Issues with switch configuration

chrisse · ‎07-01-2022

Hello,

I have set up my new home WIFI a few months ago and I have some issues I am unable to get hold of... maybe somebody can help, I think there is something missing which I just don't get...

My hardware components:

I have a modem provided by my ISP. It does have WLAN and can be used as DHCP Server, but I have turned both services off (the WLAN is not good enough to cover our whole house).
I have a Cisco SG350-10MP 10-Port Gigabit PoE Managed Switch. It's linked to the ISP modem with a LAN cable.
I have 2 Cisco Meraki Access Points, which in turn are linked to the Switch via LAN cables. The Access points broadcast a few different WIFI networks, mainly because I want to provide different networks for different users, i.e. guest users have their own WIFI not being able to use i.e. printer and the like.

My idea:

I want to use the Cisco switch as a central component. It should do the DHCP and all the IP address assignment. Why? Because I am unsure how long I will stay with my ISP, might change it and I think that the Cisco switch is the central component which will remain for the years to come.
I want to use static IP addresses for a few devices (i.e. printer) but generally DHCP for all end user devices.
The devices with static IP addresses should be reachable from the different WIFI networks I am broadcasting.
Since I have a central switch, I can power off my Access Points i.e. during the night. Nice feature.

My configuration:

As I have stated, I have given static IP addresses to my ISP's modem, to my Access Points, to my printer.
ISP modem does not broadcast a WIFI, does not serve as DHCP. It has the static IP address set, which is also used on the switch.
On my Cisco switch I have created a Network pool, assigned some IP address range and network mask. I have set the ISP's modem address as Default Router IP Address and the DNS Server IP Address.
All end user devices are using DHCP. There are considerably more IP addresses than devices, approximately 3 times as much IP addresses than devices.
My access points are set up to use bridge mode.
Usually, when connecting to the network I receive a new IP address from my pool (plus the rest of the DHCP information) and can start using the device.
I have saved my Switch config as running configuration, did a backup and also set it as startup configuration.

My issue:

However, we have had a power outage a few times in the last year (some electrical device obviously had some issues) and the switch was shutting down. After the restart, all devices have been unable to get a IPv4 address, however, on my Laptop I could see that I get an IPv6 address (although this is not specifically configured).
When I then assign a static IP address to my computer (from the network pool) I am able to connect to the Switch configuration. Usually, after clicking around and not changing anything specific, all of a sudden the IP addresses would get assigned again to all devices and the network works again.
However, this does only happen after connecting to the switch management page and unspecifically clicking around (at least I cannot recall changing anything specific).
1-2 weeks ago I have recognized that one of my broadcast WIFI network seems to be working (assigns IP addresses) although the other WIFI networks are not assigning IP addresses. I discovered that for that specific network I have not set "bridge mode", but "NAT mode".
I have then tried to set "NAT mode" for all my networks and it appears as if the whole WIFI network is working considerably better now (devices are now able to connect without issues even after a power outage).
However, the IP addresses are now assigned (I assume) by the access points and not by the DHCP of the Cisco switch. Also, communication with my printer is hardly possible (even though I have enabled the option on the access point, that devices can connect to each other in NAT mode).

Now I am pretty unsure what to do. I do not like my access points assigning IP addresses, because I have had the idea of managing them centrally, at some point maybe being able to have certain rules for my children's devices (assigning static IP's to their devices and blocking them from certain websites, ...). However, if I go back to the previous setting (bridge mode on the access points) I again face the issue that the network will not work for some reason after a power outage... Did anybody experience something similar and can provide help? Any hint is much appreciated!

Georg Pauwen · ‎07-01-2022

Hello,

chances are that stopping and restarting the DHCP service on the switch when the switch comes back up resolves the issue.

Configure the EEM script below:

event manager applet DHCP_SERVICE
event timer cron cron-entry "@reboot"
action 1.0 cli command "enable"
action 2.0 cli command "conf t"
action 3.0 cli command "no service dhcp"
action 4.0 cli command "service dhcp"
acyion 5.0 cli command "end"

chrisse · ‎07-02-2022

Hi Georg,

many thanks for your suggestion. I just wanted to try it out, but was wondering - you thought I should execute the script in the CLI of the switch? Because I have only used the GUI so far, but I guess there is no way to make the settings via GUI, right?

Thanks,

chrisse

Georg Pauwen · ‎07-02-2022

Hello,

very good question actually. I don't think the GUI lets you do that. The CLI is fairly easy once you get used to it.

chrisse · ‎07-03-2022

Hi Georg,

no problem, I am going to try the solution you have stated anyway. Maybe it is able to solve the issues we have.

One more thing which strikes me: I just did some setup of a new device and the network was not having a power outage today. I have previously operated the relevant WIFI network it in NAT mode, then I have switched to "bridge" mode just before connecting the device I have set up. After 3-4 tries the device was still not able to get an IP address (in bridge mode). After switching back to NAT mode, it worked within 30 seconds and I had an IP address.

This appears a bit odd to me, since I guess your approach would only fix an issue connected to restarts of the switch, right? Somehow it appears as if IP addresses are just not (always?) handed out to my devices...

Georg Pauwen · ‎07-03-2022

Hello,

what AP do you have ? And what 'device' are we talking about ? Do you have a schematic drawing of your topology that shows how the AP, switch, and (I assume) ISP modem/router are connected ?

chrisse · ‎07-04-2022

Hi Georg,

of course - here is a schematic drawing:
[image: image.png]
The IP Address pool on my Cisco switch is configured to assign IP's from
192.168.1.1 to 192.168.1.49 (lease is infinite, but as I have said, I am
not running out of ip addresses and I have already tried to set a time
limit to that). Network mask is 255.255.255.0 and DNS and Standard Gateway
192.168.1.1.

All lines are standard LAN cables, just the ISP Modem is connected to the
internet via LTE. The device I was trying to connect to the internet was a
Lenovo Tablet. However, I have the same issue (hardly not getting an IP
address) on my wife's Samsung mobile phone as well plus sometimes on our
Amazon Echo devices.

The access point I have is 2x the same Cisco Meraki Go GR10.

Thanks!

PS: Maybe I should note that I have absolutely no problem in getting an IPv6 address, or whatever reason. I have not set it up explicitly on the DHCP server. However, I always get an IPv6, but as I have said the IPv4 address is missing.

chrisse · ‎07-04-2022

I have just done some more tests after a power outage today. It appears as if it really is related to the DHCP server. When I just go to "Edit" mode of my address pool and hit "apply" (without changing anything) things seem to start working again normally.

Georg, does the script you have provided only restart DHCP in case of explicit (user-triggered) reboots? Or at any reboot?

Thanks!