EtherChannel

 Please be advised that this article is work-in-progress. The information here may be vague, incomplete, misleading or plainly wrong.  -> EtherChannel -> definition -> link aggregation technology -> multiple parallel links between two devices are treated as one logical link -> can operate at L2 or L3							 -> provides -> redundancy -> if one of the bundled ports fails, the others continue to operate -> loop prevention -> as the bundled ports are treated as one entity, the STP won't block them -> increased bandwidth -> the traffic sent on the EtherChannel port is balanced between all the ports that make up the EtherChannel -> function -> multiple physical interfaces bundled together are called a PortChannel -> the configuration applied on the portchannel is applied on all the interfaces that make it							-> if multiple EtherChannels exist between two devices, STP will block an entire EtherChannel -> all the interfaces that make it up							-> if multiple links of an EtherChannel fails, the EtherChannel functions as long as at least one physical link is still up							-> the configuration commands applied on a PortChannel are applied to all the interfaces bundled in the portchannel -> EtherChannels can be -> manual -> the interfaces are always part of the EtherChannel -> mode ON															 -> uses no negotiation protocol -> interfaces are placed in the EtherChannel regardless of their settings -> disadvantages -> link status can't be communicated to the other side -> if there is a condition that causes packet loss, but the link is up, the data still flows over the affected link -> dynamic -> uses protocols to negotiate if a physical link becomes part of an Etherchannel or not -> PAgP -> Port Aggregation Protocol -> Cisco proprietary -> modes -> AUTO -> the interface responds to PAgP packets but does not initiate negotiations -> DESIRABLE -> the interface initiates negotiations with the neighbouring interface by sending PAgP packets -> SILENT -> not a mode as auto and desirable are. -> allows establishing EtherChannels with Non PagP switches -> basically what it does is to add ports to the EtherChannel without requiring receival of PAgP packets -> this behaviour can be deactivated with non-silent keyword which will the require the receival of PAgP before adding interface to EtherChannel -> PDU -> Ethernet -> Destination address: 0100:0CCC:CCCC -> ethertype: 0x0104 -> LACP -> IEEE standart -> 802.3ad -> LACP version 1 -> 802.1ax -> LACP version 2 -> faster convergence (LAC Fast) -> bidirectional LACP communication -*> be advised that what follows is based on Cisco's implementation of the protocol -> modes -> ACTIVE -> initiates EtherChannel communication with the remote end interface -> sends LACP packets -> if the interface receives an LACP packet from the other end, an LACP adjacency is formed. -> this mode will result in an active LACP link regardless of the LACP mode configured on the remote end interface. -> PASSIVE -> the interface does not initiate an EtherChannel communication -> does not send LACP packets -> if an LACP packet is received fro the remote end -> the interface will respond -> will try to establish an LACP adjacency -> if both interfaces on the ends of the link are set to PASSIVE, neither of them will initiate LACP communication, thus, an LACP adjacency will NOT form. -> the above is confirmed -> when LACP is set to passive using 'channel-group 1 mode passive' -> a ton of CDP messages will be sent -> no LACPDUs -> LACP Fast -> with LACP regular operation, PDUs are sent every 30 seconds and it takes 3 intervals with no packets to deem the link unusable (90 seconds) -> with LACP Fast,packets are sent every 1 second which means that a faulty link can be identified in 3 seconds. -> LACP Min-Links -> the minimum required number of active links for the EtherChannel to go up -> LACP Max-Links -> the maximum number of interfaces that can be active in the EtherChannel. -> interfaces in the port-group above that number will be placed in Hot-Standby mode -> at a minimum has to be configured on the Master switch (it is responsible to select the active interfaces), and the partners switch will follow. Recommended to be configured on both -> LACP Priority -> system priority -> to form an EtherChannel, both devices must select the same interfaces (and therefore links) as active in the group -> one of the switches from the end of the link is responsible with selecting the active interfaces -> called LACP Master switch -> also called ACTOR -> elected based on the System Priority value -> based on -> configure system priority -> device's MAC address -> it is the switch with a higher system priority (higher priority has the lower system ID) -> the other device, then selects the same interfaces as active -> port priority -> determines which interfaces are selected as active for an EtherChannel -> lower priority is better -> lower interface number is better -> a scenario where interfaces in a group have to be selected as active for an Etherchannel is when there are more interfaces in the group than the maximum allowed. -> LACPDU -> control PDU used by LACP -> details -> Ethernet -> Destination MAC address: 0180:C200:0002 -> ethertype: 0x8809 (LACP) -> LACP -> HEADER -> LACP Marker -> identifies the frame as a LACP frame -> value 0x01 indicates 'slow protocols subtype: LACP' -> Version number -> the version of LACP -> Actor System Priority: integer value that ranges from 0 to 65535 -> Actor system ID: The MAC adress of the device -> Actor Key -> unique identifier for the device's sending (egress) port -> Actor Port Priority: the priority of the port -> Partner system Priority -> Partner System ID																																								 		  			  					-> Partner Key -> the unique identifier for the LACPDU receiver's port -> Partner Port Priority -> TLVs -> for carrying additional information -> contains -> LACP syste priority -> LACP interface priority -> interface number -> MAC address -> operational key -> notes on configuration -> a channel-group doesn't necessarily needs the same LACP mode on