Port Channels

Port channeling allows to aggregate multiple links into one logical interface to provide higher aggregated bandwidth, load balancing and link redundancy.

Cisco MDS switch supports two types of Port Channels: Fibre Channel and Ethernet.

Ethernet Port Channels group together Gigabit Ethernet interfaces on the IPS modules. It is similar to the port channels on LAN words, except:

1. don't support PAgP and LACP protocols. The port channel must be configured statically
2. can only aggregate two physical interfaces adjacent to each other on the IPS module (1-2, -4, 5-6 or 7-8)
3. are supported on IPS-4 and IPS-8 modules. They are not supported on MPS14/2 and 9216i dual GigE ports.
4. If you are running a single FCIP tunnel on an Ethernet Port Channel, only one of the two links will be used under normal conditions, because of the load balancing on the Cat Ethernet switches. There's a 50/50 chance that IPS module will use one link for outbound traffic, and Cat Ethernet switch will use the other link for inbound traffic.

Fibre Channel port Channels group together FC or FCIP tunnel interfaces:

1. Up to 16 interfaces across different slots can be grouped together
2. MDS supports up to 128 port channels with a mix of Gen-1 and Gen-2 modules
3. MDS supports up to 256 port channels when only Gen-2 modules are installed in a switch
4. Each group of physical links appears to FSPF (Fibre Channel Routing protocol) as one logical link. 
5. Only E and TE ports can be port channeled. F ports cannot be port channeled (HBAs and Storage don't support it)
6. Port Channels between Cisco and non-Cisco switches are not supported
7. Load balancing is performed per VSAN based on the VSAN parameter: vsan 1 loadbalancing [src-dst-id | src-dst-ox-id]. By default, load balancing is Exchange based (src-dst-ox-id) and can be changed to Flow based (src-dst-id). The same VSAN load-balancing parameter applies to Port Channels and equal-cost FSPF paths.

Port Channel protocol uses EPP (exchange peer parameters) SW_ILS frames. SW_ILS fames are special Fibre Channel frames exchanged between storage switches on ISL links. There are mane kinds of SW_ILS frames and EPP is one of them.

Port Channel protocol consists of two sub-protocols:

1. Bring-up Protocol. When Port Channel comes up, two peering switches exchange Port Channel configuration. If the settings don't match, the Port Channel  individual interfaces go into an isolated mode (port channel up, but doesn't pass any data). As soon as settings match on both ends, the Port Channel will become operational. The following settings should match at both ends of the Port Channel:
1. Port Type (FC or FCIP)
2. Configured Port mode (AUTO or E)
3. Trunk mode (ON, OFF or AUTO)
4. Port Speed 
1. Generation-1: Auto, 1000 or 2000
2. Generation-2: Auto, Auto MAX 2000, 1000, 2000 or 4000
3. Generation-3: Auto, Auto MAX 2000, AUTO MAX 4000, 1000, 2000, 4000 or 8000
5. Port VSAN
6. Trunk allowed VSAN list. Make sure that VSANs are first created on both switches before trying to use switchport trunk allowed vsan command. If a VSAN does not exist, the Port Channel will be in the isolated mode.
7. Port Security
8. FibreChannel receive buffer size 
9. This list can be viewed by running show port-channel compatibility-parameters command
2. Autocreating protocol. This protocol makes sure that ports are eligible to the part of the same port channel and that they have an eligible partner switch. It then automatically aggregates these ports into a Port Channel. 
1. This feature must be enabled manually for each individual interface
2. SAN-OS will start with number 128 for the auto-created port channels, and go down 127,126, etc. (if all modules are Gen-2, it will start with 256)
3. an autocreated Port Channel number may be different across reboots
4. If some interface doesn't join the port channel automatically, that is because its settings don't match the other ports in the autocreated port channel. That interface will come up as a separate link.
5. Any configuration changes made to the autocreated port channel are not saved under the autocreated port channel interface. Instead they are only saved under the individual interfaces that are part of the port channel. Some configuration settings cannot be made for the autcreated port channels.
6. You can convert autcreated port channel into a normal port channel
7. both sides of an autocreated port channel must be autocreated.

MDS Fibre Channel port Channels have two modes:

1. Port Channel ON mode. 
1. (conf-int)#no channel mode active
2. port channel protocol is OFF
3. you have to explicitly no shut interfaces after making them part of a port channel
4. mode is default
5. suspends interfaces if their operational values are incompatible with Port Channel
2. Port Channel ACTIVE mode
1. (conf-int)#channel mode active
2. Port Channel protocol is ON
3. port channel automatically bundles additional available interfaces
4. dynamic link recovery when adding or deleting links
5. isolates interfaces if their operational values are incompatible with Port Channel

It is not required to have the same mode on both ends of the port channel. One side can be ON (default) and the other side can be ACTIVE.

There are tree ways to create port channels:

1. configure each individual port or range of ports with channel-group X or channel-group X force command
1. Port channel X interface will be automatically created
2. port channel mode will be set to ON 
3. individual port members will be shut down and you'll have to no shut them manually
2. configure port channel interface first with interface port-channel x command. 
1. Port channel mode will be set to ON, but you can change it to ACTIVE mode by using channel mode active.
2. configure each individual port or range of ports with channel-group x or channel-group x force command.
3. Configure each individual port or range of ports with command channel-group auto and no shut them.
1. SAN-OS will use number 128 (256 for all Gen-2 modules) for the first autocreated port channel
2. you won't see port channel 128 in the configuration, but you can still conf t, int po128 and configure some of its settings. These settings will be saved to the individual port channel member interface configuration.

The force keyword on the channel-group command plays a role only when adding ports to the port channel after the port channel was already created.

We can't modifu FSPF parameters on the auto creatd port-channels. We must first convert it to a user-configured port channel:
#port-channel 128 persistent