dhcp snooping between switches

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nsotis28
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Joined: 03 Sep 2019 08:50

dhcp snooping between switches

Post by nsotis28 » 06 Sep 2019 09:37

Dear all ,

I need your assistance to configure snooping between 6450 and 6350.
These switches are connected via 2 physical ports with link aggregation enabled.Configuration is as follows

6450 - ip helper dhcp-snooping enable
ip helper dhcp-snooping port 1/4 trust ( DHCP server)
ip helper dhcp-snooping linkagg 14 trust ( uplink la group)

6350 - ip helper dhcp-snooping enable
ip helper dhcp-snooping linkagg 14 trust ( uplink la group)

Clients on 6450 receive ip address but clients on 6350 no. Using wire-shark i see that DISCOVER packet never pass from 6350 to 6450.

Can you pls asvice ?

silvio
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Re: dhcp snooping between switches

Post by silvio » 09 Sep 2019 14:50

You config is correct for L2 (at 6450 the trust of lag is not necessary). But if the dhcp server is connected in an other vlan than your clients, than you need "ip helper dhcp-snooping vlan xxx". xxx is your client-vlan.

nsotis28
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Joined: 03 Sep 2019 08:50

Re: dhcp snooping between switches

Post by nsotis28 » 11 Sep 2019 01:03

Hi Silvio,

Thank you for your reply.
DHCP is on the same VLAN so we are talking about L2 config.Disabling trust on 6450 has no affect.
I want to mention that both switches have ip helper configured but for another vlan that i use for guest computers.

Do you think that this is relevant with my problem?

silvio
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Re: dhcp snooping between switches

Post by silvio » 12 Sep 2019 04:10

Yes possible.
you should config all the ip-helper per-vlan and the dhcp-snooping for the other vlan.
Update both your switches to the newest release (there where snooping problems with older releases).
regards
Silvio

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