Operating instructions

Appendix A. Hints and tips 229
solution for your environment, which will have its own unique requirements. It is only used in
these examples for simplicity.
Microsoft has published Knowledge Base article 157025 that discusses the different
approaches for default gateways on multihomed systems. This article can be found at:
http://support.microsoft.com/default.aspx?scid=kb;en-us;157025
We recommend that the BladeCenter system administrator review this document if there are
questions about how best to address this issue in your specific environment.
Duplicate IP address: part 1
Several configuration choices can result in the BladeCenter reporting duplicate IP addresses,
even when there are no known conflicts.
The most common cause of a blade server reporting a duplicate address is the result of
placing one of the interfaces of a blade server in the same VLAN as the management VLAN
of the Cisco Systems IGESMs (default is VLAN 1) with an IP address in the same subnet as
the Management address used internally by the Management Modules to communicate with
the Cisco Systems IGESMs.
In this case, the Management Module tries to act as a proxy for all addresses on this subnet
(as part of allowing external access to the Cisco Systems IGESMs through its external
interface) and answers to any query for any address on the entire internal Management
subnet. In this case, when the blade server checks to see whether its address is available in
the network (sends out an ARP request for its own address), the Management Module
responds to this ARP request for the blade server address, and the blade server assumes
that the address is in use and reports this through a Windows 2000 pop-up message.
The simplest solution is to always keep blade servers off of the Cisco Systems IGESM
management VLAN (default management VLAN for the Cisco Systems IGESMs is VLAN 1).
To reduce the likelihood of blade servers being placed on this VLAN, the Cisco Systems
IGESM sets the defaults to all ports going to the blade servers (g0/1 - g0/14) to:
switchport access vlan 2
switchport trunk native vlan 2
switchport trunk allowed vlan 2-4094
However, this does not prevent the user from adding VLAN 1 (or whatever the management
VLAN is) to ports going to the blade servers, resulting in the consequences we described.
See 5.3.12, “Scenario 6 (not recommended)” on page 72 for a more detailed explanation of
the cause of this issue.
Duplicate IP address: part 2
As noted in “Duplicate IP address: part 1,” several configuration choices can result in the
BladeCenter reporting duplicate IP addresses, even when there are no known conflicts. This
section discusses an issue with the Cisco Systems IGESM reporting a duplicate IP address.
Important: Due to this possible interaction between the blade servers and the
Management Modules, we highly recommend that you not place blade servers on the
same VLAN that is used for the management VLAN on the Cisco Systems IGESMs.