Ethernet Switching
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Juniper EX DHCP Relay

‎10-13-2018 12:42 PM

Hello,

 

I am trying to get DHCP relay to work with multiple subnets on an EX4200 switch.  

 

set interfaces vlan unit 12 family inet address 192.16.108/25 primary
set interfaces vlan unit 12 family inet address 172.22.18.1/26
set interfaces vlan unit 12 family inet address 192.16.110.129/26


set forwarding-options helpers bootp interface vlan.12 server 192.168.108.101
set forwarding-options helpers bootp interface vlan.12 server 192.168.108.102

 

DHCP works, but once all the IP's in the 192.16.108/25 range get used, it does not start dishing out from the next range like it does with Cisco.  What am I missing?

 

Also, these IP' were edited.   In real life network they are public ip addresses, and so I can not simply just create a larger subnet. 

 

Thanks!

 

 

 

 

 

3 REPLIES 3
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Ethernet Switching

Re: Juniper EX DHCP Relay

‎10-13-2018 05:29 PM

problem not in ex42, because in case of dhcp relay ip addresses served from dhcp server, and you should have configured linked pool on dhcp server so when first pool in exhausted it should start allocate ip addresses from second pool.  Which dhcp server do you use ? 

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Re: Juniper EX DHCP Relay

‎10-13-2018 10:26 PM

I started going down that path, but I can not find any documentation on that for ISC dhcp server.

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Re: Juniper EX DHCP Relay

‎10-14-2018 12:21 AM

Hello,

 

First things first -  You are not using DHCP relay, You are using BOOTP helper. The difference is that JUNOS BOOTP helper is stateless/does not keep track of forwarded requests whereas JUNOS DHCP relay does.

Secondly, if I understand the scenario correctly, when 192.16.108/25 subnet is exhausted, then DHCP server does not dish out IPs for next subnet (be it 172.22.18.1/26 or 192.16.110.129/26)?

If yes then the problem is likely that EX4200 always uses an IP from 192.16.108/25 subnet as giaddr and Your DHCP server looks for giaddr to select a pool. Please add following knob to force EX4200 using secondary IPs as giaddr, re-test and report back:

 

set forwarding-options helpers bootp interface vlan.12 apply-secondary-as-giaddr

https://www.juniper.net/documentation/en_US/junos/topics/reference/configuration-statement/smart-rel...

HTH

Thx
Alex

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