DHCP helper/relay assistance


Hi guys, I'm new here so this is all new and exciting. I am a rookie network admin learning the ropes at my job and have a question. We have 2 Black Diamonds. Do each need to have the same DHCP address for bootprelay? For example BD1 has 192.168.1.1, 192.168.1.2 and BD2 has 192.168.1.1 and 192.168.1.3.I figure it's for redundancy but does this cause an issue?

5 replies

Userlevel 6
Hello David,

Welcome to the HUB!

If you are referring to putting an IP on a VLAN then they need to be different. protocols like bootprelay work on top of an already routing network. Each switch needs to be able to logically reach the DHCP server in order for bootprelay to work properly.
Userlevel 7
It sounds like maybe your two cores are using VRRP, which is why you have the .1 IP on each of them.

For BOOTP, you'll want to set the same IP address of the DHCP/BOOTP server on the two cores. For example, my two cores in the lab have this same configuration line on them:
code:
configure bootprelay add 10.x.x.x vr VR-Default

This way, either core receiving the DHCP Request knows to send it to the server VLAN so the DHCP server can respond.
Hi Patrick! You've actually helped me out in the past with service orders and other questions when I've called in!

Pardon my newbness, so each Black Diamond should have different booprelay addresses of DHCP servers? I see that there is a limit of 4 entries allowed. I added an entry on BD2 of a DHCP on another subnet but couldn't add it to BD1 as it already had reached the entry limit.
I hope this makes sense. Maybe I need to do more reading.
Userlevel 6
Hello David,

I think I misunderstood your description. The switches can have the same DHCP server configured in bootprelay as Drew mentioned. I thought you were talking about the underlying IP addresses on the switch.
Awesome, thank you guys for the info! I want to slowly take my time and try to clean up our network environment.

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