AIX Networking

IBM AIX offers robust networking features tailored for enterprise reliability and performance on Power Systems. Whether you’re managing physical NICs, virtual adapters in LPARs, or advanced setups like RDMA and link aggregation, understanding AIX networking is crucial for admins aiming to maximize throughput, security, and uptime.

This post dives into network interfaces, IP configuration, VLANs, TCP/IP tuning, monitoring, advanced features, and troubleshooting, with examples and a detailed ASCII diagram to visualize your architecture.

Network Interface Basics

AIX distinguishes between:

• Physical adapters (entX) – Real network interfaces.
• Logical interfaces (enX) – Virtual interfaces, including VLANs.

Listing Adapters:

# lsdev -Cc adapter   # List physical NICs

# lsdev -Cc if        # List logical interfaces

Each interface has attributes like:

• MTU – Default 1500 bytes; jumbo frames up to 65,536.
• Speed & Duplex
• State – Available / Defined / Failed

Detailed Stats:

# lsattr -El ent0      # Attribute settings

# entstat -d ent0      # Adapter stats: errors, drops, collisions

Virtual Ethernet adapters in PowerVM LPARs enable inter-partition communication without physical hardware.

IP Configuration

Temporary:

# ifconfig en0 192.168.1.10 netmask 255.255.255.0 up

# route add default 192.168.1.1

Persistent:

# chdev -l en0 -a netaddr=192.168.1.10 -a netmask=255.255.255.0

# chdev -l inet0 -a route=192.168.1.1

Aliases & Name Resolution:

# ifconfig en0 192.168.1.11 netmask 255.255.255.0 alias

Edit /etc/hosts for static hostnames and /etc/resolv.conf for DNS. Use SMIT for easier management:

# smitty tcpip

# smit mktcpip

VLAN and SEA Support

VLANs:

# mkdev -c if -s vlan -t ent0 -a vlan_id=10  # Creates ent0.10

ifconfig ent0.10 10.0.10.5 up              # Assign IP

SEA (Shared Ethernet Adapter) in PowerVM:

# mkvdev -sea ent0 -vlanid 20

Feature	Command Example	Use Case
Base VLAN	mkvdev -vlan ent0 -vlanid 20	Single NIC segmentation
SEA VLAN	mkvdev -sea entX -vlanid 30	LPAR traffic isolation
IP on VLAN	ifconfig ent1 10.0.20.5 up	Per-VLAN addressing

TCP/IP Stack and Routing

Protocols: TCP (reliable), UDP (fast), ICMP (ping/traceroute), IPv6.

Static Route:

# chdev -l inet0 -a route=10.0.0.0 -a netmask=255.255.0.0 -a gateway=10.0.0.1

Dynamic Routing: Enable via:

# no -o ipforwarding=1

Performance Tuning

Buffers:

# no -o tcp_sendspace=1048576 -o tcp_recvspace=1048576

MTU:

# chdev -l en0 -a mtu=9000  # Jumbo frames

Queues:

# chdev -l ent0 -a receive_size=60 -a transmit_size=60

Latency:

# no -o tcp_nodelayack=1

# no -o thewall=4096

Link Aggregation (EtherChannel):

# smitty etherchannel  # Combine up to 8 NICs for throughput/failover

Security essentials: IPSec, VLAN isolation, SSH, Kerberos, TCP wrappers (/etc/hosts.allow).