the local subnet mask. If no mask is provided with the address, the address class determines the network portion of the address.

After determining the destination network, the IP module looks up the network in the local routing table. Packets are routed toward their destination as directed by the routing table. The routing table may be built by the system administrator or by routing protocols, but the end result is the same; IP routing decisions are simple table look-ups.

Regards,

Dandy

brooklynheight Tue, 02/05/2008 - 10:32

correct 192.168.1.250 is the fe0/0 interface

on my router.

I noticed the eigrp statement.

Is there a routing statement or does the 1.0

need to be placed in a routing table in order

for the local router to be able to reach it?

Or is this learned via arp..and than populated as "connected" in the routing table

Jon Marshall Tue, 02/05/2008 - 11:42

If i understand correctly, no there is no specific route for this.

As long as the interface address is covered by a network statement under your EIGRP config eg.

router eigrp 1

network 192.168.1.0

then EIGRP will automatically redistribute the connected interfaces into the EIGRP process.

Hope i have understood

Jon

brooklynheight Tue, 02/05/2008 - 12:17

what about in this case

c4506#sh ip route 10.10.10.3

Routing entry for 10.10.10.0/24

Known via "connected", distance 0, metric 0 (connected, via interface)

Routing Descriptor Blocks:

* directly connected, via Vlan1

Route metric is 0, traffic share count is 1

I see no routing statement for the 10.10.10.0

network. However there is an vlan interface 10.10.10.2.

The reason I ask becuase I configured an FE

with an ip address of 192.168.24.1/24

the .24.0 never showed as connected in the route table.

I was under the impression from the above comments that it would appear in the route table as connected because a local interface was configured with that subnet/network

Jon Marshall Tue, 02/05/2008 - 12:23

Hi

When you say you see no routing statement for 10.10.10.0 what exactly do you mean ?

If there is an interface with an IP of 10.10.10.2 255.255.255.0 then the directly connected network should show up in the output of a "sh ip route"

10.10.10.0 is directly connected, vlan 1

Not sure i follow in the 192.168.24.0. Again, if you have an interface configured with a 192.168.24.x address then it should show up in a "sh ip route" eg.

192.168.24.0 is directly connected, fa0/0

Jon

brooklynheight Tue, 02/05/2008 - 13:18

There in lies my question

How does the router know to put the 10.10.10.0 in the routing table if there is no explcit routing statement for this route?

Is it only learning about this network becuase I have an interface configured on the router with the 10.10.10.2 /24 address?

If this is the case-I configured 192.168.50.1

on a router interface. But the 192.168.50.0

network never showed up in the sh ip route table......shouldnt it have shown up as connected?

Correct Answer
Jon Marshall Tue, 02/05/2008 - 13:21

"Is it only learning about this network becuase I have an interface configured on the router with the 10.10.10.2 /24 address"

Yes.

the 192.168.50.1 interface. The route will only appear in the routing table if the interface is up.

Jon

andrew.butterworth Tue, 02/05/2008 - 13:23

The router doesn't need to learn about how to get to network 10.10.10.0/24 since it is directly connected to this network via it's VLAN-1 interface. The subnet mask dictates how the networks appear in the routing table. For example if you had configured 192.168.10.1/29 then you would have a connected route for 192.168.10.0/29. The '.1' part of the address is just the routers interface onto this network.

Andy

brooklynheight Tue, 02/05/2008 - 18:20

great thx!

I think is what confused me is when i configured the interface it did not appear in the routing table as connected..becuase the interface wasnt UP UP

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