In our network topology , we 've two windows DHCP server. So we use "ip helper" command for relaying;
ip address 10.50.11.252 255.255.255.0
ip helper-address 10.50.10.10
ip helper-address 10.50.10.11
no ip redirects
no ip proxy-arp
ip wccp 0 redirect in
ip wccp 70 redirect in
standby delay minimum 180
standby 11 ip 10.50.11.254
standby 11 timers msec 500 2
standby 11 priority 150
standby 11 preempt
standby 11 track 1 decrement 35
I've two question ;
1 ) Is "ip helper" command provide check of DHCP service availabilitiy on servers ?
2) A few days ago, our first dhcp server (10.50.10.10) service (not machine) went down, but client couldnt requested ip from secondary dhcp. So how could we do redundacy when we face similar issue ?
Best regards, Thanks
1) the dhcp relay helps to forward dhcp bootp broadcasts to a dhcp server residing on a diferrent network separated by a l3 device such as a switch/router as by default broadcast are prohibited to traverse a router.
2) when you say service was the primary helper addrees still available and also is the secondary helper addreess reachable?
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I mean, server is up but DHCP service stopped mode for maintenance. Secondary was reacheble.
Also scope on two server running without overlapping. Network range is same but we use excluded ip range feature.
Having the following configuration:
ip helper-address 220.127.116.11
ip helper-address 18.104.22.168
This will configure DHCP relay in the router. It receives a broadcast DHCP request and converts it into a unicast message directed exclusivly to both DHCP servers.
The router "sees" the DHCPDISCOVER packet and forwards it to bothaddresses simultaneously. Then, both DHCP servers will make an offer (DHCPOFFER), if they are up and received the request.
The client will receive each offer at one time, one first then the other. if it finds the offer agreeable, itwill send another broadcast, a DHCPREQUEST, specifically requestingthose particular IP parameters. Why does the client broadcast therequest instead of unicasting it to the server? A broadcast is usedbecause the first message, the DHCPDISCOVER, may have reached more thanone DHCP server. If more than one server makes an offer, thebroadcasted DHCPREQUEST allows the other servers to know which offerwas accepted. The offer accepted is usually the first offer received.
Sometimes, in other to make one server responde faster then the other, you can configure the delay of response in the DHCP server.Also, for sincronization between DCHP server, either they support this feature or you will have to have your subnet divided betweenthe 2 servers without overlapping.
According to this informations, our clients should have request ip over second one and took ip address.
Have u any idea regarding our issue ? What we supposed to do ?
Is the second ip helper-address reachable?
Also are both dhcp scopes enabled and authorised in dhcp on Both servers?
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Unfortunately i couldnt test it now because of windows 2012 upgrade processes. But my colleagues told me it was authorised and reachable status at issue date.
After completing upgrade, i'm going to test again and inform you regarding to case.