Implementing Spanning Tree

1. Implementing Spanning Tree Module 3 - Part 4Etherchannel Jane Brooke (Centennial College)mods by Emerson Hunt

2. EtherChannel

3. About EtherChannel • Logical aggregation of bandwidth • Viewed as one logical port • by STP, trunking, access and for administration • Bind 2 - 8 ports • Yields 1600Mbps (FastEther) or 16Gbps(GigabitEther) • Load balancing algorithm differs by platform

4. Etherchannel Benefits • Use all available bandwidth by logically “bundling” up to eight physical links • The logical Etherchannel can be managed as a single unit called a port channel or channel group • Seen as one by • Shutdown/no shutdown • Sh spanning tree • Sh interface trunking

5. Etherchannel Benefits • Load is balanced across physical links • Although balancing algorithm is not necessarily optimal • Under some circumstances balancing is uneven • Remaining links continue to operate if a member of the etherchannel bundle fails • Loss of a line in an etherchannel is not seen by STA • Failover time is only milliseconds

6. Used Where? • L2 as trunk between two switches • L3 as connection between two routers • Access link • typically between switch and server with appropriate NICs (NIC "teaming")

7. Etherchannel and Servers • Multiple NICs can be installed in a server and a higher bandwidth aggregated link can be formed between the server and the switch • Known as ``nic teaming`` • May not be supported natively by the server OS • Proper choice of the load balancing algorithm is important with NIC teaming

8. EtherChannel Dynamic Trunk Negotiation Protocols PAgP • Cisco proprietary • Sends PAgP packets across link to negotiate EtherChannel LACP • IEEE standard 802.3ad • Sends LACP packets across link to bundle multiple ports into a single channel • Use in mixed switch environment

9. EtherChannel Interface Modes • ON– Forces EtherChannel ON without PAgP or LACP negotiation (not recommended) • PAgP • Auto (default PAgP mode) • interface enters passive negotiating state • responds to PAgP packets received but doesn’t initiate PAgP negotiation • Desirable (PAgP mode) • interface actively negotiates with other interfaces • PAgP packets are exchanged • LACP • Passive (Default LACP mode) • port responds to LACP packets received, but it does not initiate LACP packet negotiation • Active • port actively negotiates state with other ports by sending LACP packets

10. The Defaults • Auto for PAgP and passive for LACP • Means that by default, links WILL NOT aggregate automatically • Best practice is to • Explicitly set aggregation protocol using the channel-protocol command • manually configure using the channel-group command • PAgP is the proprietary default link aggregation protocol on Cisco switches • Use LACP for vendor neutrality

11. PAgP • PAgP packets sent between Etherchannel ports – negotiate forming channel • Etherchannel seen as single bridge port to spanning tree • Packets sent every 30 seconds • Multicast out MAC 01-00-0C-CC-CC-CC • Ensures all ports have same speed, duplex and VLAN info

12. The Rules • All links in a channel-group must be almost identical • Speed and duplex • Switch port mode (trunk or access) • If access, belong to same vlan • If trunk, same vlans allowed • Each etherchannel must be assigned a channel group number (1-64) • Creates a Port-channel interface section in running config

13. Guidelines for Configuring EtherChannel

14. Guidelines for Configuring EtherChannel (Cont.) Interfaces in the same bundle can support varying port costs

15. About EtherChannel Configuration Commands • Configure PAgP interface range blah blah channel-protocol pagp channel-group X mode auto • Configure LACP interface range blah blah channel-protocol lacp channel-group X mode active • Verify show interfaces fastethernet 0/1 etherchannel show etherchannel 1 port-channel show etherchannel 1 summary

16. Configuring L2 EtherChannel • Specify the interfaces to configure in the bundle Switch(config)#interface range interface slot/port - port • Specify the channel protocol either pagp OR lacp Switch(config-if-range)#channel-protocol {pagp | lacp} PAgP is default on Cisco switches. • Create the port-channel interface and place the interfaces as members Switch(config-if-range)#channel-group number mode {auto | desirable | active | passive | on}

17. Verifying EtherChannel Switch#show running-config interface port-channel num • Displays port-channel information Switch#show run interface port-channel 1 Building configuration... Current configuration : 66 bytes ! interface Port-channel1 switchport mode dynamic desirable end Switch#show running-config interface interface x/y Switch#show run interface gig 0/9Building configuration... Current configuration : 127 bytes ! interface GigabitEthernet 0/9 switchport mode dynamic desirable channel-group 2 mode desirable channel-protocol pagp end • Displays interface information

18. Verifying EtherChannel (Cont.) Switch#show interfaces gigabitethernet 0/9 etherchannel Port state = Up Mstr In-Bndl Channel group = 1 Mode = Desirable-Sl Gcchange = 0 Port-channel = Po2 GC = 0x00020001 Pseudo port-channel = Po1 Port index = 0 Load = 0x00 Flags: S - Device is sending Slow hello. C - Device is in Consistent state. A - Device is in Auto mode. P - Device learns on physical port. d - PAgP is down. Timers: H - Hello timer is running. Q - Quit timer is running. S - Switching timer is running. I - Interface timer is running. Local information: Hello Partner PAgP Learning Group Port Flags State Timers Interval Count Priority Method Ifindex Gi0/9 SC U6/S7 H 30s 1 128 Any 15 Partner's information: Partner Partner Partner Partner Group Port Name Device ID Port Age Flags Cap. Gi0/9 DSW122 0005.313e.4780 Gi0/9 18s SC 20001 Age of the port in the current state: 00d:20h:00m:49s

19. Load Balancing • Etherchannel provides a choice of algorithms to determine which bundle member will carry a given frame • Various load-balancing methods are available (choices are platform dependant) • The default method may lead to some members being more heavily utilized than others

20. Example • Suppose we have an Etherchannel connecting a switch to a server • One type of algorithm depends solely on destination mac address • All frames destined for the same mac address will use the same wire • Therefore virtually all server bound frames will use just one wire in the etherchannel

21. Balancing Methods • src-ip • dst-ip • src-dst-ip • src-mac • dest-mac • src-dst-mac • src-port • dst-port • src-dst-port Available Methods & which is the defaultvary by platform

22. Configuring EtherChannel Load Balancing Switch(config)#port-channel load-balance type • Note that this is a global command • I.e. method cannot be configured on a per-channel basis • To see the current load balancing method, use the following: Switch#show etherchannel load-balanceSource XOR Destination IP address

23. Notes • the default method will usually result in a fair balancing • the following command will give some sense of the fairness of the load balancing algorithm • show etherchannel port-channel XLook for the "load" value on each channelThey should be similar

24. Resources • http://networkers-online.com/blog/2008/07/etherchannel-load-balancing-case-study/

25. Personal Notes • Etherchannel works (sort of) in Packet Tracer • I have had PT 5.1 crash when playing with multiple Etherchannels • Packet tracer definitely does not accurately simulate show command output where port channels are involved • However, etherchannel also seems a bit flakey on our equipment • Lab suggests "flapping" the interfaces if the Etherchannel does not come up