I was reading through the topic on Ether-Channels, and I'm quite confused, and need your guys guidance..
taken from a book im reading,
For example, an EtherChannel consisting of two links bundled together requires a 1-bit
index. If the index is 0, link 0 is selected; if the index is 1, link 1 is used. Either the lowestorder address bit or the XOR of the last bit of the addresses in the frame is used as the index. A four-link bundle uses a hash of the last 2 bits. Likewise, an eight-link bundle uses
a hash of the last 3 bits. The hashing operation’s outcome selects the EtherChannel’s outbound link
As an example, consider a packet being sent from IP address 192.168.1.1 to 172.31.67.46.
Because EtherChannels can be built from two to eight individual links, only the rightmost
(least-significant) 3 bits are needed as a link index. From the source and destination
addresses, these bits are 001 (1) and 110 (6), respectively. For a two-link EtherChannel,
a 1-bit XOR is performed on the rightmost address bit: 1 XOR 0 = 1, causing Link 1 in the
bundle to be used. A four-link EtherChannel produces a 2-bit XOR: 01 XOR 10 = 11,
causing Link 3 in the bundle to be used. Finally, an eight-link EtherChannel requires a
3-bit XOR: 001 XOR 110 = 111, where Link 7 in the bundle is selected.
From what I have understand... it is possible for us to build and configure EtherChannels from 2 to 8 individual links.
My question is..
1) So it is possible to build Etherchannels with 3, 5, 6 or 7 individual links?
2) if so, a two-link etherchannel , they uses a 1-bit index... and only the rightmost least significant bits are needed as link index.
- for a four-link etherchannel, they uses a 2-bit, and for an eight-link bundle uses 3bits as the index...
so in that case, how many bits do etherchannel uses for a 3-link, 5-link, 6 and 7-link bundles?
please kindly direct me in the right direction ... thanks...
Yes, you can have 3, 5 or 7 links in an Etherchannel, but the distribution is not going to get done evenly. When building Etherchannels, It is recommend to configure them with the power-of-2. So 2, 4 or 8. Etherchannel has 8 "buckets" to distribute among member ports.
So a 2 port bundle have 2 4 port buckets and a 4 port bundle has 4 2 port buckets and 8 port bundle has 8 1 port bucket, but for example an uneven bundle of 3 would have 2 3 port buckets and 1 2 port buckets.
For combinations about 2 links i.e. 3 through 8, the switch uses 3 bits. The
switch will allocate the states such that all hashes have a corresponding
link identified. This is similar to a situation where you have an 8 port
etherchannel and one of the ports went down. Please check the following
Hope this helps.