all ports -> for example, in channel-group 1, port 1 can be ACTIVE and port 2 can be PASSIVE and both of them can work -> however, the remote switch must be configured so that EtherChannel communication is possible. -> this approach is not recommended. The configuration must be consistent across all ports in the same etherchannel -> purpose -> the static or dynamic settings are ALWAYS configured manually on the device. -> the interface on the other end of a LACP configured link will NOT be autoconfigured and added to the EtherChannel. What happens is that if both ends are correctly configured, the link formed by these interfaces will be added to the EtherChannel operation. Traffic will flow, and so on. The advantages of a dynamic protocol is that faults can be easily found, the prioritization of one link over the other and so on. -> a port added to a PortChannel is incompatible with the other ports (settings) or with its neighbour -> it remains part of the PortChannel -> it is not used in the EtherChannel -> steps -> an interface is added to the PortChannel -> if the settings matches with the other interfaces in the Portchannel in might be used in an EtherChannel -> if the settings doesn't match with the other interfaces in the PortChannel -> it is placed in a nonworking state -> it remains part of the PortChannel -> the link with the neighbour is not part of the EtherChannel -> the PAgP/LACP negotiation starts between the neighbouring interfaces and if they are successful, the link will be used as part of the EtherChannel -> implementation restrictions -> only same type interfaces cand be bundled in a PortChannel -> Gigabit - Gigabit -> FastEthernet - FastEthernet -> up to a maximum of 8 interfaces can be bundled in a PortChannel -> LACP supports 16 interfaces in a channel -> 8 active -> 8 standby -> PAgP supports only 8 active interfaces in a channel -> the interfaces bundled together must have the same configuration -> speed -> duplex mode -> VLAN settings -> access -> which VLAN -> trunk -> allowed VLANs -> native VLAN -> STP settings -> the interfaces on both ends on the EtherChannel must have the same settings -> the settings on the neighbours are verified using -> PAgP -> LACP -> CDP -> speed, duplex mode, VLAN settings (access, trunk) -> STP mode can be different -> troubleshooting -> verify if the settings of the PortChannels on the ends of the EtherChannel match -> verify the switch for -> CDP messages -> err-disabled messages -> cannot-bundle messages -> verify the type of the ports -> switching port -> routing port -> all ports in the bundle must be configured the same -> verify the VLAN settings on the ports -> access or trunk -> for trunk, allowed VLANs must be the same -> for a switching etherchannel, the native vlan must be consistent on all the ports -> all interfaces must have -> the same speed -> the same duplex -> the same MTU -> Load interval -> storm control -> the links must be ptp between devices. -> member ports must be all active -> the modes of the dynamic protocols configured -> all member interfaces must be consistently configured -> dynamic protocols PDU transmission and receival on both ends -> notes -> terminology -> EtherChannel -> the name of the port aggregation technology itself -> the link between two PortChannels -> PortChannel -> a virtual (logical) port consisting of multiple aggregated physical ports working as one -> Channel Group -> the "group" of ports making up the Port"Channel" -> EtherChannel Load Distribution -> the rules a switch follows when choosing which physical link from a PortChannel bundle to use when forwarding traffic -> the switch calculates a hash based on fields of the packet's header and forwards frames based on that hash -> the hash calculation may be based on the following fields. -> MAC -> source -> example -> in a given time frame, all frames with the same source MAC address will be forwarded out of the same link -> destination -> both -> IP -> source -> destination -> both -> L4 Port -> source -> destination -> both -> the purpose of ECLD is to -> cause all frames in a single application flow to be forwarded on the same link (avoid message reordering) -> integrate the ECLD algorithm into the ASICs for better performance -> to use all the active links in the bundle -> balance the traffic across active links (within the constraints of the first three goals) -> using the distribution method corresponding to the field with the most variety in values provides the best load balancing. -> the hash is a binary function so, for best load balancing, EtherChannels should have powers of two number of active links (2, 4, 8) -> Layer 3 Etherchannel -> the logic of the L3 EtherChannel technology is the same as for L2 EtherChannel -> L3 EtherChannel refers to bundling multpile routing ports together ( as opposed to multiple switchports ) -> the result is the creation of a single PortChannel group, working as a single routing interface -> the EtherChannel can be created manually or dynamically -> creation -> the MLS interfaces are put into routing mode ((conf-int-range)# no switchport) -> the PortChannel is created ((conf-int-range)# channel-group X mode YYYYYY) -> move to the PortChannel config mode ((conf-int-range)# interface port-channel X)									-> put the PortChannel into routing mode ((conf-int)# no switchport) -> set an IP address for the PortChannel ((conf-int)# ip address ...) -> troubleshooting -> the interfaces must be put into routing mode before being bundled together in a PortChannel. Otherwise an error will be thrown and the PortChannel has to be deleted and recreated. -> for the EtherChannel to be formed, the interfaces has to work at the same speed and duplex mode -> if the EtherChannel is successfully created -> the portchannels for both switches will have Conencted routes in the routing table -> the "etherchannel summary" command shows (RU) as the state of the PortChannel. -> the "show interfaces port-channel" will display an IP address -> references -> http://networkingbodges.blogspot.com/2012/12/all-sorts-of-things-about-lacp-and-lags.html