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New Member

Why does a dynamic interface need an IP address?

I've been working with wireless for awhile now and I always wondered why a dynamic interface on a wireless controller requires an IP address. If the interface is tagged with the vlan id, trunked via the phyiscal port and the interface is tied to the ssid then where does layer 3 come into play here?

Timothy Chin

CCIE #23866 (R&S)

5 REPLIES
VIP Purple

Why does a dynamic interface need an IP address?

HI,

A dynamic interface is simply an interface that maps a WLAN to a wired vlan or subnet.Dynamic interfaces, also known as VLAN interfaces, are created by users and designed to be analogous to VLANs for Wireless LAN clients. Dynamic interfaces to be used to control and secure the traffic on the WLAN just like we would use vlans and subnets on the lan for that purpose. Each dynamic interface controls VLAN and other communications between controllers and all other network devices, and each acts as a DHCP relay for wireless clients associated to WLANs mapped to the interface.

I hope you understand my point.

http://www.cisco.com/en/US/docs/wireless/controller/7.4/configuration/guides/consolidated/b_cg74_CONSOLIDATED_chapter_0110110.html

REgards

New Member

Why does a dynamic interface need an IP address?

I understand this but in your answer you also mention the interface acting as a DHCP relay. I think I now understand why a dynamic interface requires an IP address. This would have to do with the interface acting as a DHCP relay where the interface would send the IP address information to the DHCP server for subnet determination correct?

Timothy Chin

CCIE #23866 (R&S)

VIP Purple

Re: Why does a dynamic interface need an IP address?

Hi,

Yes,

Dynamic interfaces are also known as VLAN interfaces. They are user defined interfaces and are used to carry the data from wireless clients. They are created with the following details: VLAN ID, Physical port assignment, DHCP server information, ACL information.

This is the reason: Dynamic Interfaces must be configured on a unique (to the WLC) IP network and VLAN.

For more about DHCP ON WLC:

http://www.cisco.com/en/US/products/ps6366/products_tech_note09186a0080af5d13.shtml

Regards

Dont forget to rate helpful posts

VIP Purple

Re: Why does a dynamic interface need an IP address?

In simplest terms, even though WLC does not do inter-vlan routing, it should keep the clients' IP  address in its database. So when wireless client request an IP controller will proxy (default behaviour) dhcp request & use its own dynamic interface IP to communicate with wired network. Assume WLC does not have IP address in subnet allocated for each WLAN, then users having problem of getting IP.

This is also important for roaming as well. In these scenario WLCs will talk to each other & inquire about a roamed client IP to see any other controller support those client's subnet. So it is important WLC to know about client's IP subnet information in these scenario

HTH

Rasika

**** Pls rate all useful responses ****

Cisco Employee

Why does a dynamic interface need an IP address?

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