2 subnet on single interface..help required

[Mohsin Hussain]

How to configure router interface for two subnets on it , my ISP is providing data link and internet on same ethernet to me , data link local private IP address is my from head office to site office 10 km away from HO ,and internet subnet is public IP for internet . how to configure it on my router fa 0/0 interface .

[johnlloyd_13]

hi,

you can use the ip address 'secondary' interface config command.

Router(config-if)#ip address

secondary

[ALIAOF_]

You can create a sub interface like "fa0/0.1 for your data link", "fa0.0.2 for your Internet".  Ofcourse your ISP's equipment will need to match the settings but they already might have it setup like that.  If you ask them to show you the interface configuration on their device they will show it to you.

[Mohsin Hussain]

Thanks for your reply all .......

@Muhammad Ali : you mean to say to config sub interface , so for my understanding it means at ISP hand they have configured trunk port on there side with 2 vlans allow on it , 1 vlan for data and 1 vlan for internet . Am i right and i have to config encap for that isp config vlans via sub interface right . me to thinking the same.

@ johnlloyd_13: I didnt get it right , i know we can config multiple secondary ip address to interfaces but the thing is that how the isp has config it on there side that i think is important and i should do the same way. if they have configured trunk on there side then do secondary ip option work fine for data subnet and internet subnet if i route the traffic between two office and internet for Head office .

1 more thing to ask .

I have internet running of Head office only and between Head office and Remote Office there is only data connectivity (no internet connection there) how do i share my head office internet connection to remote office user .

Do i 1st have to config routing  between 2 offices and then on head office config the default route and on remote site office config default route to head office connected interface . Am i right ...is the below mention config is right ??

After Config Static route between HO and Site Office .

HO-Router(config)# ip route 0.0.0.0 0.0.0.0 1.1.1.1

Site-Office(config)# ip route 0.0.0.0 0.0.0.0 192.168.1.1

                             .1                     192.168.1.0/30                               .2

             HO-Router--------------------------------------------------------------------------------Site-Office

                     |

                     |

                   ISP (1.1.1.1 Gateway)

[ALIAOF_]

Yes if your ISP is just giving you a single interface and cable then they most likely have their side VLANed.  Ask them to confirm and ask them to send you a "show runn" of the interface on their side.  I'm surprised they did not tell you what you need to do on your end to match the settings.

Once all this is up yes so your default route "HO Router" would be ISP gateway.  And Your remote site depending on how the two are connected (I'm assuming a simple L2 connection) you would send it to 192.168.1.1

[Richard Burts]

I would suggest that we need some clarification from the original poster (and that he might need some clarification from the ISP) about what is intended. So far the discussion assumes that both addresses are to be configured on the same interface. But I would like to suggest the possibility that the ISP has given the private address to be used on the link from the customer router to the ISP router. And that the second subnet is intended to be configured on the customer router inside interface or perhaps as a pool of addresses for address translation. We need to know what the ISP intends before we can give good advice.

HTH

Rick