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DHCP Relay on EX4600 not working when DHCP server is not routed in EX4600 device

‎12-12-2019 11:05 PM

Hello all!

I have a problem when trying to migrate DHCP server. We're moving our DHCP server to a new datacenter from our office, when doing this we noticed that our EX4600-40F which acts as router for our office wont forward dhcp relay requests to the new DHCP server at all.


And when adding traceoptions it wont log any failures either.
Our office DHCP server has IP: 192.168.98.5 (irb.98)

Our new DHCP server in DC has IP: 10.101.0.6

Client network at office: 192.168.100.0/23 (irb.100)

Config at the office (working configuration):

markus@core-sw01# run show configuration forwarding-options dhcp-relay
forward-snooped-clients all-interfaces;
overrides {
    allow-snooped-clients;
    layer2-unicast-replies;
    trust-option-82;
}
relay-option-82;
server-group {
    DHCP-SERVERS {
        192.168.98.5;
    }
}
active-server-group DHCP-SERVERS;
group DHCP-RELAY {
    interface irb.100;
}
markus@core-sw01# run show route 10.101.0.0

inet.0: 165 destinations, 172 routes (165 active, 0 holddown, 0 hidden)
+ = Active Route, - = Last Active, * = Both

10.101.0.0/23      *[BGP/170] 6w2d 13:52:44, localpref 100
                      AS path: 64512 I, validation-state: unverified
                    > to 10.100.0.16 via irb.3051
markus@core-sw01# run show configuration interfaces lo0
unit 0 {
    family inet {
        address 10.100.0.7/32;
    }
    family inet6 {
        address 2a0e:bb80:1001::1/128;
    }
}

Ping from core-sw01 (EX4600-40F) to DC DHCP-server:

markus@core-sw01# run ping 10.101.0.6 source 192.168.100.1
PING 10.101.0.6 (10.101.0.6): 56 data bytes
64 bytes from 10.101.0.6: icmp_seq=0 ttl=63 time=0.648 ms
64 bytes from 10.101.0.6: icmp_seq=1 ttl=63 time=11.355 ms
^C
--- 10.101.0.6 ping statistics ---
2 packets transmitted, 2 packets received, 0% packet loss
round-trip min/avg/max/stddev = 0.648/6.002/11.355/5.354 ms

markus@core-sw01# run ping 10.101.0.6 source 192.168.98.1
PING 10.101.0.6 (10.101.0.6): 56 data bytes
64 bytes from 10.101.0.6: icmp_seq=0 ttl=63 time=0.702 ms
^C
--- 10.101.0.6 ping statistics ---
1 packets transmitted, 1 packets received, 0% packet loss
round-trip min/avg/max/stddev = 0.702/0.702/0.702/0.000 m


Relay works fine within the switch even when it's done over l3-interfaces (server on irb.98 and clients on irb.100). Relay does not work when DHCP-server is not routed in switch.

 

Any clues on why it's like this?

6 REPLIES 6
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Ethernet Switching

Re: DHCP Relay on EX4600 not working when DHCP server is not routed in EX4600 device

[ Edited ]
‎01-20-2020 04:58 PM

We had the exact same issue. We were running Junos 17.3R3-S3.3 on our stack of EX4600s and DHCP was working fine. We run a Windows based DHCP server and use the EX4600 to relay DHCP packets. We upgraded to Junos 18.1R3-S6.1 and DHCP stopped working. J-Tac pointed me to this PR which states the problem

https://prsearch.juniper.net/InfoCenter/index?page=prcontent&id=PR1396470

 

The issue was Junos 18.1R3-S6.1 was the J-Tac recommended version at the time we did the upgrade (Nov. 9, 2019) even though it had this DHCP bug. We rolled back to Junos 17.3R3-S3.3 and everything was working again. On 12-15-2019 we decided to try the upgrade again and went to Junos 18.4R2-S2 which is still one of two J-Tac recommended versions for the EX4600. We once again had a DHCP issue and rolled back to 17.3R3-S3.3.

 

We thought about trying Junos 18.1R3-S8 which is the other recommended version but am concerned we will have this problem again. Did you solve this issue? What version of Junos are you running?

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Re: DHCP Relay on EX4600 not working when DHCP server is not routed in EX4600 device

‎01-20-2020 05:52 PM

Here is how we have DHCP relay setup and as I stated in my previous post this works fine with Junos 17.3R3-S3.3 but has not worked when upgrading to other J-Tac recommended versions

 

    dhcp-relay {

        server-group {

            DHCP-Servers {

                10.121.125.100;

                10.121.125.101;

            }

        }

        active-server-group DHCP-Servers;

        group DHCP-Servers {

            interface irb.8;

            interface irb.28;

            interface irb.32;

            interface irb.36;

            interface irb.40;

            interface irb.44;

            interface irb.48;

            interface irb.52;

            interface irb.56;

            interface irb.57;

            interface irb.58;

            interface irb.59;

            interface irb.60;

            interface irb.61;

            interface irb.144;

            interface irb.148;

            interface irb.152;

            interface irb.156;

            interface irb.160;

            interface irb.164;

            interface irb.200;

            interface irb.208;

            interface irb.216;

            interface irb.224;

            interface irb.232;

            interface irb.240;

            interface irb.242;

        }

    }

}

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Re: DHCP Relay on EX4600 not working when DHCP server is not routed in EX4600 device

‎01-21-2020 06:39 AM

To those of you experiencing this situation, could you please respond with Case #'s, not PR #s.

 

Thanks

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Re: DHCP Relay on EX4600 not working when DHCP server is not routed in EX4600 device

‎01-21-2020 08:20 AM

When we upgrade from Junos 17.3R3-S3.3 to Junos 18.1R3-S6.1 and DHCP stopped working I opened case number 2019-1109-0121

When we upgraded from Junos 17.3R3-S3.3 to Junos 18.4R2-S2 and DHCP still had issues I opened case number 2019-1215-0006

 

Is this applicable where perhaps we have DHCP relay configured incorrectly? I posted our DHCP config earlier

https://forums.juniper.net/t5/Ethernet-Switching/DHCP-Relay-EX4600-with-Routing-Instances/td-p/31991...

Ethernet Switching

Re: DHCP Relay on EX4600 not working when DHCP server is not routed in EX4600 device

‎01-21-2020 03:15 PM

@HendersonD - my research also only found PR1396470 which should have been fixed in 18.4R2, which would include 18.4R2-S2 you tried, unless S1 or S2 created issue again.  Same fix is in 18.1R3-S8 (not S6), which may be worth trying.  If this code works, then likely 18.4R2-S1 or S2 created the new issues you saw.

 

Best I can come up with.  If possible, I would try 18.1R3-S8 and regardless of outcome, open a new case with TAC to report your findings.

 

Good luck

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Re: DHCP Relay on EX4600 not working when DHCP server is not routed in EX4600 device

‎03-14-2020 06:12 AM

This morning we upgraded this stack to Junos 18.1R3-S9.1 which is one of the current JTac recommended versions. I am happy to report that the upgrade went fine. DHCP is working as it should. After two failed upgrades described in earlier posts, I guess the 3rd time is the charm

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