xor in etherchannel

[prashantrecon]

when we transfer  the data from site 1 to site 2

site1--172.x.x.98

site2--172.x.x.100

As two links are there in etherchannel and both sides are src-dst ip based loadbalance.

So when i transfer the data from site 1 it will choose link 0 right ? from site1

If i transfer the data from site 2 to site 1 ie from 172.x.x.100 to 172.x.x.98

Than which link will be selected? from site2

[Lee Smitherman]

Hi,  As far as I understand it,  if you are using TWO links in the channel and source-dest IP loadbalance then you use the last bit of the last octect to XOR

So 100 = 01100100   using the last bit of 0

       98 = 01100010 using the last bit of 0

XOR 0 and 0 = 0 so link 0.

So that would also be true of Site2 to site 1.

I did read an article (I cannot find) which in this scenareo would use other metrics to stop only one link being used.

[prashantrecon]

nput		Output
A	B
0	0	0
0	1	1
1	0	1
1	1	0
Select An Input Value	None          0 XOR 0          0 XOR 1          1 XOR 0          1 XOR 1

Is it is table right ?

[Lee Smitherman]

It is, my appologies,  been a while since using XOR.  Corrected above.

[prashantrecon]

So it will use Link 0

[Lee Smitherman]

Yup. I found the article,  well actually its a book, If you can get hold of or borrow the CCNP Switch book (Cisco CCNP Switch 642-813) it has a fantastic overview of the above.

[Alessio Andreoli]

Correct table.

eXclusive OR (XOR) is "true" only when :

a)only one input is 1

b) at least one input is 1

both these conditions must be verified for the XOR result to be 1.

Alessio