Port Channel Commands 625
A LAG failure of one or more of the links does not stop traffic in any manner.
Upon failure, the flows mapped to a link are dynamically reassigned to the
remaining links of the LAG. Similarly when links are added to a LAG, the
conversations may need to be shifted to a new link.
The purpose of link aggregation is to increase bandwidth between two
switches. It is achieved by aggregating multiple ports in one logical group. A
common problem of port channels is the possibility of changing packets order
in a particular TCP session. The resolution of this problem is correct selection
of physical port within port channel for transmitting the packet to keep
original packets order.
The hashing algorithm is configurable for each LAG. The types of LAG
algorithms available may vary depending upon platform capabilities.
Typically, an administrator is able to choose from hash algorithms utilizing
the following attributes of a packet to determine the outgoing port:
• Source MAC, VLAN, EtherType, and incoming port associated with the
packet.
• Source IP and Source TCP/UDP fields of the packet.
• Destination MAC, VLAN, EtherType, and incoming port associated with
the packet.
• Source MAC, Destination MAC, VLAN, EtherType, and incoming port
associated with the packet.
• Destination IP and Destination TCP/UDP Port fields of the packet.
• Source/Destination MAC, VLAN, EtherType, and incoming port
associated with the packet.
• Source/Destination IP and source/destination TCP/UDP Port fields of the
packet.
LAG Hashing
The purpose of link aggregation is to increase bandwidth between two
switches. It is achieved by aggregating multiple ports in one logical group. A
common problem of port channels is the possibility of changing packets order
in a particular TCP session. The resolution of this problem is correct selection
of a physical port within the port channel for transmitting the packet to keep
original packets order.
2CSPC4.XCT-SWUM2XX1.book Page 625 Monday, October 3, 2011 11:05 AM