1. Performance problems on Ethernet networks
when the e0m management interface is on the
same subnet as production traffic
KB ID: 2013683 Version: 2.0 Published date: 11/29/2011
Symptoms
Network performance over ethernet networks after reboot/maintenance has degraded.
Slow backup and transfer issues are reported on a storage system when performing the following
backup and transfers:
NDMP backup
SnapMirror transfer
SnapVault transfer
Cause
Having the network management interface, which is currently a 100 megabit connection,
configured with an address that is on the same network as a gigabit, or even 10 gigabit network
interfaces, can cause the gateway for that network to get associated with the management
interface. This can have a large impact on the performance of the network traffic.
This impact is more noticeable when the e0M interface is configured with an IP address in the
same subnet as the default gateway for that system.
NetApp storage systems use a feature called Fastpath to decrease the overhead needed to lookup
routes in the routing table by using interface-to-mac caching. If the e0M interface is in the same
subnet as production traffic, it is possible that when traffic is received on a 1Gbps or 10Gbps
interface, replies can be sent from the 100Mbps e0M interface.
Similarly, when the e0M interface is in the same subnet as the default gateway, it is very likely
that the default route will be associated with the e0M interface, causing outbound routed traffic
(even if a reply to incoming traffic from a remote subnet) to use the 100Mbps e0M interface.
Solution
Perform the following steps to resolve the issue:

2. 1. Take down the management interface and allow the default gateway or static routes to get
mapped to another interface.
2. Assign an IP address to the e0M management interface from a different subnet, one
dedicated for management traffic and isolated from production traffic.
If the environment is such that the e0M interface cannot be re-assigned to a dedicated
management subnet, then e0M should be unplugged and left unconfigured. In this case,
management traffic should be allowed to run over the production network interfaces.