I've been give a scenario for ma assignment, where one network is divided into 4 subnets having one server each. however, the hosts(icluding the server) inside a subnet are all connected to a switch and likewise we are having four swithes for 4 subnets, and these switches are all connected to a router, which is in turn connected to Internet. thats' it. ma problem is, how to use interior gateway protocol (like OSPF, IS-IS) for this scenario as there is no more router to communicate. it is only a one router network. Is the protocols are only for router to roter commuvication or router to switch is also possible.


Thanx in advance....

A s i F.............

switches don't do ip routing which means that all connected devices will be on the same IP subnet

well no, not at all really. assuming that these a basic layer2 switches, and the router has for lan interfaces, then each switch would server a seperate subnet, indeed would have to if it's a conventional router with non-switching interfaces on it. additionally switchs *can* route if you pick the right ones, i.e. layer 3 switches, and so can run ospf. the bit i see is that as there is only one router, there is nothing to use ospf.. what's the point of it? you could nominally configure ospf on the router, but this is pointless as the OP appears to be aware. if this is really for an MA project, then surely there's something missing here, the topology defined is really pretty dull and basic, and nowhere near anything deserving of an MA level education.

what, you mean to tell me I can make different IP subnets by using switches?

make? if you wish to route on a switch you need a layer 3 switch. "routing" is actually, packet switching at osi layer 3 rather than "switching" normally being layer 2 switching. the processes are actually very similar just based on ip's not mac adresses. but a normal switch won't do this, you'd be looking at somethign more up market. whilst this is a switch, so are these bad boys. snother factor worth remembering is also that the cheaper simpler switches will also happily misbehave if told to and you can run multiple seperate ip subnets on a single just by plugging different networks into it, as simple switches are layer 2 not layer 3, so have no understanding of ip addresses at all, so don't care.

Right little bit out of my league them cisco ones

From the description given it sounds like the "project" is to setup 4 subnets on the same physical network and configure the router to handle all 4 subnet routing.

Since there is only one router you do not need any of the router protocols that normally would be needed to inform the router about different hosts on the subnets as all the subnets are directly connected to the router. If all the hosts are entered statically into the routing table then you would not need any route discovery protocols but if the hosts are added and removed on the subnets I would suggest using one of the RIP protocol versions to keep the routing tables up to date - saves on having to change the routing table entries each time a host is added or removed.

I suspect the point of the exercise is to define 4 logical subnets on one physical interface on the router to implement the 4 logical subnets on the one physical network - not a difficult problem at all once you get past the point of understanding TCP/IP is a 'logical' communications protocol and you can have multiple logical networks residing on one physical network - just define 4 logical networks with the IP range and netmask on the physical interface connected to the switch the servers connect to. You do not need to do anything to the switch (unless you are using one of the newer switches capable of layer-3 switching [routing] like a Cisco 3750 series or such) as most inexpensive switches are layer-2 devices and use MAC to determine the destination port to send the packet destined to a specific device on the physical network.

This works by virtue of the fact the router will perform the IP to MAC translations for the host destination and send the packet destined to a specific host on the physical network to the specific MAC address for the host. Since the switch already 'knows' the MAC address of the devices on the physical network it will send the packet to the specific port the host is connected to.

Hope this helps...

gm...

well i guess that's the angle, but if phrases like "interior gateway protocol" and ospf are being used, presumably ther's more to it we're not aware of?

I think someone was making the assignment more difficult than it really was from what I read...

gm...

The assignment is exactly as what i told,, and ya,, if i statically define all the switches ip to the router, there is indeed no need for IGPs.

THANX guys,, thanx very much.