Subinterface OverLaping e0/0

[roberhronek]

Hi there I have an issue with overlapping. Because I still do not understand it properly.

I have a router where I configure 5xDHCP pools, with 192.168.10.x and with 5 sub interfaces for 5 Vlans (e0/0.10, e0/0.20...), and I need configure the physical interface gateway for them physical gateway of that router. Virtual gateway are already configured. At those pictures are sub-interfaces with vlans on one physical interface.

Thanks for advice.

[Richard Burts]

I do not understand the question here. The posting seems to suggest some overlap. But I see only 5 configured subinterfaces with no overlap, and 5 DHCP pools which have no overlap. Is there a problem here? If so what is it?

[roberhronek]

I can not add IP address into the physical interface on that router and showing me the overlapping with Vlan 20 (attached file). 

[Richard Burts]

Thank you for the clarification. There was not anything in the original post that detailed what you were trying to do on the physical interface. The error message indicated overlap with vlan 20, and in fact the address you are attempting to configure on the physical interface overlaps with all 5 of your vlans. The address you are attempting to configure on the physical interface is the /24 which you have subdivided using VLSM logic and assigned to the subinterfaces. I am not clear why you thought you should configure the /24 and then also configure each of the subnets. That does not work.

Let me try to explain the Cisco logic in this way:

- when you configure a router interface with subinterfaces it is a clear indication that the intent is that the physical router interface will connect to a switch port which is configured as a trunk and will carry multiple vlans. 

- on the switch the frames in most of the vlans will be tagged to indicate their vlan membership.

- the frames in one of the vlans will not be tagged and this is called the native vlan. By default the native vlan is usually vlan 1 but the switch can be configured to have some other vlan as the native vlan.

- The subinterfaces on the router are configured with vlan identifiers which allow the subinterface to recognize the vlan membership tag for which it is to process. 

- if an IP address is configured on the physical interface of the router then this interface will process frames in the native vlan.

- we do not know if the switch is actively using the native vlan (and your description seems to imply that it is not). But if the switch were using the native vlan it would not work to assign the /24 network to the native vlan and to assign the /25 (which is the first half of that /24) to vlan 20. This is the overlap that the message describes.

[roberhronek]

Switch is not using active native Vlan 1. 

I do not want to configure each subnets/subinterface separately, but what I want is to assign the IP address into the e0/0 (as a physical interface not virtual interface) as a GW of that router.

Those Vlans are configure with different mask: 10:/28, 20:/25, 30:/29,40:/26 and 50:/29. 

Can I unconfigure or delete the default gateway (subinterfaces - ex: for e0/0.20 - 192.168.10.126), and just use the same physical IP address for each Vlan? 

So which IP address should I assign into that interface, since the /24 is not working and doing the overlaps, if above solution is pointless or wrong.

Thanks

[Richard Burts]

Thanks for clarifying that vlan 1 (native vlan) is not being used. I am not clear about your environment or about what you are trying to achieve. 

If you really want to remove the subinterfaces then you certainly can do that. But I am not sure that you really want to remove them. If you want to use the DHCP scopes that you have showed to us then the subinterfaces must be in the config. If you remove the subinterfaces then the DHCP scopes will not work.

You have shown us only a very small part of the router configuration. The part that you have shown (the DHCP scopes and the subinterfaces) seem appropriate. Assuming correct corresponding configuration on the switch (configuration of the 5 vlans, assignment of access ports to the vlans, configuration of a trunk carrying the 5 vlans) I would expect this part to work.

You indicate that something is not working. But we dont know anything about that part of the router. Can you give us us clarification of what you are trying to achieve and how the rest of the router is configured?

[roberhronek]

This is my whole topology and I need (planning to do) to configure BGP in the topology. And I want to ping PCs to PCs over the topology. and later to configure VPN connections site-to-site. and AS1 just leave as a frame relay. 

[roberhronek]

I can send you more if its needed to verify my decision to have IP address on Router GW. 

[Richard Burts]

Thank you for the drawing. It shows a quite ambitious project. For now I suggest that we not consider the entire project but that we focus on the one router. When we have resolved issues with that router we can consider other aspects of the project.

As I explained if you want to have 5 vlans communicate with the router using a single physical interface of the router then you need the subinterfaces with IP addresses on the router. Doing this will allow the DHCP pools to operate and assign addresses to the clients in the various subnets. So the subinterfaces seem to be a requirement for the way that you have set up the vlans on the switch and the router. I do not understand your comment about "my decision to have IP address on Router GW." Can you provide some clarification about that? I can understand wanting to have addresses on the e1/0 to provide a gateway to the rest of the network. But what reason do you believe for wanting an IP address on the physical interface e0/0? 

[roberhronek]

The reason for that is I need put the IP address into the OSPF network to advertise, and it should be the GW of the e0/0, or should I use the wild mask: network 192.168.10.0 0.0.0.3 area 0? for advertising? 

[Richard Burts · Accepted solution]

I do not understand your references to the gateway of the e0/0? An interface does not have a gateway. A subnet configured on an interface or on a subinterface has a gateway. But the interface itself does not have a gateway. 

Network entry for OSPF is a good idea. But the entry you suggest is not good

network 192.168.10.0 0.0.0.3 area 0

This would advertise vlan 20 (which has the subnet and address that match this statement) but would not advertise the rest of the network. You should use this 

network 192.168.10.0 0.0.0.255 area 0

[roberhronek]

Thank you very much for the answer I was looking for.

but now I have another issue with static NAT, at topology I need configure NAT on Router (SoDR1), I have subinterfaces on the Router because of the Vlans on one physical interface (e0/0) as a INSIDE and another two Links  (e1/0 and e1/1) as OUTSIDEI am using the route map, and ACCESS-list, but its not working as I want to, and also ip route 

ip route 0.0.0.0 0.0.0.0 10.0.15.1

ip route 0.0.0.0 0.0.0.0 10.0.16.1

If you can help me with that, because I do not know why its not working. 

access-list 1 permit 192.168.10.0 0.0.0.255

ip nat inside source route-map SP1 int e1/0 overload

ip nat inside source route-map SP2 int e1/1 overload

int e1/0

ip nat outside

int e1/1

ip nat outside

int e0/0.10

ip nat inside

int e0/0.20

ip nat inside

int e0/0.30

ip nat inside

int e0/0.40

ip nat inside

int e0/0.50

ip nat inside

route-map SP1 permit 10

match ip address 10

match int e1/0

route-map SP2 permit 10

match ip address 1

match int e1/1

[Richard Burts]

There might be more than 1 issue and if so we will deal with it. But the first issue I see is that route map SP1 is matching access list 10 and it should be matching access list 1.

[roberhronek]

So I changed it to this: 

ip nat inside source route-map SP1 interface Ethernet1/0 overload

ip nat inside source route-map SP2 interface Ethernet1/1 overload
ip route 0.0.0.0 0.0.0.0 10.0.15.1
ip route 0.0.0.0 0.0.0.0 10.0.16.1
!
access-list 10 permit 192.168.10.0 0.0.0.255
!
route-map SP2 permit 10
match ip address 1
set ip next-hop 10.0.16.1
!
route-map SP1 permit 10
match ip address 1
set ip next-hop 10.0.15.1

And if I type sh ip nat statistic or translations - showing nothing

[Richard Burts]

Thanks for the additional information. In doing this testing are you doing something from a device connected in one of the vlans that would be going to an Internet destination before you run the show command?

Perhaps it might be helpful if you would do a traceroute from a device connected on one of the vlans to an Internet destination, then do the show command and post both the output of the traceroute and of the show command.