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Beginner

packettracer Vlans and a Router

guys,

 

i need some help.

I have been playing with PT since yesterday and reading many totorials/watching many movies but i am confused.

I created 2 2950 switches in my PT(they are layer 2?) with three vlans; 10,20 and 99.

Port 24 on both switches are Trunk's

But now i am trying to find out how to connect them to a router(dont matter which one) so they can communicate through the router. I am reading a lot about router on a stick and inter-vlan routing(this is only for layer 3 switches?), but i cannot figure out what i need to use.

 

I also noticed the 2950 has no dhcp option, is that correct? I used the code, didnt get an error, but dhcp isnt working. If i need to install dhcp at a router, how is this dhcp able to get its leases to multiple vlans?

 

Hope someone can help.

regards.

10 REPLIES 10
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VIP Mentor

Re: packettracer Vlans and a Router

Hello,

 

post the Packet Tracer project file as a zipped file here, so we can configure the router on a stick and/or use one of the switches as layer 3...

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Beginner

Re: packettracer Vlans and a Router

Thanks for the info and the offer but i would like to try it bymyselve.

Can you advice a ROAS tutorial? And when should i use ROAS and when not?

 

Also, about the dhcp part, how do i know if a switch can act as dhcp and when in cannot? I always though a layer 2 doesnt support dhcp but after reading several posts that say they might, i am somewhat confused.

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VIP Mentor

Re: packettracer Vlans and a Router

Hello,

 

I was asking for the project file to see how your devices are connected. Two switches, both connected to the router directly, or daisy-chained ?

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Beginner

Re: packettracer Vlans and a Router

i have been playing with both situation,

I added ta printscreen from the empty situation(without any configuration)

Highlighted
Enthusiast

Re: packettracer Vlans and a Router

ops, did not see your picture till now.
picture shows L2 switches and routers , no L3 switch at all. see my reply below

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Enthusiast

Re: packettracer Vlans and a Router


yes, if u want to use L2 switch only, use a router on a stick, must use ROAS.
if you want to use l3 switch, you can do it with SVI , aka interface vlan x , for so called inter-vlan routing on L3 switch

DHCP in PT can be set up on router or Server. However, I think DHCP on a router may still NOT work properly - it did not in the previous versions of PT but i have not check this in PT 7.3. it is just limitation of PT - not all features will work


DHCP service works well on Server box.

 

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

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Beginner

Re: packettracer Vlans and a Router

So i cannot use dhcp with a switch?

Also, how dow i know if a switch is L2 or L3?

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Enthusiast

Re: packettracer Vlans and a Router

cannot use dhcp with on any switches or routers in Packet tracer (limit of PT software);
use DHCP tab on Server in PT - drag and drop server .


L2 switches are models 2950 and 2960 - look at icon of a switch, different from or L3.
L3 switches are called multi-layer switch.  like 3560, 3650, 3750, 3850, - icon is bigger then L2 one


There are FREE examples (samples) of different networks/labs/set-ups in PT software.  I think it is  File >Open > Samples  
Or  File > Open Samples 

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Enthusiast

Re: packettracer Vlans and a Router

or try my old file , should work in PT 7.x version

un-zip it first 

 

Highlighted
Hall of Fame Master

Re: packettracer Vlans and a Router

It is an unfortunate limitation that PT does not work for DHCP. The original poster has asked several questions which I would like to answer:

- "So i cannot use dhcp with a switch?" Aside from the limitation in PT I can say that with actual Catalyst switches you should be able to implement DHCP.

- "how dow i know if a switch is L2 or L3" The most important point is to look in the configuration and see if the command ip routing is present. If that command is present then the switch is operating as layer 3. You might also try the command show ip protocol and see what it says.

- in the original post you asked " If i need to install dhcp at a router, how is this dhcp able to get its leases to multiple vlans?" Part of the answer is that if there are multiple vlans, then there will be multiple subnets used, and the router can configure multiple DHCP scopes (one per vlan) where each DHCP scope has its own DHCP pool, its own default router, and possibly other DHCP parameters. When the router receives a DHCP request from a client it looks to see which vlan/which subnet originated the request and uses the appropriate DHCP scope to select an appropriate address to use.

Another factor to consider is whether the router with the DHCP scopes is directly connected to the vlan/subnet where the client is connected or whether the router is remote from the client vlan/subnet. If the router is directly connected to the client subnet then the router knows where the request came from and can respond. If the router is remotely connected to the client then the device doing the layer 3 routing for the client will have configured ip helper-address to identify the DHCP server. In this case the DHCP request will include a field for the gateway address and the DHCP router will use that field to determine which DHCP scope to use.

HTH

Rick