3Com WX2200 3CRWX220095A Switch User Manual

Distributed MAPs and DHCP Option 43
The option 43 field in a DHCP Offer message can provide a simple and
effective way for MAPs to find WX switches across an intermediate Layer
3 network, and is especially useful in networks that are geographically
distributed or have a flat domain name space. You can use the DHCP
option 43 field to provide a list of WX IP addresses, without the need to
configure DNS servers.
To use DHCP option 43, configure the option to contain a
comma-separated list of WX IP addresses or fully qualified hostnames
(host name and domain name; for example, host.domain.com), in the
following format:
You can use an IP address list or a hostname list, but not both. If the list
contains both types of values, the MAP does not attempt to use the list.
The ip and host keywords can be in lowercase, uppercase (IP or HOST),
or mixed case (example: Ip, Host, and so on.) You can use spaces after
the colon or commas, but spaces are not supported within IP addresses or
hostnames. Leading zeroes are supported in IP addresses. For example, is valid.
Valid characters in hostnames are uppercase and lowercase letters,
numbers, periods ( . ), and hyphens ( - ). Other characters are not
If you use the host option, you must configure the network’s DNS server
with address records that map the hostnames in the list to the WX IP
After receiving a DHCP Offer containing a valid string for option 43, a
Distributed MAP sends a unicast Find WX message to each WX switch in
the list. See “How a Distributed MAP Contacts a WX Switch
(DHCP-Obtained Address)” on page 190 for a description of this process.
No configuration is required on the WX.