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Routing Subnet

burhaans28
Beginner
Beginner
5 Accepted Solutions

Accepted Solutions

The first part of your question is petty clear. 10.1.0.0/16 and 10.2.0.0/16 mean that the first 2 octets are used for the network and subnet addressing and that the last 2 octets are available for host addressing or additional subnetting. So you would configure 10.1.1.0/24, 10.1.2.0/24, 10.1.3.0/24, etc resulting in having 256 subnets on each side.

The other parts of your question are less clear. From what I see in the diagram pc0 and pc1 could be in any subnet (or potentially there could be 2 pc in every subnet). Are there any additional instructions about pc0 and pc1? The diagram does not show anything about the subnet/network between R2 and R3. Perhaps it might be a subnet in 10.3.0.0? Are there any additional instructions about this link?

HTH

Rick

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10.1.0.0/16 divided into 256 subnets means use VLSM where network /16 is divided into several subnets with /24 each (asked for 256 subnets).  The picture shows several /24 already; u can use one of those /24 for router to router links but normally router to router link with 2 hosts will use /30. So, PC0 uses 10.1.10.0/24 subnet on vlan 10; PC1 uses 10.1.20.0/24 subnet on vlan 20, etc. This also means u need a Router on a stick, aka ROAS. this router will have several sub-interfaces towards LAN with 802.1Q vlans. Each vlan x belongs to diferent subnet x and sub-interface vlan x. 

Router 2 and 0 will use 10.1.0.0/24 subnet. Router 1 and 3 could use 10.2.0.0/24 subnet. Router 3 to LAN  must be ROAS as well and use 10.2.x.0/24. However, u could take one of those earlier /24 networks and subdivided further into /30 for those p2p2 links.

For example do not use 10.1.0.0/24 subnet on LAN for any PCs and vlans. Use it on router p2p2 links. this means 10.1.0.0/24 subnet is divided into /30, i.e. 10.1.0.0/30, 10.1.0.4/30, 10.1.0.8/30, 10.1.0.12/30....10.1.0.252/30.  Pick and use any /30 for router to  router links.

Alternatively you could use completely different network, i.e. 192.168.x0.0/24 for router to router links

Regards, ML
**Please Rate All Helpful Responses **

View solution in original post

Router2 will be ROAS sharing interface for each subnet that is assigned to PCs. Here is sample of ROAS config:

interface FastEthernet0/0.x

encapsulation dot1Q x

ip address 10.1.x.1 255.255.255.0

!

interface FastEthernet0/0.Y

encapsulation dot1Q Y

ip address 10.1.Y.1 255.255.255.0

 

Router2 is the default gateway for PCs.  Swich1 does not need  to have  IP but if u must then one of subnets must be reserved for swich1 as management vlan. PCs go via swich1 as l2 device and not L3 one.

you can attach your PT file here in a zip format.

 

Regards, ML
**Please Rate All Helpful Responses **

View solution in original post

There are some options about how this could be implemented. I wonder if there are some instructions for this exercise that would specify which option to use. One option would be to treat the switch as a layer 3 switch, do inter vlan routing on the switch, and have the connection from switch to router as a routed link (one subnet on the link). But since the switch is a 2960 I suspect that this is not the option intended.

The option that I believe was intended would be to use the switch as a layer 2 switch. To do this ip routing is not enabled on the switch (which is the default behavior). You would configure multiple vlans on the switch (one vlan for each subnet to be configured). You would not configure SVI for each vlan. You would configure access ports on the switch as members of the various vlans. You would connect PCs to the access ports. You would configure the interface on the switch that connects to the router as a trunk carrying all of the vlans. You would not configure an IP address on the interface connecting the switch and the router. You would configure subinterfaces on the router (a separate subinterface for each vlan being configured). The router subinterface would be configured with an IP address in the appropriate subnet and the router would function as the default gateway for each vlan/subnet. Inter vlan routing would be done on the router. If you want to have an IP address on the switch for management purposes (this would be optional depending on the instructions for the exercise) you would configure an SVI for one vlan and configure an appropriate IP for that SVI.

HTH

Rick

View solution in original post

no, at basic CCNA level, there is no need for IP and SVI on switch 1, unless you want to connect to it to do management, then, you can choose any subnet that is not used by LANs and PCs. You can find some videos on youtube for ROAS.

alternative to ROAS is L3 switch where l3 switch is doing routing for PCs on LAN, not router.

here is my example of ROAS, Only PC0 and PC1 are ok, you can fix it so that PC 3 , 4 ping PC0 and 1.  All PCs should be able to ping all others and switches in the end.

 

Regards, ML
**Please Rate All Helpful Responses **

View solution in original post

12 Replies 12

burhaans28
Beginner
Beginner

Hi i am doing this topology for eigrp, I am confused that what 10.1.0.0/16 divided into 256 subnets means, and what subnet will pc0 and pc1will be in and router 2 will use which subnet

From R2 to R3 which network should i use 

The first part of your question is petty clear. 10.1.0.0/16 and 10.2.0.0/16 mean that the first 2 octets are used for the network and subnet addressing and that the last 2 octets are available for host addressing or additional subnetting. So you would configure 10.1.1.0/24, 10.1.2.0/24, 10.1.3.0/24, etc resulting in having 256 subnets on each side.

