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2 VLAN, 1 internet modem per VLAN and all talking

mexlg
Occasional Visitor

2 VLAN, 1 internet modem per VLAN and all talking

Hi, I have this issue,  i need to configure a LAN with 2 "dumbs" ADSL modems, separating the lan with 2 VLANs.



i have a 3Com 5500G Switch and two ADSL modems.  Ppl here wont buy me another equipment.



DESIRED CONFIG:



1. Each VLAN must be able to use the internet using its own modem link.



2. VLANs should communicate with each other.



VLAN 2 - 192.168.2.0 /24,  VLAN 2 interface 192.168.2.1, ADSL Modem 2 IP 192.168.2.250



VLAN 3 - 192.168.3.0 /24,  VLAN 3 interface 192.168.3.1, ADSL Modem 3 IP 192.168.3.250



 



I do understand PC on a VLAN should use the Vlan interface IP to communicate with other VLANS but how do i do to tell a VLAN to route internet traffic through a MODEM on the VLAN not through the vlan interface.



Ive done this at the switch but i dont know how to route internet traffic PER VLAN using a defined IP at that VLAN.



SETTING UP VLAN AND VLAN INTERFACE



vlan 2




int vlan2




ip address 192.168.2.1 24




quit




vlan 3




int vlan3




ip add 192.168.3.1 24




quit




SETTING UP PORTS UNTAGGED TO DESIRED VLAN :




For those at VLAN 2




int giga1/0/1




port link-ty hybrid




port hybrid vlan 2 untagged









For those at VLAN 3




int gi1/0/13




port link-ty hy




port hy vlan 3 un




Everything is fine here with PC configuring its Default Gateway with the IP of their VLAN interface, but what about internet link i CANT hit the internet.



Plz remember i have TWO Modems, one per VLAN.  MODEM 2 should connect VLAN 2, MODEM 3 should connect VLAN 3 to the internet.  



One modem serving two subnets its NOT an option.




While im writting this i could imagine a DENY ACL at the switch port where the modem plugs telling smt like this pseudo but i dont know that much to configure an ACL, too dumb YET:



@modem2 port: VLAN 3 TRAFFIC IS NOT ALLOWED @ 192.168.2.250,  VLAN 2 TRAFFIC COME IN



@modem3 port:  VLAN 2 TRAFFIC IS NOT ALLOWED @ 192.168.3.250,  VLAN 3 TRAFFIC COME IN



 



thanks...



The LG



2 REPLIES
ShaunHayward
Occasional Visitor

Re: 2 VLAN, 1 internet modem per VLAN and all talking

I have a problem very simlar to this - did you ever manage to get this sorted?

 

If so,.. how :D

 

cheers

jborg
Visitor

Re: 2 VLAN, 1 internet modem per VLAN and all talking

The solution would probably be to use VRF-Lite, i.e. one "ip vpn-instance" per VLAN. This is because you need a default gateway separately per VLAN, thus a separate routing table. This is a little more involved than just switching, but there are good examples of it in the documentation.