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Cisco 4500X EtherChannel Symmetric Load Balancing

Mate Grbavac
Level 1
Level 1

Hi,

I have probem with symmetric load balancig, in case when both ends of ether channel are on the sam switch (we are using VLAN translation).

We need to create L2 port channel with both ends on same switch (Cisco WS-C4500X-24X-ES), for example:

Po1 – Gi0/1, Gi0/3 (one end of port channel)
Po2 – Gi0/2, Gi0/4 (other end of port channel)

On ports in Po2 we will configure VLAN mapping.

My question is what is the best ether-channel load-balancing scheme with wich we can accomplish full symmetry in both directions? For example, if traffic in one direction goes through Gi0/1 (member of Po1), in other direction also must go through Gi0/1.

This is required because we need to connect four appliances for DPI (they are full L2 transparent) and traffic through each appliance need to be symmetric.

I can set-up src-ip, dst-ip, src-dst-ip etc. load balancing, but, actually I need src-ip on Po1 and dst-ip on Po2. Is there any way to set up different load balancing mechanism for different ether channel on same switch (4500X).

See the picture...

EtherChannel_LoadBalancing.jpg

Best regards,

Mate

4 Replies 4

acampbell
VIP Alumni
VIP Alumni

Hi,

According to the config guide for 4500X (IOS 15.1.2)

http://www.cisco.com/en/US/docs/switches/lan/catalyst4500/15.1.2/XE_340/configuration/guide/channel.html#wp1020804

Configuring EtherChannel Load Balancing


Note Load balancing can only be configured globally. As a result, all channels (manually configured, PagP, or LACP) use the same load-balancing method.


You CANNOT use different load balancing methods

Regards,
Alex.
Please rate useful posts.

Regards, Alex. Please rate useful posts.

O.K., tnx.

My other question is,

if I set up src-dst-ip load balancing, should the any combination of two IP addreess give same result?

Fore example (port channel with 4 ports),

  • Source IP: 10.10.10.1
  • Destination IP: 20.20.20.1

will use second port in port channel.

If we switch IP adresses:

  • Source IP: 20.20.20.1
  • Destination IP: 10.10.10.1

should that traffic use same port (second) in port channel like in first example?

Hello,

My answer should be "yes" because switch balancing use a XOR and XOR (A,B)= XOR(B,A).

But your topology can be dangerous and I cannot ensure you that it is ok. We use

a similar topology but with two different switches and use the same port numbers switchA-port1 to switchB-port1

and switchA-port2 to switchB-port3  to avoid asymetric traffic.  Besides, we create an alternative link (for backup purposes) that is blocked by RSTP and only is actived when there are problems.

So, the best way to check your topology is using the following commands:

test etherchannel load-balance interface Po1 ip 10.10.10.1 20.20.20.1

test etherchannel load-balance interface Po2 ip 20.20.20.1 10.10.10.1

If the results is not right, consider re-patch your connections (cross it!).

I know this commands work in c3750. Check if your catalyst are supported.

Regards.

I tried to connect 4500X with 3560G through 4 links in port channel, but there is no symmetric load balancing. I tried src-dst-ip on both sides, src-ip on one and dst-ip on other side (and vice-versa) but nothing...

Ports was connected in manner Ten1/1 <--> Gi0/1, Ten1/2 <--> Gi0/2, Ten1/3 <--> Gi0/3, Ten1/4 <--> Gi0/4)

When I connect 3560G with 2960 things are getting better. I suppose that reason for that is fact that 3560G and 2960 are using sam load balancing algorythm (I'm not sure about that, that's my opinion).

What do you think?

Is there any (cheaper) platform whic is using same etherchannel load balancing algorythm as 4500X?

Best regards