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Can one router interface have two networks / subnets?


Dear experts,

Would like to ask you guys,
is it possible to have two networks / subnets on one switch / hub connected to ONLY ONE router interface (eth0)?
The router would have routing entries for both networks / subnets.

The example is as below:

    (Network A) PC --|
                     |
                     |--- X (Router C) -- WAN -- X --- Net
                     |eth0
    (Network B) PC --|

Network A and B will need to talk to each other, as well
as outgoing to the WAN. Would the router have two IPs (1 from Network A, and 1 from Network B) for the one interface ? As I understand, normally there is only one network connected to one interface so I am wondering if more than 1 network/subnet can be put per interface.

Please advice if this can be done and why..
Thanks!

0
Haho
Asked:
Haho
1 Solution
 
samriCommented:
Yes, it is possible.  Just assign an IP address from the 2nd network to the eth0 port on the router.

I'm not sure on the maximum number of secondary IP can be assign to an interface.  I believe it would be product specific.

In addition, I believe you need to establish proper routing in the router, so that it knows where to forward the packet to depending on the target network.

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ahoffmannCommented:
Router C needs an IP from each network, then a network route using this IP, that's all
All PC on network A and B use Router C as default gateway.
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Steve JenningsIT ManagerCommented:
samri has given you the correct answer. In the Cisco world you'd simply add a secondary IP address, so the config would look like:

int e0/0
ip address 10.1.1.1 255.255.255.0
ip address 50.1.1.1 255.255.255.0 secondary


Steve
0
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samriCommented:
SteveJ:
Just q quick question; I remember somebody told me that there is a limit on Cisco on the number of secondary Ip that you could assign to an interface.

and.  you sounds like somebody I knew...

cheers.
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Steve JenningsIT ManagerCommented:
samri;

I've got 5 in addition to the primary on one router interface -- a VXR 7206 running 12.2(5). I run EIGRP and OSPF and I haven't had any problems that I could trace to the multiple IP address setup.

I would guess that the upper limit on IP addresses per interface would have something to do with how buffer space is allocated . . .


Haho;

I didn't include any routing config info because I dont know what routing protocols you are running. If you need more detail, post the router model/maker and which routing protocols you are using.

Good luck.
Steve
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HahoAuthor Commented:
steve,

it is basically going to run static routing ...
the other interface is basically a WAN point-to-point link.
no problems is it?

Thanxs
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cheechewCommented:
Router normally allow you to put many ip on an interface. That seldom people come this limitation that affecting the implementation. Even can have many logical interfaces as well. That is what people doing on the colocation business. The limitation most likely will be the bandwitdh usage available on the interface itself.
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Steve JenningsIT ManagerCommented:
Haho,

You'll have no problems.

Good luck.
Steve
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