The other parts of your question are less clear. From what I see in the diagram pc0 and pc1 could be in any subnet (or potentially there could be 2 pc in every subnet). Are there any additional instructions about pc0 and pc1? The diagram does not show anything about the subnet/network between R2 and R3. Perhaps it might be a subnet in 10.3.0.0? Are there any additional instructions about this link?

HTH

Rick

The 10.1.0.0/16 Network is subnetted into 256 /24 Subnets, implemented as VLANS on Switch 1. The same is done for  10.2.0.0/16 on Switch2. These should be connected to the routers by Trunk links.

You need only configure the first 2 of these subnets on each side:

10.1.0.0/24                        10.2.0.0/24
10.1.1.0/24                        10.2.1.0/24

You also only need to configure PCs on the first two subnets on each side

suppose i use subnet 10.1.0.0/24 for pc0

and subnet 10.1.1.0/24 for pc1

so which ip should i use from swich1 to Router 2

so on int gig0/0 which ip should i give

 

 

Router2 will be ROAS sharing interface for each subnet that is assigned to PCs. Here is sample of ROAS config:

interface FastEthernet0/0.x

encapsulation dot1Q x

ip address 10.1.x.1 255.255.255.0

!

interface FastEthernet0/0.Y

encapsulation dot1Q Y

ip address 10.1.Y.1 255.255.255.0

 

Router2 is the default gateway for PCs.  Swich1 does not need  to have  IP but if u must then one of subnets must be reserved for swich1 as management vlan. PCs go via swich1 as l2 device and not L3 one.

you can attach your PT file here in a zip format.

 

Regards, ML
**Please Rate All Helpful Responses **

So Router on a stick is only option for pc traffic to go out from Router2

and for router2 int gig0/0 towards switch 1 which ip address should i assign 

There are some options about how this could be implemented. I wonder if there are some instructions for this exercise that would specify which option to use. One option would be to treat the switch as a layer 3 switch, do inter vlan routing on the switch, and have the connection from switch to router as a routed link (one subnet on the link). But since the switch is a 2960 I suspect that this is not the option intended.

The option that I believe was intended would be to use the switch as a layer 2 switch. To do this ip routing is not enabled on the switch (which is the default behavior). You would configure multiple vlans on the switch (one vlan for each subnet to be configured). You would not configure SVI for each vlan. You would configure access ports on the switch as members of the various vlans. You would connect PCs to the access ports. You would configure the interface on the switch that connects to the router as a trunk carrying all of the vlans. You would not configure an IP address on the interface connecting the switch and the router. You would configure subinterfaces on the router (a separate subinterface for each vlan being configured). The router subinterface would be configured with an IP address in the appropriate subnet and the router would function as the default gateway for each vlan/subnet. Inter vlan routing would be done on the router. If you want to have an IP address on the switch for management purposes (this would be optional depending on the instructions for the exercise) you would configure an SVI for one vlan and configure an appropriate IP for that SVI.

HTH

Rick

10.1.0.0/16 divided into 256 subnets means use VLSM where network /16 is divided into several subnets with /24 each (asked for 256 subnets).  The picture shows several /24 already; u can use one of those /24 for router to router links but normally router to router link with 2 hosts will use /30. So, PC0 uses 10.1.10.0/24 subnet on vlan 10; PC1 uses 10.1.20.0/24 subnet on vlan 20, etc. This also means u need a Router on a stick, aka ROAS. this router will have several sub-interfaces towards LAN with 802.1Q vlans. Each vlan x belongs to diferent subnet x and sub-interface vlan x. 

Router 2 and 0 will use 10.1.0.0/24 subnet. Router 1 and 3 could use 10.2.0.0/24 subnet. Router 3 to LAN  must be ROAS as well and use 10.2.x.0/24. However, u could take one of those earlier /24 networks and subdivided further into /30 for those p2p2 links.

For example do not use 10.1.0.0/24 subnet on LAN for any PCs and vlans. Use it on router p2p2 links. this means 10.1.0.0/24 subnet is divided into /30, i.e. 10.1.0.0/30, 10.1.0.4/30, 10.1.0.8/30, 10.1.0.12/30....10.1.0.252/30.  Pick and use any /30 for router to  router links.

Alternatively you could use completely different network, i.e. 192.168.x0.0/24 for router to router links

Regards, ML
**Please Rate All Helpful Responses **

Pc0 uses 10.1.10.0/24 subnet on vlan 10

Pc1 uses 10.1.20.0/24 subnet on vlan 20

do i have to create svi on switch 1

and for router2 int gig0/0 towards switch 1 which ip address should i assign 

no, at basic CCNA level, there is no need for IP and SVI on switch 1, unless you want to connect to it to do management, then, you can choose any subnet that is not used by LANs and PCs. You can find some videos on youtube for ROAS.

alternative to ROAS is L3 switch where l3 switch is doing routing for PCs on LAN, not router.

here is my example of ROAS, Only PC0 and PC1 are ok, you can fix it so that PC 3 , 4 ping PC0 and 1.  All PCs should be able to ping all others and switches in the end.

 

Regards, ML
**Please Rate All Helpful Responses **

I am glad that our suggestions have been helpful. Thank you for marking this question as solved. This will help other participants in the community to identify discussions which have helpful information. This community is an excellent place to ask questions and to learn about networking. I hope to see you continue to be active in the community.

HTH

Rick

Thank you so much, your guidance is very helpful for student like me.

You are welcome.

HTH

Rick
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