Extreme bootprelay question....

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  • Updated 4 years ago
The LAN router (say a MLS 7i) recvs a DHCP request from a downstream client.
The DHCP server is directly off the LAN router in the same subnet as the LAN router.
Now ALSO if the bootprelay statement is also configured with the IP Address of the DHCP server,....what happens to
the DHCP request? 

Does it come into the LAN router (really MLS), and as a broadcast gets broadcast out all ports of the 7i minues the port it came in on (switched port)....then does it also get sent via routing to the same IP via the bootprelay statement....how would the 7i handle this order of precedence?
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Jimmy

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Posted 4 years ago

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Sathish Arul, Alum

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Hi Jimmy,

Considering this as a common question for bootbrelay for all Platform switch.

It will broadcast DHCP request to all ports other then the one from which it receives.

Though we configure a bootprelay statement - still the DHCP server IP mentioned here belongs to same subnet, so switch will look at the DHCP server IP mentioned and it concludes that DHCP server IP belongs to local subnet it simply discards as already the same requests have been broadcasted.

Bootprelay will be used when DHCP servers are placed in a different subnet in that case, switch will look in to the next hop i.e DHCP server IP - it may be learned as directly connected or from any routing protocol. Then that DHCP requests will be forwarded to that next hop - keeping local vlan's interface IP as the source & DHCP server IP as the destination.

But when DHCP server placed in local subnet then DHCP reques source would be always 0.0.0.0.