Re: DHCP failure, but everything *seems* correct?

tjdunn1980 · ‎04-06-2023

Hi, I'm teaching a class some basics of Cisco configuration and I'm in a bit of a pickle. According to our materials the configuration I'm using should be functional, but not even the skills team who created the **bleep** exercise can tell me what's going wrong. Everything appears to be configured correctly in our simulated network (router, switch, WAP, server w/ dhcp and dns, pcs and laptops), yet nothing is pulling the right Ip configuration. Some aren't getting DHCP at all, others are getting addresses outside the scope...

I've gone over the simulation a dozen times, rebuilt it from scratch, worked from the same commands and processes I use in the real world... but it's just not working. I can't for the life of me figure out where I've gone wrong. I think stress is getting to me, I need fresh eyes and right now it seems a bunch of strangers on the internet are my only option.

Please take a look at this Packet Tracer file, tell me if you can see where I've gone wrong.

Passwords for devices are:

Router Enable: EnPa55R
Router Console: ConPa55R
Switch Enable: EnPa55sW
Switch Console: ConPa55sW

David Ruess · ‎04-06-2023

Hello,

Can you provide a bit more detail of what is "supposed" to look like. I was able to pull an IP address on the PCs and the printer is configured for static IP assignment.

-David

tjdunnau · ‎04-07-2023

Gateway: 192.168.100.1
DHCP, DNS server: 192.168.100.2
DHCP pool start: 192.168.100.11
WAP: 192.168.100.3
PCs and Laptops: DHCP

When I run it, the PCs either pull IPs from 192.168.100.5-9 (outside DHCP scope) or fail and just have a link-local address. Laptops just fail completely.

Martin L · ‎04-07-2023

outside of scope issue is because of 2 pools in your DHCP server; There is always default pool which u cannot delete but u can rename and make changes; then, you can add new one on different subnet if u need one. With 2 pools, I got correct IP after renewal, (see pic)

The DHCP failed. APIPA is used means that your PC booted before switch could change ports from block to active/forwarding; this is where your spanning tree portfast default (and rapid stp) comes handy.

C:\>ipconfig /renew

IP Address......................: 192.168.100.11

Subnet Mask.....................: 255.255.255.0

Default Gateway.................: 192.168.100.1

DNS Server......................: 192.168.100.2

Regards, ML
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tjdunnau · ‎04-07-2023

I went and deleted the custom pool and entered the needed IP info in the default one. It wouldn't let me rename it though - but that's a minor issue, I can note that in my official feedback to the students as a "reasonable adjustment" so any auditors know they didn't get that part wrong.

The laptops were still failing. I went back and had a look at the marking file to compare. Everything looked fin in the WAP configuration. Then I realised something; I've been working with the port labels off because they look cluttered, and I've already configured everything correctly so why do I need them, right? Yeah, you can probably imagine how red my face is right now... the WAP was connected on the wrong port. It was linked to the switch on the Internet port instead of the first fast ethernet. The second I moved that cable, the laptops were working.

It was a rookie mistake, but I wouldn't have noticed it if you and the others weren't helping me troubleshoot.

Thank you!

Martin L · ‎04-07-2023

For DHCP issue : there are 2 pools on DHCP server and one is missing gateway and DNS IPs; PCs get IP but without gateway and DNS IP. Once I add info and did ipconfig /renew on PCs, I got ping OK; Also, To make sure PCs can get IPs, add portfast default on switch and run Rapid STP.

Picture shows some pings OK and laptop connected

Wireless router is not broadcasting SSID to laptops and security is not set up on those laptops. I enable SSID B-cast and disable security, then went to Laptops and connected them to BranchTF. They were ok and laptop can ping PC. Obviously you need security to be on and to match laptop settings to wireless router. There should be some samples in PT with wireless setups

Regards, ML
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tjdunnau · ‎04-07-2023

I'm not sure why those laptops weren't configured - I thought I'd saved the file with them set up. SSID broadcast is supposed to be disabled, and manually configured on the laptops with WPA2-PSK, AES. They're connecting, they're pinging (IP only, not FQDNs). They're just not pulling DHCP info.

Enabling RSTP and portfast default didn't make any difference for my copy of the file. Still the same error - PCs pulling from outside of DHCP scope, laptops not pulling IPs at all.

Martin L · ‎04-07-2023

in case of wireless, once u connect to wireless router, make sure his DHCP is on (which it was). Look at GUI page of router under Setup and Network setup. make sure save any changes (scroll down and save). if u have SSID broadcast disabled, then u must manually set laptops up to connect to your wireless network using hidden SSID. all those can be set up on main Config tab of laptop under wireless0 (next to bluetooth).

Regards, ML
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tjdunnau · ‎04-07-2023

Forgot to mention: One pool is a default that PT won't let me delete or edit. The other (BranchPool) is the "real" one. As far as I can see, it has the gateway (192.168.100.1) and DNS (itself, 192.168.100.2) correctly configured.

Martin L · ‎04-07-2023

There are some issues when pinging 8.8.8.8. Looks like we have a ~~loop~~

Update: not a loop but ACL blocking which is good. But u need to setup NAT,

C:\>ping 8.8.8.8

Pinging 8.8.8.8 with 32 bytes of data:

Reply from 203.165.200.1: Destination host unreachable.

Ping statistics for 8.8.8.8:

Packets: Sent = 4, Received = 0, Lost = 4 (100% loss),

Regards, ML
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tjdunnau · ‎04-07-2023

I had setup nat, using the following:

Set up ACL:

BranchR(config)# ip access-list standard BRANCH_OFFICE_LAN_To_INTERNET
BranchR(config-std-nacl)# permit 192.168.100.0 0.0.0.255
BranchR(config-std-nacl)# exit

Set up NAT:

BranchR(config)# int g0/0/0
BranchR(config-if)# ip nat outside
BranchR(config)# int g0/0/1
BranchR(config-if)# ip nat inside
BranchR(config)# ip nat inside source list BRANCHTF_LAN_To_INTERNET interface g0/0/0 overload