Simplest network imagineable doesn't work!!

thefear78

Hello all!

I have built a network consisting of one Cisco 2611 running IOS 12.0 and two XP machines.
The config for the fastethernet is as follows

Fastethernet 0/0 172.16.10.1 255.255.255.0 ----> Host 1 172.16.10.2 255.255.255.0
Fastethernet 0/1 172.16.20.1 255.255.255.0 ----> Host 2 172.16.20.2 255.255.255.0


Can ping interface of host 1 from router interface e0/0 (and vice versa)
Can ping e0/1 from Host 2 but not vice versa!!

Can't ping host to host even though they're directly connected interfaces and

router(config)#show arp
&
router(config)#show ip route

lists all four hardware addresses in this network and their corresponding ip addresses!!

I built this network following an example from the Sybex CCNA book, disabled my firewalls and did a erase startup-config to be sure I had a clean slate... am I missing something completely mundane here?

I write the CCENT in a week and this has me feeling like a dummy!

Daniel333

Can you get us a show run?

thefear78

Must have been the netmask as when I switched the config to a class C 192.168.1.1 /25 network on both interfaces it works and I have total connectivity.

The way I understood things tho I should be able to ping any private ip that is directly connected? Is this not right?

arthell

You're right, it was the mask.

Those two networks you listed were in different subnets. 172.16.10.1 with a mask of 255.255.255.0 gives you a network with addresses 172.16.10.1 -> 172.16.10.254. Anything outside that 172.16.10.x range will be 'invisible' to computers inside that range, and vice-versa.

Even though the ports are on the same router doesn't necessarily mean they will all interact with each other - it depends on how you config them, namely the subnetting.

freetech

You can only ping an interface that is either correctly routed or on the same subnet. Ping is L3 protocol that needs that routing table or correct subnetting. You can "show CDP neighbors" to verify connectivity at L2 and get other info, regardless of the IP address, but you need to be in the same subnet to ping.

thefear78

I cannot directly connect two hosts to two different fastethernet ports on a router?

I try on the same subnet and I get an overlap error and on two seperate subs there is no connectivity.

So the hosts need to be attatched to a switch or hub and then into an ethernet port to talk to each other?

bighornsheep

thefear78 wrote:

Fastethernet 0/0 172.16.10.1 255.255.255.0 ----> Host 1 172.16.10.2 255.255.255.0
Fastethernet 0/1 172.16.20.1 255.255.255.0 ----> Host 2 172.16.20.2 255.255.255.0

This setup is PERFECTLY fine, the masks are fine, your IOS should have "ip classless" as the default, but you can be sure of it if you issue that in global config mode.

Router>en
Router#config t
Router(config)#ip classless

On Host 1, make sure you have 172.16.10.1 set as the default gateway
On Host 2, make sure you have 172.16.20.1 set as the default gateway

I am not sure if it's what you're doing, but you CAN NOT have more than one default gateway in WinXP, so if there's already another NIC on those winxp machines that's receiving a DG from DHCP on your broadband router/WAN internet access, you should disable those NIC while you're doing the cisco labs.

Now in exec mode, if you issue sh ip route, you should see something like:
C 172.16.10.0/24 is directly connected, Fastethernet 0/0
C 172.16.20.0/24 is directly connected, Fastethernet 0/1

Now you should have full layer 3 connectivity and all IP addresses should be pingable.

If you want to troubleshoot, you can also issue sh ip int brief in exec mode to check that the status and protocol are "UP" for each of those interfaces.

thefear78 wrote:

I cannot directly connect two hosts to two different fastethernet ports on a router?

Router directly to host requires a cross-over cable.

thefear78

Yes, it was my DG's I had misconfigured! Now have end to end connectivity, thanks!