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Old July 20th, 2018, 11:39 AM   #1
Iandm
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2 Stratix 5700 and Dchp

Im trying to have 2 5700s connected and utilize Dchp on both switches. I do not know if its possible with the Lan-light version(routing template not found). Any tips are appreciated. Ive tried enabling snooping and reserved on both switches.
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Old July 20th, 2018, 01:11 PM   #2
keshik
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Why would you want multiple DHCP devices on a single network?
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Old July 20th, 2018, 01:43 PM   #3
Iandm
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im using dhcp persistence so static ip assignment. theres 8 ports on one switch and 8 on another so a total of 16 assigned ips. switch 1 is 172.21.50.10 and 2 172.21.50.11
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Old July 21st, 2018, 07:52 PM   #4
brendan.buchan
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It is bad practice to have multiple switches acting as DHCP servers on a single network.

Just set up one switch to be the DHCP server and as long as both switches are connected it will be able to hand out addresses for all devices across the network.
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Old July 22nd, 2018, 11:46 AM   #5
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Brendan, could you explain why this is bad practice?

We have a similar setup to what the OP is asking about. PLC controller(L72 CLX) is in a cabinet on first floor with its own 5700 stratix, and another cabinet on the second floor (same system) with a 5700. Both switches on the same subnet, each has its own static IP and its own IP pool for DHCP persistence.
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Old July 22nd, 2018, 06:18 PM   #6
brendan.buchan
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In very specific situations having multiple DHCP servers on a single network may be a reasonable solution but in general it is bad practice.

The reason being that when a device connects to the network and requests an IP address via DHCP, it is basically a race to see which DHCP server can respond fastest to this request and assign it an IP address. There is no certainty to whether it will get an IP address from DHCP server 1 or DHCP server 2.

Further to this, unless you separate the IP address pools then you can also end up with duplicate IP addresses as DHCP server 1 doesn't know that DHCP server 2 may already have assigned a device to a specific IP address already.

In general I dislike DHCP for industrial networks. In my opinion it is a better solution to have everything on static IP's.
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Old July 23rd, 2018, 06:13 AM   #7
Iandm
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I guess its still not clear. I'm using static IP assignments on both but when connecting the switches together, my port assignments are not working as they should. I'm just trying to find out if routing needs to be enabled with separate Vlans to use DHCP Persistence(Static Ips) on multiple switches.
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Old July 23rd, 2018, 07:40 AM   #8
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Quote:
Originally Posted by Iandm View Post
I guess its still not clear. I'm using static IP assignments on both but when connecting the switches together, my port assignments are not working as they should. I'm just trying to find out if routing needs to be enabled with separate Vlans to use DHCP Persistence(Static Ips) on multiple switches.
Are your VLAN Id's different on each switch? We use DHCP persistence and per port. If all devices on the same subnet, then no routing should be necessary. On the one above, our VLAN ID's are the same, but the IP pools are different. EX - first floor uses .10-19 and second floor uses .20-.29 . We use the 'lite' version of the 5700 also.
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Old July 23rd, 2018, 10:00 AM   #9
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im getting close. all on vlan 1. I think my problem was not being patient enough and using my network adapter to identify ip address rather than Rslinx or mac scanner. Im interning and couldnt get it downloaded :/.
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Old July 23rd, 2018, 03:45 PM   #10
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Brendan

Stratix switches uses DHCP persistence per port. This means that each port is assigned an IP address so it wouldn't be possible to have duplicate IP addresses, and would also not be possible for only one of the two switches to be configured for DHCP and assign addresses to other switches ports or device.
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Old July 23rd, 2018, 03:52 PM   #11
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Ive got it working as of now. Id like to isolate my devices(8 E300 overloads on each switch) Port 9 on both are connected together and port 10 for laptop to access it all. Wouldnt a vlan for each port make since if i dont want devices talking together?. i try setting up on port on vlan but lose access to it from my 4 trunk ports 9 10 on both swtiches
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Old July 23rd, 2018, 08:45 PM   #12
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Quote:
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Brendan

Stratix switches uses DHCP persistence per port. This means that each port is assigned an IP address so it wouldn't be possible to have duplicate IP addresses, and would also not be possible for only one of the two switches to be configured for DHCP and assign addresses to other switches ports or device.
Yep, my bad. What I stated above was in reference for generic network-wide DHCP. I didn't realise the OP meant DHCP persistence per-port.

Sorry guys!
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