Gateway address for several subnets that can't be superneted in one entry

danielknowlab · ‎09-22-2016

Hi guys!! I've analyzing this case: I need to set the address on interface p2 of R1 to use as gateway for the /24 networks on SW2 - Can not plug SW2 directly to SW1 - Can not use VLANs - Using only Static Route (no protocol)

     [10.10.0.0/24] ---------------------------
                                              |
     [10.10.1.0/24 .. 10.10.3.0/24] ------------[SW1]--------
                                              |             |
     [10.10.4.0/24 .. 10.10.7.0/24] -----------             |                    
                                                            | p1: 10.10.0.0/21
                                                           [R1]------------------....
                                                            | p2: ???.???.???.???/??
                                                            |
                                                            |
     [10.10.8.0/24 .. 10.10.255.0/24] ----------[SW2]--------

Can use only static routes and I see direct and local connections to the interfaces at these networks I think no solution here, because 10.10.8.1/16 overlaps with R1:p1 interface address and can't set a mask to cover all subnets in the gateway. Any idea or solution?? how I must to configure p2 to set correctly the gateway to the sw2 networks? Thanks!!

rasmus.elmholt · ‎09-22-2016

And you can't use secondary addresses on the interfaces either?

If the clients have a /24 subnetmask they won't be able to contact R1 in your diagram because the GW adresses is outside their subnet.

danielknowlab · ‎09-23-2016

No, I don't know how I could do that. But yes the problem is the overlapping on p1 and p2, that are limiting the range covered on p2 mask. p1 is in /21 let communication with all networks on SW1 from 10.10.0.0/24 to 10.10.7.0/24. But p2 can't be /16 because overlaps with p1, then if for example set p2 as 10.10.8.1/24 or any other not at /16 then all SW2 networks range are not covered.

I think that gateway don't need to be connected directly to network range, I think that must be in route resolution. But in this case, the ranges are overlapping and the address on p2 are limited range, for example at /24 here route table:

10.0.0.0/8 is variably subnetted, 7 subnets, 5 masks

C 10.0.0.8/30 is directly connected, Serial0/0/0

L 10.0.0.9/32 is directly connected, Serial0/0/0

C 10.10.0.0/21 is directly connected, GigabitEthernet0/0

L 10.10.0.1/32 is directly connected, GigabitEthernet0/0

C 10.10.8.0/24 is directly connected, GigabitEthernet0/1

L 10.10.8.1/32 is directly connected, GigabitEthernet0/1

S 10.20.0.0/16 [1/0] via 10.0.0.10

I tried too assigning static route explicitly to the GigabitEthernet0/1 instead by the ip of the port to avoid the next hop router itself ip. Any way don't works and i don't believe that this is a good idea for workaround, but anyway it's my testting :)

10.0.0.0/8 is variably subnetted, 8 subnets, 5 masks

C 10.0.0.8/30 is directly connected, Serial0/0/0

L 10.0.0.9/32 is directly connected, Serial0/0/0

S 10.10.0.0/16 is directly connected, GigabitEthernet0/1

C 10.10.0.0/21 is directly connected, GigabitEthernet0/0

L 10.10.0.1/32 is directly connected, GigabitEthernet0/0

C 10.10.8.0/24 is directly connected, GigabitEthernet0/1

L 10.10.8.1/32 is directly connected, GigabitEthernet0/1

S 10.20.0.0/16 [1/0] via 10.0.0.10

At this point, I'm thinking that may be bridging the p2 to p1 may be the solution, not sure.

Any other solution or recommendation?

Thanks!

rasmus.elmholt · ‎09-23-2016

interface p1

ip address 10.10.0.1 255.255.255.0

ip address 10.10.1.1 255.255.255.0 secondary

ip address 10.10.2.1 255.255.255.0 secondary

etc.

danielknowlab · ‎09-23-2016

Ummm ... I solve this with only one address 10.10.0.0 255.255.248.0, for p1, but p2 can't be resumed on one address, then I take your idea and try add secondary ips grouping the SW2 networks ... I'm going to try!!

But, this is the habitual way to solve this?

rasmus.elmholt · ‎09-23-2016

This would be the way to make it work, but it is a workaround for a poor ip addressing scheme.

Normally you wouldn't split networks like this outside the bit boundaries..

danielknowlab · ‎09-23-2016

I'm analyzing as new addressing scheme, the idea is to set 10.A.B.node schema.

10: organization private network

A: brach (internal organization site / geographical network)

B: several subnet for each branch

But in some cases level/groups of subnetworks are need on same brach. This is the analyzing case in post. I don't want/waste to set another "A" range to this split on the branch.

In this case I'm analyzing the branch on 10.10.0.0/16 and splitting for one level 10.10.0.0/21 and other level for the rest range. /21 are not on bit boundary? what best practice for this kind of split?

danielknowlab · ‎09-23-2016

Not working for me, using a Cisco 1941:

ip address 10.10.9.0 255.255.255.0 secondary

^

% Invalid input detected at '^' marker.

But, this is the habitual way to solve this? we need to enter 247 secondary interfaces, this may impact on performance.