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Webcast-Catalyst9k
New Member

Interface with 2 Subnets

What is the process of putting 2 Ip subnets on interface.

172.16.0.0 255.255.0.0

&

172.30.1.0 255.255.255.0

Or is it even possible?

Thanks in advance

5 REPLIES
Silver

Re: Interface with 2 Subnets

Dear Miller,

Yes it is possible,

U can create subinterface and can assign ip from each subnet to each interface or u can even have one ip as primary and other as secondary.

Rgs,

New Member

Re: Interface with 2 Subnets

What are the steps for secondary IP address?

Thanks for your response.

New Member

Re: Interface with 2 Subnets

Never mind i figured it out

ip address 172.30.1.1 255.255.255.0 secondary

is there anything i need to watch out for?

Silver

Re: Interface with 2 Subnets

hi,

Nothing required. You can use the same.

ip address ip-address mask [secondary]

no ip address ip-address mask [secondary]

ip-address IP address.

mask Mask for the associated IP subnet.

secondary (Optional) Specifies that the configured address is a secondary IP address. If this keyword is omitted, the configured address is the primary IP address.

Rate if it does,

Rgs,

Hall of Fame Super Gold

Re: Interface with 2 Subnets

Tim

There are a few things to keep in mind when you configure a secondary address on an interface:

- any packet originated by the router (routing update, syslog, snmp, etc) and sent out that interface will use the primary address as the source address and not the secondary.

- if you run a dynamic routing protocol that establishes neighbor relationships (EIGRP, OSPF) they will form neighbor relationships on the primary address and not on the secondary address. (the dynamic routing protocol can advertise the secondary address if it matches a network statement, but can only form neighbor relationships on the primary).

- if you have multiple routers sharing a segment where you are configuring secondary addressing each of the routers needs to use the same subnet as the primary address.

HTH

Rick

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