Operating instructions
Chapter 5. Cisco Systems IGESM management and user orientation 71
In scenario 5, we attempt to utilize the uplink ports on the IGESM to manage the IGESM, and
use the uplink port of the Management Module to manage the Management Module, but we
place them in the same VLAN and presumably the same IP subnet.
In this design, at times both the Management Module and the IGESM vie for control of the IP
address on the IGESM (by way of each sending out gratuitous ARPs for the IGESM’s IP
address toward the upstream network), and upstream devices can become confused about
the best path to the IGESM. This design may work at times and at other times fail, as
upstream devices may try to send packets destined for the IGESM directly to the IGESM over
its uplinks (works) or to the Management Module (during the gratuitous ARP war), at which
point the Management Module may or may not pass this data on to the IGESM (fails).
Figure 5-49 demonstrates these issues.
Because of the unexpected and uncontrolled outcome of this design, it is not recommended.
Figure 5-49 Upstream issues: Why scenario 5 is not recommended
Management
Module
BladeCenter
MGMT interface
VLAN X
IP – 172.16.1.10
ETH 0
ETH 1
Sw Bay - external
management
over all ports
enabled
I own 172.16.1.10
My MAC is IGESM MAC
I own 172.16.1.10
My MAC is MM MAC
External device ARP –
Who owns IP 172.16.1.10?
External management over all ports: enabled
MM and IGESM management in same VLAN and IP subnet on upstream network
Both MM and IGESM respond to inbound ARP requests for IGESM IP.
Issue A:
If upstream device gets MM MAC, any packets sent to it for the IGESM IP address will usually not
be responded to (failed connection). If upstream device gets MAC of IGESM, packets will be sent
directly to IGESM and IGESM will respond (successful connection).
Issue B:
To compound further, when the IGESM sees the MM’s ARP response, it sends out a gratuitous
ARP saying that it owns the IP address. The MM then sends its own ARP response saying it owns
it and… ARP war, as ARPs are sent back and forth for contention over ownership of the address.
End result: Intermittent Telnets and pings to the IGESM with this configuration
VLAN X
1
2 2